Pioneer Plate
Space Coin

Uncirculated Silver & Gold-Plated Pioneer Space Probe Coin

One side has an image of Pioneer orbiting Jupiter

The other side has the famous Pioneer plate with information on the Earth location and what we look like incase the probe encounters Aliens
 
The coin is 40mm in diameter and weights about an ounce
Comes in air-tight acrylic coin holder

In Excellent Condition

Would make an Excellent Gift or Collectable Keepsake
 
 

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Pioneer program Article Talk Read Edit View history Tools From Wikipedia, the free encyclopedia Not to be confused with Pioneers Program. A family portrait showing (from left to right) Pioneers 6-9, 10 and 11 and the Pioneer Venus Orbiter and Multiprobe series Program overview Country United States Organization Air Force Ballistic Missile Division United States Army NASA Purpose Lunar and interplanetary exploration Status Completed Program history Duration 1958–1960 1965–1992 First flight Pioneer 0 August 17, 1958 Last flight Pioneer Venus August 1978 Successes 9 Failures 10 Partial failures 1 Launch site(s) Cape Canaveral Air Force Station Vehicle information Launch vehicle(s) Thor-Able Atlas-Able Juno II Delta E Atlas-Centaur The Pioneer programs were two series of United States lunar and planetary space probes exploration. The first program, which ran from 1958 to 1960, unsuccessfully attempted to send spacecraft to orbit the Moon, successfully sent one spacecraft to fly by the Moon, and successfully sent one spacecraft to investigate interplanetary space between the orbits of Earth and Venus. The second program, which ran from 1965 to 1992, sent four spacecraft to measure interplanetary space weather, two to explore Jupiter and Saturn, and two to explore Venus. The two outer planet probes, Pioneer 10 and Pioneer 11, became the first two of five artificial objects to achieve the escape velocity that will allow them to leave the Solar System, and carried a golden plaque each depicting a man and a woman and information about the origin and the creators of the probes, in case any extraterrestrials find them someday. Naming Credit for naming the first probe has been attributed to Stephen A. Saliga, who had been assigned to the Air Force Orientation Group, Wright-Patterson AFB, as chief designer of Air Force exhibits. While he was at a briefing, the spacecraft was described to him, as, a "lunar-orbiting vehicle, with an infrared scanning device." Saliga thought the title too long, and lacked theme for an exhibit design. He suggested, "Pioneer", as the name of the probe, since "the Army had already launched and orbited the Explorer satellite, and their Public Information Office was identifying the Army, as, 'Pioneers in Space,'" and, by adopting the name, the Air Force would "make a 'quantum jump' as to who, really, [were] the 'Pioneers' in space.'"[1] Early missions The earliest missions were attempts to achieve Earth's escape velocity, simply to show it was feasible and to study the Moon. This included the first launch by NASA which was formed from the old NACA. These missions were carried out by the Air Force Ballistic Missile Division, Army, and NASA.[2] Able space probes (1958–1960) Reconstructed replica of Pioneer 1 Lunar flyby spacecraft (Pioneer 3, 4) Pioneer P-1, P-3, 5, P-30, and P-31 probe Mission Name Alternate Names Type Outcome Date Pioneer 0 Thor-Able 1, Pioneer Lunar orbiter Destroyed (Thor failure 77 seconds after launch) August 17, 1958 Pioneer 1 Thor-Able 2, Pioneer I Lunar orbiter, missed Moon Third stage partial failure October 11, 1958 Pioneer 2 Thor-Able 3, Pioneer II Lunar orbiter, reentry Third stage failure November 8, 1958 Pioneer P-1 Atlas-Able 4A, Pioneer W Launch vehicle lost September 24, 1959 Pioneer P-3 Atlas-Able 4, Atlas-Able 4B, Pioneer X Mission failed shortly after launch November 26, 1959 Pioneer 5 Pioneer P-2, Thor-Able 4, Pioneer V March 11, 1960 Pioneer P-30 Atlas-Able 5A, Pioneer Y Lunar probe Failed to achieve lunar orbit September 25, 1960 Pioneer P-31 Atlas-Able 5B, Pioneer Z Lunar probe Lost in upper stage failure December 15, 1960 Juno II lunar probes (1958–1959) Pioneer 3 – Lunar flyby, missed Moon due to launcher failure December 6, 1958 Pioneer 4 – Lunar flyby, achieved Earth escape velocity, launched March 3, 1959 Later missions (1965–1978) Pioneer 10 / 11 Five years after the early Able space probe missions ended, NASA Ames Research Center used the Pioneer name for a new series of missions, initially aimed at the inner Solar System, before the flyby missions to Jupiter and Saturn. While successful, the missions returned much poorer images than the Voyager program probes would five years later. In 1978, the end of the program saw a return to the inner Solar System, with the Pioneer Venus Orbiter and Multiprobe, this time using orbital insertion rather than flyby missions. The new missions were numbered beginning with Pioneer 6 (alternate names in parentheses). Interplanetary weather The spacecraft in Pioneer missions 6, 7, 8, and 9 comprised a new interplanetary space weather network: Pioneer 6 (Pioneer A) – launched December 1965 Pioneer 7 (Pioneer B) – launched August 1966 Pioneer 8 (Pioneer C) – launched December 1967 Pioneer 9 (Pioneer D) – launched November 1968 (inactive since 1983) Pioneer E – lost in launcher failure August 1969 Pioneer 6 and Pioneer 9 are in solar orbits with 0.8 AU distance to the Sun. Their orbital periods are therefore slightly shorter than Earth's. Pioneer 7 and Pioneer 8 are in solar orbits with 1.1 AU distance to the Sun. Their orbital periods are therefore slightly longer than Earth's. Since the probes' orbital periods differ from that of the Earth, from time to time, they face a side of the Sun that cannot be seen from Earth. The probes can sense parts of the Sun several days before the Sun's rotation reveals it to ground-based Earth orbiting observatories. Outer Solar System missions Map showing location and trajectories of the Pioneer 10 (blue), Pioneer 11 (green), Voyager 1 (purple) and Voyager 2 (red) spacecraft, as of April 4, 2007 The Pioneer plaque attached to Pioneers 10 and 11 Pioneer 10 (Pioneer F) – Jupiter, interstellar medium, launched March 1972 Pioneer 11 (Pioneer G) – Jupiter, Saturn, interstellar medium, launched April 1973 Pioneer H – proposed out-of-ecliptic mission for 1974, never launched. Would have used flight spare for Pioneers 10 and 11.[3] Venus project Main article: Pioneer Venus project Pioneer Venus Orbiter (Pioneer Venus 1, Pioneer 12) – launched May 1978 Pioneer Venus Multiprobe (Pioneer Venus 2, Pioneer 13) – launched August 1978 Pioneer Venus Probe Bus – transport vehicle and upper atmosphere probe Pioneer Venus Large Probe – 300 kg parachuted probe Pioneer Venus North Probe – 75 kg impactor probe Pioneer Venus Night Probe – 75 kg impactor probe Pioneer Venus Day Probe – 75 kg impactor probe See also Mariner program Pioneer anomaly Ranger program Surveyor program Timeline of Solar System exploration Voyager program References "Origins of NASA Names". NASA History. www.history.nasa.gov. Retrieved 2006-10-16. "Los Angeles Air Force Base > Home" (PDF). "Pioneer H, Jupiter Swingby Out-of-the-Ecliptic Mission Study" (PDF). 20 August 1971. Archived from the original (PDF) on 14 May 2010. Retrieved 7 July 2017. External links Wikimedia Commons has media related to Pioneer program. Pioneer (Moon) Program Page by NASA's Solar System Exploration Mark Wolverton's The Depths of Space online Thor Able – Encyclopedia Astronautica Space Technology Laboratories Documents Archive WebGL-based 3D artist's view of Pioneer @ SPACECRAFTS 3D vte Pioneer program Early missions Pioneer 0Pioneer 1Pioneer 2Pioneer 3Pioneer 4Pioneer P-1 (W)Pioneer P-3 (X)Pioneer P-30 (Y)Pioneer P-31 (Z)Pioneer 5 (P-2) Pioneer 11 at Saturn Later missions Pioneer 6Pioneer 7Pioneer 8Pioneer 9Pioneer EPioneer 10Pioneer 11 Venus missions Pioneer Venus project Pioneer Venus OrbiterPioneer Venus Multiprobe Related Pioneer plaque Eric BurgessCarl SaganFrank DrakeLinda Salzman SaganPioneer anomalyPioneer H vte Spacecraft missions to the Moon Exploration programs American ApolloArtemis-CLPSLunar OrbiterLunar PrecursorPioneerRangerSurveyorChinese Chang'eIndian ChandrayaanJapanese Japanese Lunar Exploration ProgramSouth Korean DanuriRussian Luna-GlobSoviet CrewedLunaLunokhodZond Active missions Orbiters ARTEMISCAPSTONEChandrayaan-2 OrbiterChang'e 5-T1 (service module)DanuriLunar Reconnaissance OrbiterQueqiao relay satellite (relay satellite at L2)Queqiao-2 relay satelliteTiandu-1Tiandu-2 Landers Chang'e 3Chang'e 4SLIM Rovers Yutu-2 Flybys ArgoMoon Past missions Crewed landings Apollo 111214151617(List of Apollo astronauts) Orbiters Apollo 810 Apollo Lunar ModuleArtemis 1Chang'e 125Chandrayaan-1ClementineExplorer 3549GRAILHitenLADEELongjiang-2Luna 101112141922Lunar Orbiter 12345Lunar ProspectorPFS-1PFS-2SMART-1SELENE (Kaguya, Okina, Ouna)Chandrayaan-3 (propulsion module) Impactors LCROSSLuna 2Moon Impact ProbeRanger 46789 Landers Apollo Lunar Module ×6Chang'e 5Luna 913161720212324Surveyor 13567Vikram (Chandrayaan-3)EagleCamIM-1 Rovers Lunar Roving Vehicle Apollo 151617Lunokhod 12YutuPragyan (Chandrayaan-2)(Chandrayaan-3)LEV-1LEV-2 Sample return Apollo 111214151617Luna 162024Chang'e 5 Failed landings BeresheetEmirates Lunar MissionHakuto-R M1Luna 578151825OMOTENASHISurveyor 24Vikram (Chandrayaan-2)Peregrine Mission One Flybys 4MApollo 13Chang'e 5-T1GeotailGalileoICELongjiang-1Luna 1346LunaH-MapLunar FlashlightLunar IceCubeLunIRMariner 10NEA ScoutNozomiPioneer 4Ranger 5STEREOTESSWMAPWindZond 35678PAS-22 Planned missions Artemis Artemis 2 (2025)Lunar GatewayArtemis 3 (2026)Artemis 4 (2028)Artemis 5 (2029)Artemis 6 (2030)Artemis 7 (2031)Artemis 8 (2032) CLPS VIPER (Nov 2024)IM-2 (2024) Lunar TrailblazerBlue Ghost (2024) Luna-Glob Luna 26 (2027)Luna 27 (2028)Luna 28 (2030)Luna 29 (2030s)Luna 30 (2030s)Luna 31 (2030s) CLEP Chang'e 6 (2024)Chang'e 7 (2026)Chang'e 8 (2028) Others Hakuto-R M2 (2024)DESTINY+ (2025)Beresheet 2 (2025)ispace M3 (2026)Lunar Pathfinder (2026)Cislunar Explorers (2020s)CU-E3 (2020s)MoonRanger (2020s)#dearMoon project (late 2020s)International Lunar Research Station (late 2020s) Proposed missions Robotic Lunar Polar Exploration MissionALINAArtemis-7Blue MoonBOLASGaratéa-LISOCHRONLunaNetLunar Crater Radio TelescopeMcCandlessMoon Diver Crewed DSE-AlphaBoeing Lunar LanderLockheed Martin Lunar LanderLunar Orbital Station Cancelled / concepts AltairBaden-Württemberg 1European Lunar ExplorerFirst Lunar OutpostInternational Lunar NetworkLEOLKLunar-ALunar LanderLunar Mission OneLunar ObserverLunokhod 3MoonLITEMoonRiseOrbitBeyondProject Harvest MoonProspectorResource ProspectorSELENE-2UkrselenaXL-1 Related Colonization of the MoonGoogle Lunar X PrizeList of lunar probesList of missions to the MoonList of artificial objects on the MoonList of species that have landed on the MoonLunar resourcesApollo 17 Moon miceMoon landing conspiracy theoriesThird-party evidence for Apollo Moon landingsApollo 11 anniversariesList of crewed lunar landers Missions are ordered by launch date. Crewed missions are in italics. vte Jupiter Outline of Jupiter Geography Atmosphere Great Red SpotMagnetosphereRingsJupiter's North PoleJupiter's South Pole NASA image of Jupiter Moons Inner moons MetisAdrasteaAmaltheaThebe Galilean moons IoEuropaGanymedeCallisto Irregular moons Himalia groupThemistoCarpoValetudoAnanke groupCarme groupPasiphae group Astronomy General Jupiter-crossing minor planetsSolar eclipses Trojans Greek campTrojan camp Impact events Comet Shoemaker–Levy 92009 Jupiter impact event2010 Jupiter impact event2016 Jupiter impact event Exploration and orbiting missions Current Juno Past CassiniGalileoNew HorizonsPioneer program Pioneer 10Pioneer 11UlyssesVoyager program Voyager 1Voyager 2 Future Jupiter Icy Moons Explorer (2023, en route)Europa Clipper (2024) Proposed Laplace-P (2023)Shensuo (2024)Io Volcano Observer (2026)Tianwen-4 (2029)Smara (2030) Related FictionMythologySailor Jupiter Category Solar System portal vte NASA planetary exploration programs Active Large 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For the company, see SpaceX. For broader coverage of this topic, see Exploration. Buzz Aldrin taking a core sample of the Moon during the Apollo 11 mission Self-portrait of Curiosity rover on Mars's surface Part of a series on Spaceflight History History of spaceflight Space Race Timeline of spaceflight Space probes Lunar missions Mars missions Applications Communications Earth observation Exploration Espionage Military Navigation Settlement Telescopes Tourism Spacecraft Robotic spacecraft Satellite Space probe Cargo spacecraft Crewed spacecraft Apollo LM Space capsules Space Shuttle Space stations Spaceplanes Vostok Space launch Spaceport Launch pad Expendable and reusable launch vehicles Escape velocity Non-rocket spacelaunch Spaceflight types Sub-orbital Orbital Interplanetary Interstellar Intergalactic List of space organizations Space agencies Space forces Companies Spaceflight portal vte Space exploration is the use of astronomy and space technology to explore outer space.[1] While the exploration of space is currently carried out mainly by astronomers with telescopes, its physical exploration is conducted both by uncrewed robotic space probes and human spaceflight. Space exploration, like its classical form astronomy, is one of the main sources for space science. While the observation of objects in space, known as astronomy, predates reliable recorded history, it was the development of large and relatively efficient rockets during the mid-twentieth century that allowed physical space exploration to become a reality. Common rationales for exploring space include advancing scientific research, national prestige, uniting different nations, ensuring the future survival of humanity, and developing military and strategic advantages against other countries.[2] The early era of space exploration was driven by a "Space Race" between the Soviet Union and the United States. A driving force of the start of space exploration was during the Cold War. After the ability to create nuclear weapons, the narrative of defense/offense left land and the power to control the air became the focus. Both the Soviet and the U.S. were fighting to prove their superiority in technology through exploring the unknown: space. In fact, the reason NASA was made was due to the response of Sputnik I.[3] The launch of the first human-made object to orbit Earth, the Soviet Union's Sputnik 1, on 4 October 1957, and the first Moon landing by the American Apollo 11 mission on 20 July 1969 are often taken as landmarks for this initial period. The Soviet space program achieved many of the first milestones, including the first living being in orbit in 1957, the first human spaceflight (Yuri Gagarin aboard Vostok 1) in 1961, the first spacewalk (by Alexei Leonov) on 18 March 1965, the first automatic landing on another celestial body in 1966, and the launch of the first space station (Salyut 1) in 1971. After the first 20 years of exploration, focus shifted from one-off flights to renewable hardware, such as the Space Shuttle program, and from competition to cooperation as with the International Space Station (ISS). With the substantial completion of the ISS[4] following STS-133 in March 2011, plans for space exploration by the U.S. remain in flux. Constellation, a Bush administration program for a return to the Moon by 2020[5] was judged inadequately funded and unrealistic by an expert review panel reporting in 2009.[6] The Obama administration proposed a revision of Constellation in 2010 to focus on the development of the capability for crewed missions beyond low Earth orbit (LEO), envisioning extending the operation of the ISS beyond 2020, transferring the development of launch vehicles for human crews from NASA to the private sector, and developing technology to enable missions to beyond LEO, such as Earth–Moon L1, the Moon, Earth–Sun L2, near-Earth asteroids, and Phobos or Mars orbit.[7] In the 2000s, China initiated a successful crewed spaceflight program while India launched Chandraayan 1, while the European Union and Japan have also planned future crewed space missions. China, Russia, and Japan have advocated crewed missions to the Moon during the 21st century, while the European Union has advocated crewed missions to both the Moon and Mars during the 20th and 21st century. History of exploration See also: History of astronomy, Discovery and exploration of the Solar System, Timeline of space exploration, Timeline of first orbital launches by country, and Outer space § Discovery V-2 Rocket in the Peenemünde Museum First telescopes The first telescope is said to have been invented in 1608 in the Netherlands by an eyeglass maker named Hans Lippershey, but their first recorded use in astronomy was by Galileo Galilei in 1609.[8] In 1668 Isaac Newton built his own reflecting telescope, the first fully functional telescope of this kind, and a landmark for future developments due to its superior features over the previous Galilean telescope.[9] A string of discoveries in the Solar System (and beyond) followed, then and in the next centuries: the mountains of the Moon, the phases of Venus, the main satellites of Jupiter and Saturn, the rings of Saturn, many comets, the asteroids, the new planets Uranus and Neptune, and many more satellites. The Orbiting Astronomical Observatory 2 was the first space telescope launched 1968,[10] but the launching of Hubble Space Telescope in 1990[11] set a milestone. As of 1 December 2022, there were 5,284 confirmed exoplanets discovered. The Milky Way is estimated to contain 100–400 billion stars[12] and more than 100 billion planets.[13] There are at least 2 trillion galaxies in the observable universe.[14][15] HD1 is the most distant known object from Earth, reported as 33.4 billion light-years away.[16][17][18][19][20][21] First outer space flights Model of Vostok spacecraft Apollo CSM in lunar orbit MW 18014 was a German V-2 rocket test launch that took place on 20 June 1944, at the Peenemünde Army Research Center in Peenemünde. It was the first man-made object to reach outer space, attaining an apogee of 176 kilometers,[22] which is well above the Kármán line.[23] It was a vertical test launch. Although the rocket reached space, it did not reach orbital velocity, and therefore returned to Earth in an impact, becoming the first sub-orbital spaceflight.[24] First object in orbit The first successful orbital launch was of the Soviet uncrewed Sputnik 1 ("Satellite 1") mission on 4 October 1957. The satellite weighed about 83 kg (183 lb), and is believed to have orbited Earth at a height of about 250 km (160 mi). It had two radio transmitters (20 and 40 MHz), which emitted "beeps" that could be heard by radios around the globe. Analysis of the radio signals was used to gather information about the electron density of the ionosphere, while temperature and pressure data was encoded in the duration of radio beeps. The results indicated that the satellite was not punctured by a meteoroid. Sputnik 1 was launched by an R-7 rocket. It burned up upon re-entry on 3 January 1958. First human outer space flight The first successful human spaceflight was Vostok 1 ("East 1"), carrying the 27-year-old Russian cosmonaut, Yuri Gagarin, on 12 April 1961. The spacecraft completed one orbit around the globe, lasting about 1 hour and 48 minutes. Gagarin's flight resonated around the world; it was a demonstration of the advanced Soviet space program and it opened an entirely new era in space exploration: human spaceflight. First astronomical body space explorations The first artificial object to reach another celestial body was Luna 2 reaching the Moon in 1959.[25] The first soft landing on another celestial body was performed by Luna 9 landing on the Moon on 3 February 1966.[26] Luna 10 became the first artificial satellite of the Moon, entering in a lunar orbit on 3 April 1966.[27] The first crewed landing on another celestial body was performed by Apollo 11 on 20 July 1969, landing on the Moon. There have been a total of six spacecraft with humans landing on the Moon starting from 1969 to the last human landing in 1972. The first interplanetary flyby was the 1961 Venera 1 flyby of Venus, though the 1962 Mariner 2 was the first flyby of Venus to return data (closest approach 34,773 kilometers). Pioneer 6 was the first satellite to orbit the Sun, launched on 16 December 1965. The other planets were first flown by in 1965 for Mars by Mariner 4, 1973 for Jupiter by Pioneer 10, 1974 for Mercury by Mariner 10, 1979 for Saturn by Pioneer 11, 1986 for Uranus by Voyager 2, 1989 for Neptune by Voyager 2. In 2015, the dwarf planets Ceres and Pluto were orbited by Dawn and passed by New Horizons, respectively. This accounts for flybys of each of the eight planets in the Solar System, the Sun, the Moon, and Ceres and Pluto (two of the five recognized dwarf planets). The first interplanetary surface mission to return at least limited surface data from another planet was the 1970 landing of Venera 7, which returned data to Earth for 23 minutes from Venus. In 1975 the Venera 9 was the first to return images from the surface of another planet, returning images from Venus. In 1971 the Mars 3 mission achieved the first soft landing on Mars returning data for almost 20 seconds. Later much longer duration surface missions were achieved, including over six years of Mars surface operation by Viking 1 from 1975 to 1982 and over two hours of transmission from the surface of Venus by Venera 13 in 1982, the longest ever Soviet planetary surface mission. Venus and Mars are the two planets outside of Earth on which humans have conducted surface missions with uncrewed robotic spacecraft. First space station Salyut 1 was the first space station of any kind, launched into low Earth orbit by the Soviet Union on 19 April 1971. The International Space Station is currently the largest and oldest of the 2 current fully functional space stations, inhabited continuously since the year 2000. The other, Tiangong space station built by China, is now fully crewed and operational. First interstellar space flight Voyager 1 became the first human-made object to leave the Solar System into interstellar space on 25 August 2012. The probe passed the heliopause at 121 AU to enter interstellar space.[28] Farthest from Earth The Apollo 13 flight passed the far side of the Moon at an altitude of 254 kilometers (158 miles; 137 nautical miles) above the lunar surface, and 400,171 km (248,655 mi) from Earth, marking the record for the farthest humans have ever traveled from Earth in 1970. As of 26 November 2022 Voyager 1 was at a distance of 159 AU (23.8 billion km; 14.8 billion mi) from Earth.[29] It is the most distant human-made object from Earth.[30] Targets of exploration Starting in the mid-20th century probes and then human mission were sent into Earth orbit, and then on to the Moon. Also, probes were sent throughout the known Solar System, and into Solar orbit. Uncrewed spacecraft have been sent into orbit around Saturn, Jupiter, Mars, Venus, and Mercury by the 21st century, and the most distance active spacecraft, Voyager 1 and 2 traveled beyond 100 times the Earth-Sun distance. The instruments were enough though that it is thought they have left the Sun's heliosphere, a sort of bubble of particles made in the Galaxy by the Sun's solar wind. The Sun The Sun is a major focus of space exploration. Being above the atmosphere in particular and Earth's magnetic field gives access to the solar wind and infrared and ultraviolet radiations that cannot reach Earth's surface. The Sun generates most space weather, which can affect power generation and transmission systems on Earth and interfere with, and even damage, satellites and space probes. Numerous spacecraft dedicated to observing the Sun, beginning with the Apollo Telescope Mount, have been launched and still others have had solar observation as a secondary objective. Parker Solar Probe, launched in 2018, will approach the Sun to within 1/9th the orbit of Mercury. Mercury Main article: Exploration of Mercury A MESSENGER image from 18,000 km showing a region about 500 km across (2008) Mercury remains the least explored of the Terrestrial planets. As of May 2013, the Mariner 10 and MESSENGER missions have been the only missions that have made close observations of Mercury. MESSENGER entered orbit around Mercury in March 2011, to further investigate the observations made by Mariner 10 in 1975 (Munsell, 2006b). A third mission to Mercury, scheduled to arrive in 2025, BepiColombo is to include two probes. BepiColombo is a joint mission between Japan and the European Space Agency. MESSENGER and BepiColombo are intended to gather complementary data to help scientists understand many of the mysteries discovered by Mariner 10's flybys. Flights to other planets within the Solar System are accomplished at a cost in energy, which is described by the net change in velocity of the spacecraft, or delta-v. Due to the relatively high delta-v to reach Mercury and its proximity to the Sun, it is difficult to explore and orbits around it are rather unstable. Venus Main article: Observations and explorations of Venus Venus was the first target of interplanetary flyby and lander missions and, despite one of the most hostile surface environments in the Solar System, has had more landers sent to it (nearly all from the Soviet Union) than any other planet in the Solar System. The first flyby was the 1961 Venera 1, though the 1962 Mariner 2 was the first flyby to successfully return data. Mariner 2 has been followed by several other flybys by multiple space agencies often as part of missions using a Venus flyby to provide a gravitational assist en route to other celestial bodies. In 1967 Venera 4 became the first probe to enter and directly examine the atmosphere of Venus. In 1970, Venera 7 became the first successful lander to reach the surface of Venus and by 1985 it had been followed by eight additional successful Soviet Venus landers which provided images and other direct surface data. Starting in 1975 with the Soviet orbiter Venera 9 some ten successful orbiter missions have been sent to Venus, including later missions which were able to map the surface of Venus using radar to pierce the obscuring atmosphere. Earth Main article: Earth observation satellite First television image of Earth from space, taken by TIROS-1 (1960) Space exploration has been used as a tool to understand Earth as a celestial object. Orbital missions can provide data for Earth that can be difficult or impossible to obtain from a purely ground-based point of reference. For example, the existence of the Van Allen radiation belts was unknown until their discovery by the United States' first artificial satellite, Explorer 1. These belts contain radiation trapped by Earth's magnetic fields, which currently renders construction of habitable space stations above 1000 km impractical. Following this early unexpected discovery, a large number of Earth observation satellites have been deployed specifically to explore Earth from a space-based perspective. These satellites have significantly contributed to the understanding of a variety of Earth-based phenomena. For instance, the hole in the ozone layer was found by an artificial satellite that was exploring Earth's atmosphere, and satellites have allowed for the discovery of archeological sites or geological formations that were difficult or impossible to otherwise identify. Moon Main article: Exploration of the Moon Apollo 16 LEM Orion, the Lunar Roving Vehicle and astronaut John Young (1972) The Moon was the first celestial body to be the object of space exploration. It holds the distinctions of being the first remote celestial object to be flown by, orbited, and landed upon by spacecraft, and the only remote celestial object ever to be visited by humans. In 1959 the Soviets obtained the first images of the far side of the Moon, never previously visible to humans. The U.S. exploration of the Moon began with the Ranger 4 impactor in 1962. Starting in 1966 the Soviets successfully deployed a number of landers to the Moon which were able to obtain data directly from the Moon's surface; just four months later, Surveyor 1 marked the debut of a successful series of U.S. landers. The Soviet uncrewed missions culminated in the Lunokhod program in the early 1970s, which included the first uncrewed rovers and also successfully brought lunar soil samples to Earth for study. This marked the first (and to date the only) automated return of extraterrestrial soil samples to Earth. Uncrewed exploration of the Moon continues with various nations periodically deploying lunar orbiters, and in 2008 the Indian Moon Impact Probe and in 2023 the Chandrayaan-3 of India became the first spacecraft to land on the lunar south pole. Crewed exploration of the Moon began in 1968 with the Apollo 8 mission that successfully orbited the Moon, the first time any extraterrestrial object was orbited by humans. In 1969, the Apollo 11 mission marked the first time humans set foot upon another world. Crewed exploration of the Moon did not continue for long. The Apollo 17 mission in 1972 marked the sixth landing and the most recent human visit. Artemis 2 is scheduled to complete a crewed flyby of the Moon in 2025, and Artemis 3 will perform the first lunar landing since Apollo 17 with it scheduled for launch no earlier than 2026. Robotic missions are still pursued vigorously. Mars Main article: Exploration of Mars Surface of Mars by the Spirit rover (2004) The exploration of Mars has been an important part of the space exploration programs of the Soviet Union (later Russia), the United States, Europe, Japan and India. Dozens of robotic spacecraft, including orbiters, landers, and rovers, have been launched toward Mars since the 1960s. These missions were aimed at gathering data about current conditions and answering questions about the history of Mars. The questions raised by the scientific community are expected to not only give a better appreciation of the Red Planet but also yield further insight into the past, and possible future, of Earth. The exploration of Mars has come at a considerable financial cost with roughly two-thirds of all spacecraft destined for Mars failing before completing their missions, with some failing before they even began. Such a high failure rate can be attributed to the complexity and large number of variables involved in an interplanetary journey, and has led researchers to jokingly speak of The Great Galactic Ghoul[31] which subsists on a diet of Mars probes. This phenomenon is also informally known as the "Mars Curse".[32] In contrast to overall high failure rates in the exploration of Mars, India has become the first country to achieve success of its maiden attempt. India's Mars Orbiter Mission (MOM)[33][34][35] is one of the least expensive interplanetary missions ever undertaken with an approximate total cost of ₹ 450 Crore (US$73 million).[36][37] The first mission to Mars by any Arab country has been taken up by the United Arab Emirates. Called the Emirates Mars Mission, it was launched on 19 July 2020 and went into orbit around Mars on 9 February 2021. The uncrewed exploratory probe was named "Hope Probe" and was sent to Mars to study its atmosphere in detail.[38] Phobos Main article: Exploration of Phobos The Russian space mission Fobos-Grunt, which launched on 9 November 2011 experienced a failure leaving it stranded in low Earth orbit.[39] It was to begin exploration of the Phobos and Martian circumterrestrial orbit, and study whether the moons of Mars, or at least Phobos, could be a "trans-shipment point" for spaceships traveling to Mars.[40] Asteroids Main article: Exploration of the asteroids Asteroid 4 Vesta, imaged by the Dawn spacecraft (2011) Until the advent of space travel, objects in the asteroid belt were merely pinpricks of light in even the largest telescopes, their shapes and terrain remaining a mystery. Several asteroids have now been visited by probes, the first of which was Galileo, which flew past two: 951 Gaspra in 1991, followed by 243 Ida in 1993. Both of these lay near enough to Galileo's planned trajectory to Jupiter that they could be visited at acceptable cost. The first landing on an asteroid was performed by the NEAR Shoemaker probe in 2000, following an orbital survey of the object, 433 Eros. The dwarf planet Ceres and the asteroid 4 Vesta, two of the three largest asteroids, were visited by NASA's Dawn spacecraft, launched in 2007. Hayabusa was a robotic spacecraft developed by the Japan Aerospace Exploration Agency to return a sample of material from the small near-Earth asteroid 25143 Itokawa to Earth for further analysis. Hayabusa was launched on 9 May 2003 and rendezvoused with Itokawa in mid-September 2005. After arriving at Itokawa, Hayabusa studied the asteroid's shape, spin, topography, color, composition, density, and history. In November 2005, it landed on the asteroid twice to collect samples. The spacecraft returned to Earth on 13 June 2010. Jupiter Main article: Exploration of Jupiter Tupan Patera on Io The exploration of Jupiter has consisted solely of a number of automated NASA spacecraft visiting the planet since 1973. A large majority of the missions have been "flybys", in which detailed observations are taken without the probe landing or entering orbit; such as in Pioneer and Voyager programs. The Galileo and Juno spacecraft are the only spacecraft to have entered the planet's orbit. As Jupiter is believed to have only a relatively small rocky core and no real solid surface, a landing mission is precluded. Reaching Jupiter from Earth requires a delta-v of 9.2 km/s,[41] which is comparable to the 9.7 km/s delta-v needed to reach low Earth orbit.[42] Fortunately, gravity assists through planetary flybys can be used to reduce the energy required at launch to reach Jupiter, albeit at the cost of a significantly longer flight duration.[41] Jupiter has 95 known moons, many of which have relatively little known information about them. Saturn Main article: Exploration of Saturn Saturn has been explored only through uncrewed spacecraft launched by NASA, including one mission (Cassini–Huygens) planned and executed in cooperation with other space agencies. These missions consist of flybys in 1979 by Pioneer 11, in 1980 by Voyager 1, in 1982 by Voyager 2 and an orbital mission by the Cassini spacecraft, which lasted from 2004 until 2017. Saturn has at least 62 known moons, although the exact number is debatable since Saturn's rings are made up of vast numbers of independently orbiting objects of varying sizes. The largest of the moons is Titan, which holds the distinction of being the only moon in the Solar System with an atmosphere denser and thicker than that of Earth. Titan holds the distinction of being the only object in the Outer Solar System that has been explored with a lander, the Huygens probe deployed by the Cassini spacecraft. Uranus Main article: Exploration of Uranus The exploration of Uranus has been entirely through the Voyager 2 spacecraft, with no other visits currently planned. Given its axial tilt of 97.77°, with its polar regions exposed to sunlight or darkness for long periods, scientists were not sure what to expect at Uranus. The closest approach to Uranus occurred on 24 January 1986. Voyager 2 studied the planet's unique atmosphere and magnetosphere. Voyager 2 also examined its ring system and the moons of Uranus including all five of the previously known moons, while discovering an additional ten previously unknown moons. Images of Uranus proved to have a very uniform appearance, with no evidence of the dramatic storms or atmospheric banding evident on Jupiter and Saturn. Great effort was required to even identify a few clouds in the images of the planet. The magnetosphere of Uranus, however, proved to be unique, being profoundly affected by the planet's unusual axial tilt. In contrast to the bland appearance of Uranus itself, striking images were obtained of the Moons of Uranus, including evidence that Miranda had been unusually geologically active. Neptune Main article: Exploration of Neptune The exploration of Neptune began with 25 August 1989 Voyager 2 flyby, the sole visit to the system as of 2024. The possibility of a Neptune Orbiter has been discussed, but no other missions have been given serious thought. Although the extremely uniform appearance of Uranus during Voyager 2's visit in 1986 had led to expectations that Neptune would also have few visible atmospheric phenomena, the spacecraft found that Neptune had obvious banding, visible clouds, auroras, and even a conspicuous anticyclone storm system rivaled in size only by Jupiter's Great Red Spot. Neptune also proved to have the fastest winds of any planet in the Solar System, measured as high as 2,100 km/h.[43] Voyager 2 also examined Neptune's ring and moon system. It discovered 900 complete rings and additional partial ring "arcs" around Neptune. In addition to examining Neptune's three previously known moons, Voyager 2 also discovered five previously unknown moons, one of which, Proteus, proved to be the last largest moon in the system. Data from Voyager 2 supported the view that Neptune's largest moon, Triton, is a captured Kuiper belt object.[44] Pluto Main article: Pluto § Exploration The dwarf planet Pluto presents significant challenges for spacecraft because of its great distance from Earth (requiring high velocity for reasonable trip times) and small mass (making capture into orbit very difficult at present). Voyager 1 could have visited Pluto, but controllers opted instead for a close flyby of Saturn's moon Titan, resulting in a trajectory incompatible with a Pluto flyby. Voyager 2 never had a plausible trajectory for reaching Pluto.[45] After an intense political battle, a mission to Pluto dubbed New Horizons was granted funding from the United States government in 2003.[46] New Horizons was launched successfully on 19 January 2006. In early 2007 the craft made use of a gravity assist from Jupiter. Its closest approach to Pluto was on 14 July 2015; scientific observations of Pluto began five months prior to closest approach and continued for 16 days after the encounter. Kuiper Belt Objects The New Horizons mission also did a flyby of the small planetesimal Arrokoth, in the Kuiper belt, in 2019. This was its first extended mission.[47] Comets Main article: List of missions to comets Comet 103P/Hartley (2010) Although many comets have been studied from Earth sometimes with centuries-worth of observations, only a few comets have been closely visited. In 1985, the International Cometary Explorer conducted the first comet fly-by (21P/Giacobini-Zinner) before joining the Halley Armada studying the famous comet. The Deep Impact probe smashed into 9P/Tempel to learn more about its structure and composition and the Stardust mission returned samples of another comet's tail. The Philae lander successfully landed on Comet Churyumov–Gerasimenko in 2014 as part of the broader Rosetta mission. Deep space exploration Main article: Deep space exploration This high-resolution image of the Hubble Ultra Deep Field includes galaxies of various ages, sizes, shapes, and colors. The smallest, reddest galaxies, are some of the most distant galaxies to have been imaged by an optical telescope. Deep space exploration is the branch of astronomy, astronautics and space technology that is involved with the exploration of distant regions of outer space.[48] Physical exploration of space is conducted both by human spaceflights (deep-space astronautics) and by robotic spacecraft. Some of the best candidates for future deep space engine technologies include anti-matter, nuclear power and beamed propulsion.[49] The latter, beamed propulsion, appears to be the best candidate for deep space exploration presently available, since it uses known physics and known technology that is being developed for other purposes.[50] Future of space exploration Main article: Future of space exploration Concept art for a NASA Vision mission Artistic image of a rocket lifting from a Saturn moon Breakthrough Starshot Main article: Breakthrough Starshot Breakthrough Starshot is a research and engineering project by the Breakthrough Initiatives to develop a proof-of-concept fleet of light sail spacecraft named StarChip,[51] to be capable of making the journey to the Alpha Centauri star system 4.37 light-years away. It was founded in 2016 by Yuri Milner, Stephen Hawking, and Mark Zuckerberg.[52][53] Asteroids Main article: Exploration of the asteroids An article in science magazine Nature suggested the use of asteroids as a gateway for space exploration, with the ultimate destination being Mars. In order to make such an approach viable, three requirements need to be fulfilled: first, "a thorough asteroid survey to find thousands of nearby bodies suitable for astronauts to visit"; second, "extending flight duration and distance capability to ever-increasing ranges out to Mars"; and finally, "developing better robotic vehicles and tools to enable astronauts to explore an asteroid regardless of its size, shape or spin". Furthermore, using asteroids would provide astronauts with protection from galactic cosmic rays, with mission crews being able to land on them without great risk to radiation exposure. James Webb Space Telescope Main article: James Webb Space Telescope The James Webb Space Telescope (JWST or "Webb") is a space telescope that is the successor to the Hubble Space Telescope.[54][55] The JWST will provide greatly improved resolution and sensitivity over the Hubble, and will enable a broad range of investigations across the fields of astronomy and cosmology, including observing some of the most distant events and objects in the universe, such as the formation of the first galaxies. Other goals include understanding the formation of stars and planets, and direct imaging of exoplanets and novas.[56] The primary mirror of the JWST, the Optical Telescope Element, is composed of 18 hexagonal mirror segments made of gold-plated beryllium which combine to create a 6.5-meter (21 ft; 260 in) diameter mirror that is much larger than the Hubble's 2.4-meter (7.9 ft; 94 in) mirror. Unlike the Hubble, which observes in the near ultraviolet, visible, and near infrared (0.1 to 1 μm) spectra, the JWST will observe in a lower frequency range, from long-wavelength visible light through mid-infrared (0.6 to 27 μm), which will allow it to observe high redshift objects that are too old and too distant for the Hubble to observe.[57] The telescope must be kept very cold in order to observe in the infrared without interference, so it will be deployed in space near the Earth–Sun L2 Lagrangian point, and a large sunshield made of silicon- and aluminum-coated Kapton will keep its mirror and instruments below 50 K (−220 °C; −370 °F).[58] Artemis program Main article: Artemis program The Artemis program is an ongoing crewed spaceflight program carried out by NASA, U.S. commercial spaceflight companies, and international partners such as ESA,[59] with the goal of landing "the first woman and the next man" on the Moon, specifically at the lunar south pole region by 2024. Artemis would be the next step towards the long-term goal of establishing a sustainable presence on the Moon, laying the foundation for private companies to build a lunar economy, and eventually sending humans to Mars. In 2017, the lunar campaign was authorized by Space Policy Directive 1, utilizing various ongoing spacecraft programs such as Orion, the Lunar Gateway, Commercial Lunar Payload Services, and adding an undeveloped crewed lander. The Space Launch System will serve as the primary launch vehicle for Orion, while commercial launch vehicles are planned for use to launch various other elements of the campaign.[60] NASA requested $1.6 billion in additional funding for Artemis for fiscal year 2020,[61] while the Senate Appropriations Committee requested from NASA a five-year budget profile[62] which is needed for evaluation and approval by Congress.[63][64] Rationales Main article: Space advocacy Astronaut Buzz Aldrin had a personal Communion service when he first arrived on the surface of the Moon. The research that is conducted by national space exploration agencies, such as NASA and Roscosmos, is one of the reasons supporters cite to justify government expenses. Economic analyses of the NASA programs often showed ongoing economic benefits (such as NASA spin-offs), generating many times the revenue of the cost of the program.[65] It is also argued that space exploration would lead to the extraction of resources on other planets and especially asteroids, which contain billions of dollars worth of minerals and metals. Such expeditions could generate a lot of revenue.[66] In addition, it has been argued that space exploration programs help inspire youth to study in science and engineering.[67] Space exploration also gives scientists the ability to perform experiments in other settings and expand humanity's knowledge.[68] Another claim is that space exploration is a necessity to mankind and that staying on Earth will lead to extinction. Some of the reasons are lack of natural resources, comets, nuclear war, and worldwide epidemic. Stephen Hawking, renowned British theoretical physicist, said that "I don't think the human race will survive the next thousand years, unless we spread into space. There are too many accidents that can befall life on a single planet. But I'm an optimist. We will reach out to the stars."[69] Arthur C. Clarke (1950) presented a summary of motivations for the human exploration of space in his non-fiction semi-technical monograph Interplanetary Flight.[70] He argued that humanity's choice is essentially between expansion off Earth into space, versus cultural (and eventually biological) stagnation and death. These motivations could be attributed to one of the first rocket scientists in NASA, Wernher von Braun, and his vision of humans moving beyond Earth. The basis of this plan was to: Develop multi-stage rockets capable of placing satellites, animals, and humans in space. Development of large, winged reusable spacecraft capable of carrying humans and equipment into Earth orbit in a way that made space access routine and cost-effective. Construction of a large, permanently occupied space station to be used as a platform both to observe Earth and from which to launch deep space expeditions. Launching the first human flights around the Moon, leading to the first landings of humans on the Moon, with the intent of exploring that body and establishing permanent lunar bases. Assembly and fueling of spaceships in Earth orbit for the purpose of sending humans to Mars with the intent of eventually colonizing that planet.[71] Known as the Von Braun Paradigm, the plan was formulated to lead humans in the exploration of space. Von Braun's vision of human space exploration served as the model for efforts in space exploration well into the twenty-first century, with NASA incorporating this approach into the majority of their projects.[71] The steps were followed out of order, as seen by the Apollo program reaching the moon before the space shuttle program was started, which in turn was used to complete the International Space Station. Von Braun's Paradigm formed NASA's drive for human exploration, in the hopes that humans discover the far reaches of the universe. NASA has produced a series of public service announcement videos supporting the concept of space exploration.[72] Overall, the public remains largely supportive of both crewed and uncrewed space exploration. According to an Associated Press Poll conducted in July 2003, 71% of U.S. citizens agreed with the statement that the space program is "a good investment", compared to 21% who did not.[73] Human nature Space advocacy and space policy[74] regularly invokes exploration as a human nature.[75] Topics Main articles: Space science and Human presence in space Spaceflight Main articles: Spaceflight and Astronautics Delta-v's in km/s for various orbital maneuvers Spaceflight is the use of space technology to achieve the flight of spacecraft into and through outer space. Spaceflight is used in space exploration, and also in commercial activities like space tourism and satellite telecommunications. Additional non-commercial uses of spaceflight include space observatories, reconnaissance satellites and other Earth observation satellites. A spaceflight typically begins with a rocket launch, which provides the initial thrust to overcome the force of gravity and propels the spacecraft from the surface of Earth. Once in space, the motion of a spacecraft—both when unpropelled and when under propulsion—is covered by the area of study called astrodynamics. Some spacecraft remain in space indefinitely, some disintegrate during atmospheric reentry, and others reach a planetary or lunar surface for landing or impact. Satellites Main article: Satellite Satellites are used for a large number of purposes. Common types include military (spy) and civilian Earth observation satellites, communication satellites, navigation satellites, weather satellites, and research satellites. Space stations and human spacecraft in orbit are also satellites. Commercialization of space Main article: Commercialization of space The commercialization of space first started out with the launching of private satellites by NASA or other space agencies. Current examples of the commercial satellite use of space include satellite navigation systems, satellite television and satellite radio. The next step of commercialization of space was seen as human spaceflight. Flying humans safely to and from space had become routine to NASA.[76] Reusable spacecraft were an entirely new engineering challenge, something only seen in novels and films like Star Trek and War of the Worlds. Great names like Buzz Aldrin supported the use of making a reusable vehicle like the space shuttle. Aldrin held that reusable spacecraft were the key in making space travel affordable, stating that the use of "passenger space travel is a huge potential market big enough to justify the creation of reusable launch vehicles".[77] How can the public go against the words of one of America's best known heroes in space exploration? After all exploring space is the next great expedition, following the example of Lewis and Clark.Space tourism is the next step reusable vehicles in the commercialization of space. The purpose of this form of space travel is used by individuals for the purpose of personal pleasure. Private spaceflight companies such as SpaceX and Blue Origin, and commercial space stations such as the Axiom Space and the Bigelow Commercial Space Station have dramatically changed the landscape of space exploration, and will continue to do so in the near future. Alien life Main articles: Astrobiology and Extraterrestrial life Astrobiology is the interdisciplinary study of life in the universe, combining aspects of astronomy, biology and geology.[78] It is focused primarily on the study of the origin, distribution and evolution of life. It is also known as exobiology (from Greek: έξω, exo, "outside").[79][80][81] The term "Xenobiology" has been used as well, but this is technically incorrect because its terminology means "biology of the foreigners".[82] Astrobiologists must also consider the possibility of life that is chemically entirely distinct from any life found on Earth.[83] In the Solar System some of the prime locations for current or past astrobiology are on Enceladus, Europa, Mars, and Titan.[84] Human spaceflight and habitation Main articles: Human spaceflight, Bioastronautics, Effect of spaceflight on the human body, Space medicine, Space architecture, Space station, Space habitat (facility), and Space habitat (settlement) Crew quarters on Zvezda, the base ISS crew module To date, the longest human occupation of space is the International Space Station which has been in continuous use for 23 years, 150 days. Valeri Polyakov's record single spaceflight of almost 438 days aboard the Mir space station has not been surpassed. The health effects of space have been well documented through years of research conducted in the field of aerospace medicine. Analog environments similar to those one may experience in space travel (like deep sea submarines) have been used in this research to further explore the relationship between isolation and extreme environments.[85] It is imperative that the health of the crew be maintained as any deviation from baseline may compromise the integrity of the mission as well as the safety of the crew, hence the reason why astronauts must endure rigorous medical screenings and tests prior to embarking on any missions. However, it does not take long for the environmental dynamics of spaceflight to commence its toll on the human body; for example, space motion sickness (SMS) – a condition which affects the neurovestibular system and culminates in mild to severe signs and symptoms such as vertigo, dizziness, fatigue, nausea, and disorientation – plagues almost all space travelers within their first few days in orbit.[85] Space travel can also have a profound impact on the psyche of the crew members as delineated in anecdotal writings composed after their retirement. Space travel can adversely affect the body's natural biological clock (circadian rhythm); sleep patterns causing sleep deprivation and fatigue; and social interaction; consequently, residing in a Low Earth Orbit (LEO) environment for a prolonged amount of time can result in both mental and physical exhaustion.[85] Long-term stays in space reveal issues with bone and muscle loss in low gravity, immune system suppression, and radiation exposure. The lack of gravity causes fluid to rise upward which can cause pressure to build up in the eye, resulting in vision problems; the loss of bone minerals and densities; cardiovascular deconditioning; and decreased endurance and muscle mass.[86] Radiation is an insidious health hazard to space travelers as it is invisible and can cause cancer. When above the Earth's magnetic field spacecraft are no longer protected from the sun's radiation; the danger of radiation is even more potent in deep space. The hazards of radiation can be ameliorated through protective shielding on the spacecraft, alerts, and dosimetry.[87] Fortunately, with new and rapidly evolving technological advancements, those in Mission Control are able to monitor the health of their astronauts more closely utilizing telemedicine. One may not be able to completely evade the physiological effects of space flight, but they can be mitigated. For example, medical systems aboard space vessels such as the International Space Station (ISS) are well equipped and designed to counteract the effects of lack of gravity and weightlessness; on-board treadmills can help prevent muscle loss and reduce the risk of developing premature osteoporosis.[85][87] Additionally, a crew medical officer is appointed for each ISS mission and a flight surgeon is available 24/7 via the ISS Mission Control Center located in Houston, Texas.[87] Although the interactions are intended to take place in real time, communications between the space and terrestrial crew may become delayed – sometimes by as much as 20 minutes[87] – as their distance from each other increases when the spacecraft moves further out of LEO; because of this the crew are trained and need to be prepared to respond to any medical emergencies that may arise on the vessel as the ground crew are hundreds of miles away. As one can see, travelling and possibly living in space poses many challenges. Many past and current concepts for the continued exploration and colonization of space focus on a return to the Moon as a "stepping stone" to the other planets, especially Mars. At the end of 2006 NASA announced they were planning to build a permanent Moon base with continual presence by 2024.[88] Beyond the technical factors that could make living in space more widespread, it has been suggested that the lack of private property, the inability or difficulty in establishing property rights in space, has been an impediment to the development of space for human habitation. Since the advent of space technology in the latter half of the twentieth century, the ownership of property in space has been murky, with strong arguments both for and against. In particular, the making of national territorial claims in outer space and on celestial bodies has been specifically proscribed by the Outer Space Treaty, which had been, as of 2012, ratified by all spacefaring nations.[89] Space colonization, also called space settlement and space humanization, would be the permanent autonomous (self-sufficient) human habitation of locations outside Earth, especially of natural satellites or planets such as the Moon or Mars, using significant amounts of in-situ resource utilization. Human representation and participation See also: Space law Participation and representation of humanity in space is an issue ever since the first phase of space exploration.[90] Some rights of non-spacefaring countries have been mostly secured through international space law, declaring space the "province of all mankind", understanding spaceflight as its resource, though sharing of space for all humanity is still criticized as imperialist and lacking.[90] Additionally to international inclusion, the inclusion of women and people of colour has also been lacking. To reach a more inclusive spaceflight some organizations like the Justspace Alliance[90] and IAU featured Inclusive Astronomy[91] have been formed in recent years. Women Main article: Women in space The first woman to go to space was Valentina Tereshkova. She flew in 1963 but it was not until the 1980s that another woman entered space again. All astronauts were required to be military test pilots at the time and women were not able to join this career, this is one reason for the delay in allowing women to join space crews.[citation needed] After the rule changed, Svetlana Savitskaya became the second woman to go to space, she was also from the Soviet Union. Sally Ride became the next woman in space and the first woman to fly to space through the United States program. Since then, eleven other countries have allowed women astronauts. The first all-female space walk occurred in 2018, including Christina Koch and Jessica Meir. They had both previously participated in space walks with NASA. The first woman to go to the Moon is planned for 2024. Despite these developments women are still underrepresented among astronauts and especially cosmonauts. Issues that block potential applicants from the programs, and limit the space missions they are able to go on, include: agencies limiting women to half as much time in space than men, arguing with unresearched potential risks for cancer.[92] a lack of space suits sized appropriately for female astronauts.[93] Art See also: Space art § Art in space Artistry in and from space ranges from signals, capturing and arranging material like Yuri Gagarin's selfie in space or the image The Blue Marble, over drawings like the first one in space by cosmonaut and artist Alexei Leonov, music videos like Chris Hadfield's cover of Space Oddity on board the ISS, to permanent installations on celestial bodies like on the Moon. See also Spaceflight portal Main article: Outline of space exploration Discovery and exploration of the Solar System Spacecraft propulsion List of crewed spacecraft List of missions to Mars List of missions to the outer planets List of landings on extraterrestrial bodies List of spaceflight records Robotic space exploration programs Robotic spacecraft Timeline of planetary exploration Landings on other planets Pioneer program Luna program Zond program Venera program Mars probe program Ranger program Mariner program Surveyor program Viking program Voyager program Vega program Phobos program Discovery program Chandrayaan Program Mangalyaan Program Chang'e Program Private Astrobotic Technology Program Living in space Interplanetary contamination Animals in space Animals in space Monkeys in space Russian space dogs Humans in space Astronauts List of human spaceflights List of human spaceflights by program Vostok program Mercury program Voskhod program Gemini program Soyuz program Apollo program Salyut program Skylab Space Shuttle program Mir International Space Station Vision for Space Exploration Aurora Programme Tier One Effect of spaceflight on the human body Space architecture Research station – Facility for scientific research Space observatory – Instrument in space to study astronomical objects Space archaeology flexible path destinations set Recent and future developments Commercial astronauts Artemis program Energy development Exploration of Mars Space tourism Private spaceflight Space colonization Interstellar spaceflight Deep space exploration Human outpost Mars to Stay NewSpace NASA lunar outpost concepts Other List of spaceflights Timeline of Solar System exploration List of artificial objects on extra-terrestrial surfaces Space station Space telescope Sample return mission Atmospheric reentry Space and survival List of spaceflight-related accidents and incidents Religion in space Militarisation of space French space program Russian explorers U.S. space exploration history on U.S. stamps Deep-sea exploration Arctic exploration Criticism of space exploration References "How Space is Explored". 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An overview of the history of space exploration and predictions for the future. External links Wikiquote has quotations related to Space exploration. Wikimedia Commons has media related to Space exploration. 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Click here for more information. Page semi-protected From Wikipedia, the free encyclopedia This article is about the scientific study of celestial objects. For other uses, see Astronomy (disambiguation). Not to be confused with astrology, a pseudoscience. The Paranal Observatory of European Southern Observatory shooting a laser guide star to the Galactic Center Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, meteoroids, asteroids, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates beyond Earth's atmosphere. Cosmology is a branch of astronomy that studies the universe as a whole. Astronomy is one of the oldest natural sciences. The early civilizations in recorded history made methodical observations of the night sky. These include the Egyptians, Babylonians, Greeks, Indians, Chinese, Maya, and many ancient indigenous peoples of the Americas. In the past, astronomy included disciplines as diverse as astrometry, celestial navigation, observational astronomy, and the making of calendars. Professional astronomy is split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects. This data is then analyzed using basic principles of physics. Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. These two fields complement each other. Theoretical astronomy seeks to explain observational results and observations are used to confirm theoretical results. Astronomy is one of the few sciences in which amateurs play an active role. This is especially true for the discovery and observation of transient events. Amateur astronomers have helped with many important discoveries, such as finding new comets. Etymology Astronomical Observatory, New South Wales, Australia 1873 19th-century Quito Astronomical Observatory is located 12 minutes south of the Equator in Quito, Ecuador.[1] Astronomy (from the Greek ἀστρονομία from ἄστρον astron, "star" and -νομία -nomia from νόμος nomos, "law" or "culture") means "law of the stars" (or "culture of the stars" depending on the translation). Astronomy should not be confused with astrology, the belief system which claims that human affairs are correlated with the positions of celestial objects.[2] Although the two fields share a common origin, they are now entirely distinct.[3] Use of terms "astronomy" and "astrophysics" "Astronomy" and "astrophysics" are synonyms.[4][5][6] Based on strict dictionary definitions, "astronomy" refers to "the study of objects and matter outside the Earth's atmosphere and of their physical and chemical properties",[7] while "astrophysics" refers to the branch of astronomy dealing with "the behavior, physical properties, and dynamic processes of celestial objects and phenomena".[8] In some cases, as in the introduction of the introductory textbook The Physical Universe by Frank Shu, "astronomy" may be used to describe the qualitative study of the subject, whereas "astrophysics" is used to describe the physics-oriented version of the subject.[9] However, since most modern astronomical research deals with subjects related to physics, modern astronomy could actually be called astrophysics.[4] Some fields, such as astrometry, are purely astronomy rather than also astrophysics. Various departments in which scientists carry out research on this subject may use "astronomy" and "astrophysics", partly depending on whether the department is historically affiliated with a physics department,[5] and many professional astronomers have physics rather than astronomy degrees.[6] Some titles of the leading scientific journals in this field include The Astronomical Journal, The Astrophysical Journal, and Astronomy & Astrophysics. History Main article: History of astronomy For a chronological guide, see Timeline of astronomy. Further information: Archaeoastronomy and List of astronomers A celestial map from the 17th century, by the Dutch cartographer Frederik de Wit. Ancient times In early historic times, astronomy only consisted of the observation and predictions of the motions of objects visible to the naked eye. In some locations, early cultures assembled massive artifacts that may have had some astronomical purpose. In addition to their ceremonial uses, these observatories could be employed to determine the seasons, an important factor in knowing when to plant crops and in understanding the length of the year.[10] Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye. As civilizations developed, most notably in Egypt, Mesopotamia, Greece, Persia, India, China, and Central America, astronomical observatories were assembled and ideas on the nature of the Universe began to develop. Most early astronomy consisted of mapping the positions of the stars and planets, a science now referred to as astrometry. From these observations, early ideas about the motions of the planets were formed, and the nature of the Sun, Moon and the Earth in the Universe were explored philosophically. The Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. This is known as the geocentric model of the Universe, or the Ptolemaic system, named after Ptolemy.[11] The Suryaprajnaptisūtra, a 6th-century BC astronomy text of Jains at The Schoyen Collection, London. Above: its manuscript from c. 1500 AD.[12] A particularly important early development was the beginning of mathematical and scientific astronomy, which began among the Babylonians, who laid the foundations for the later astronomical traditions that developed in many other civilizations.[13] The Babylonians discovered that lunar eclipses recurred in a repeating cycle known as a saros.[14] Greek equatorial sundial, Alexandria on the Oxus, present-day Afghanistan 3rd–2nd century BC. Following the Babylonians, significant advances in astronomy were made in ancient Greece and the Hellenistic world. Greek astronomy is characterized from the start by seeking a rational, physical explanation for celestial phenomena.[15] In the 3rd century BC, Aristarchus of Samos estimated the size and distance of the Moon and Sun, and he proposed a model of the Solar System where the Earth and planets rotated around the Sun, now called the heliocentric model.[16] In the 2nd century BC, Hipparchus discovered precession, calculated the size and distance of the Moon and invented the earliest known astronomical devices such as the astrolabe.[17] Hipparchus also created a comprehensive catalog of 1020 stars, and most of the constellations of the northern hemisphere derive from Greek astronomy.[18] The Antikythera mechanism (c. 150–80 BC) was an early analog computer designed to calculate the location of the Sun, Moon, and planets for a given date. Technological artifacts of similar complexity did not reappear until the 14th century, when mechanical astronomical clocks appeared in Europe.[19] Middle Ages Medieval Europe housed a number of important astronomers. Richard of Wallingford (1292–1336) made major contributions to astronomy and horology, including the invention of the first astronomical clock, the Rectangulus which allowed for the measurement of angles between planets and other astronomical bodies, as well as an equatorium called the Albion which could be used for astronomical calculations such as lunar, solar and planetary longitudes and could predict eclipses. Nicole Oresme (1320–1382) and Jean Buridan (1300–1361) first discussed evidence for the rotation of the Earth, furthermore, Buridan also developed the theory of impetus (predecessor of the modern scientific theory of inertia) which was able to show planets were capable of motion without the intervention of angels.[20] Georg von Peuerbach (1423–1461) and Regiomontanus (1436–1476) helped make astronomical progress instrumental to Copernicus's development of the heliocentric model decades later. Astronomy flourished in the Islamic world and other parts of the world. This led to the emergence of the first astronomical observatories in the Muslim world by the early 9th century.[21][22][23] In 964, the Andromeda Galaxy, the largest galaxy in the Local Group, was described by the Persian Muslim astronomer Abd al-Rahman al-Sufi in his Book of Fixed Stars.[24] The SN 1006 supernova, the brightest apparent magnitude stellar event in recorded history, was observed by the Egyptian Arabic astronomer Ali ibn Ridwan and Chinese astronomers in 1006. Iranian scholar Al-Biruni observed that, contrary to Ptolemy, the Sun's apogee (highest point in the heavens) was mobile, not fixed.[25] Some of the prominent Islamic (mostly Persian and Arab) astronomers who made significant contributions to the science include Al-Battani, Thebit, Abd al-Rahman al-Sufi, Biruni, Abū Ishāq Ibrāhīm al-Zarqālī, Al-Birjandi, and the astronomers of the Maragheh and Samarkand observatories. Astronomers during that time introduced many Arabic names now used for individual stars.[26][27] It is also believed that the ruins at Great Zimbabwe and Timbuktu[28] may have housed astronomical observatories.[29] In Post-classical West Africa, Astronomers studied the movement of stars and relation to seasons, crafting charts of the heavens as well as precise diagrams of orbits of the other planets based on complex mathematical calculations. Songhai historian Mahmud Kati documented a meteor shower in August 1583.[30][31] Europeans had previously believed that there had been no astronomical observation in sub-Saharan Africa during the pre-colonial Middle Ages, but modern discoveries show otherwise.[32][33][34][35] For over six centuries (from the recovery of ancient learning during the late Middle Ages into the Enlightenment), the Roman Catholic Church gave more financial and social support to the study of astronomy than probably all other institutions. Among the Church's motives was finding the date for Easter.[36] Scientific revolution Galileo's sketches and observations of the Moon revealed that the surface was mountainous. An astronomical chart from an early scientific manuscript, c. 1000. During the Renaissance, Nicolaus Copernicus proposed a heliocentric model of the solar system. His work was defended by Galileo Galilei and expanded upon by Johannes Kepler. Kepler was the first to devise a system that correctly described the details of the motion of the planets around the Sun. However, Kepler did not succeed in formulating a theory behind the laws he wrote down.[37] It was Isaac Newton, with his invention of celestial dynamics and his law of gravitation, who finally explained the motions of the planets. Newton also developed the reflecting telescope.[38] Improvements in the size and quality of the telescope led to further discoveries. The English astronomer John Flamsteed catalogued over 3000 stars,[39] More extensive star catalogues were produced by Nicolas Louis de Lacaille. The astronomer William Herschel made a detailed catalog of nebulosity and clusters, and in 1781 discovered the planet Uranus, the first new planet found.[40] During the 18–19th centuries, the study of the three-body problem by Leonhard Euler, Alexis Claude Clairaut, and Jean le Rond d'Alembert led to more accurate predictions about the motions of the Moon and planets. This work was further refined by Joseph-Louis Lagrange and Pierre Simon Laplace, allowing the masses of the planets and moons to be estimated from their perturbations.[41] Significant advances in astronomy came about with the introduction of new technology, including the spectroscope and photography. Joseph von Fraunhofer discovered about 600 bands in the spectrum of the Sun in 1814–15, which, in 1859, Gustav Kirchhoff ascribed to the presence of different elements. Stars were proven to be similar to the Earth's own Sun, but with a wide range of temperatures, masses, and sizes.[26] The existence of the Earth's galaxy, the Milky Way, as its own group of stars was only proved in the 20th century, along with the existence of "external" galaxies. The observed recession of those galaxies led to the discovery of the expansion of the Universe.[42] Theoretical astronomy led to speculations on the existence of objects such as black holes and neutron stars, which have been used to explain such observed phenomena as quasars, pulsars, blazars, and radio galaxies. Physical cosmology made huge advances during the 20th century. In the early 1900s the model of the Big Bang theory was formulated, heavily evidenced by cosmic microwave background radiation, Hubble's law, and the cosmological abundances of elements. Space telescopes have enabled measurements in parts of the electromagnetic spectrum normally blocked or blurred by the atmosphere.[43] In February 2016, it was revealed that the LIGO project had detected evidence of gravitational waves in the previous September.[44][45] Observational astronomy Main article: Observational astronomy The main source of information about celestial bodies and other objects is visible light, or more generally electromagnetic radiation.[46] Observational astronomy may be categorized according to the corresponding region of the electromagnetic spectrum on which the observations are made. Some parts of the spectrum can be observed from the Earth's surface, while other parts are only observable from either high altitudes or outside the Earth's atmosphere. Specific information on these subfields is given below. Radio astronomy The Very Large Array in New Mexico, an example of a radio telescope Main article: Radio astronomy Radio astronomy uses radiation with wavelengths greater than approximately one millimeter, outside the visible range.[47] Radio astronomy is different from most other forms of observational astronomy in that the observed radio waves can be treated as waves rather than as discrete photons. Hence, it is relatively easier to measure both the amplitude and phase of radio waves, whereas this is not as easily done at shorter wavelengths.[47] Although some radio waves are emitted directly by astronomical objects, a product of thermal emission, most of the radio emission that is observed is the result of synchrotron radiation, which is produced when electrons orbit magnetic fields.[47] Additionally, a number of spectral lines produced by interstellar gas, notably the hydrogen spectral line at 21 cm, are observable at radio wavelengths.[9][47] A wide variety of other objects are observable at radio wavelengths, including supernovae, interstellar gas, pulsars, and active galactic nuclei.[9][47] Infrared astronomy ALMA Observatory is one of the highest observatory sites on Earth. Atacama, Chile.[48] Main article: Infrared astronomy Infrared astronomy is founded on the detection and analysis of infrared radiation, wavelengths longer than red light and outside the range of our vision. The infrared spectrum is useful for studying objects that are too cold to radiate visible light, such as planets, circumstellar disks or nebulae whose light is blocked by dust. The longer wavelengths of infrared can penetrate clouds of dust that block visible light, allowing the observation of young stars embedded in molecular clouds and the cores of galaxies. Observations from the Wide-field Infrared Survey Explorer (WISE) have been particularly effective at unveiling numerous galactic protostars and their host star clusters.[49][50] With the exception of infrared wavelengths close to visible light, such radiation is heavily absorbed by the atmosphere, or masked, as the atmosphere itself produces significant infrared emission. Consequently, infrared observatories have to be located in high, dry places on Earth or in space.[51] Some molecules radiate strongly in the infrared. This allows the study of the chemistry of space; more specifically it can detect water in comets.[52] Optical astronomy The Subaru Telescope (left) and Keck Observatory (center) on Mauna Kea, both examples of an observatory that operates at near-infrared and visible wavelengths. The NASA Infrared Telescope Facility (right) is an example of a telescope that operates only at near-infrared wavelengths. Main article: Optical astronomy Historically, optical astronomy, also called visible light astronomy, is the oldest form of astronomy.[53] Images of observations were originally drawn by hand. In the late 19th century and most of the 20th century, images were made using photographic equipment. Modern images are made using digital detectors, particularly using charge-coupled devices (CCDs) and recorded on modern medium. Although visible light itself extends from approximately 4000 Å to 7000 Å (400 nm to 700 nm),[53] that same equipment can be used to observe some near-ultraviolet and near-infrared radiation. Ultraviolet astronomy Main article: Ultraviolet astronomy Ultraviolet astronomy employs ultraviolet wavelengths between approximately 100 and 3200 Å (10 to 320 nm).[47] Light at those wavelengths is absorbed by the Earth's atmosphere, requiring observations at these wavelengths to be performed from the upper atmosphere or from space. Ultraviolet astronomy is best suited to the study of thermal radiation and spectral emission lines from hot blue stars (OB stars) that are very bright in this wave band. This includes the blue stars in other galaxies, which have been the targets of several ultraviolet surveys. Other objects commonly observed in ultraviolet light include planetary nebulae, supernova remnants, and active galactic nuclei.[47] However, as ultraviolet light is easily absorbed by interstellar dust, an adjustment of ultraviolet measurements is necessary.[47] X-ray astronomy Main article: X-ray astronomy X-ray jet made from a supermassive black hole found by NASA's Chandra X-ray Observatory, made visible by light from the early Universe X-ray astronomy uses X-ray wavelengths. Typically, X-ray radiation is produced by synchrotron emission (the result of electrons orbiting magnetic field lines), thermal emission from thin gases above 107 (10 million) kelvins, and thermal emission from thick gases above 107 Kelvin.[47] Since X-rays are absorbed by the Earth's atmosphere, all X-ray observations must be performed from high-altitude balloons, rockets, or X-ray astronomy satellites. Notable X-ray sources include X-ray binaries, pulsars, supernova remnants, elliptical galaxies, clusters of galaxies, and active galactic nuclei.[47] Gamma-ray astronomy Main article: Gamma ray astronomy Gamma ray astronomy observes astronomical objects at the shortest wavelengths of the electromagnetic spectrum. Gamma rays may be observed directly by satellites such as the Compton Gamma Ray Observatory or by specialized telescopes called atmospheric Cherenkov telescopes.[47] The Cherenkov telescopes do not detect the gamma rays directly but instead detect the flashes of visible light produced when gamma rays are absorbed by the Earth's atmosphere.[54] Most gamma-ray emitting sources are actually gamma-ray bursts, objects which only produce gamma radiation for a few milliseconds to thousands of seconds before fading away. Only 10% of gamma-ray sources are non-transient sources. These steady gamma-ray emitters include pulsars, neutron stars, and black hole candidates such as active galactic nuclei.[47] Fields not based on the electromagnetic spectrum In addition to electromagnetic radiation, a few other events originating from great distances may be observed from the Earth. In neutrino astronomy, astronomers use heavily shielded underground facilities such as SAGE, GALLEX, and Kamioka II/III for the detection of neutrinos. The vast majority of the neutrinos streaming through the Earth originate from the Sun, but 24 neutrinos were also detected from supernova 1987A.[47] Cosmic rays, which consist of very high energy particles (atomic nuclei) that can decay or be absorbed when they enter the Earth's atmosphere, result in a cascade of secondary particles which can be detected by current observatories.[55] Some future neutrino detectors may also be sensitive to the particles produced when cosmic rays hit the Earth's atmosphere.[47] Gravitational-wave astronomy is an emerging field of astronomy that employs gravitational-wave detectors to collect observational data about distant massive objects. A few observatories have been constructed, such as the Laser Interferometer Gravitational Observatory LIGO. LIGO made its first detection on 14 September 2015, observing gravitational waves from a binary black hole.[56] A second gravitational wave was detected on 26 December 2015 and additional observations should continue but gravitational waves require extremely sensitive instruments.[57][58] The combination of observations made using electromagnetic radiation, neutrinos or gravitational waves and other complementary information, is known as multi-messenger astronomy.[59][60] Astrometry and celestial mechanics Main articles: Astrometry and Celestial mechanics Star cluster Pismis 24 with a nebula One of the oldest fields in astronomy, and in all of science, is the measurement of the positions of celestial objects. Historically, accurate knowledge of the positions of the Sun, Moon, planets and stars has been essential in celestial navigation (the use of celestial objects to guide navigation) and in the making of calendars.[61]: 39  Careful measurement of the positions of the planets has led to a solid understanding of gravitational perturbations, and an ability to determine past and future positions of the planets with great accuracy, a field known as celestial mechanics. More recently the tracking of near-Earth objects will allow for predictions of close encounters or potential collisions of the Earth with those objects.[62] The measurement of stellar parallax of nearby stars provides a fundamental baseline in the cosmic distance ladder that is used to measure the scale of the Universe. Parallax measurements of nearby stars provide an absolute baseline for the properties of more distant stars, as their properties can be compared. Measurements of the radial velocity and proper motion of stars allow astronomers to plot the movement of these systems through the Milky Way galaxy. Astrometric results are the basis used to calculate the distribution of speculated dark matter in the galaxy.[63] During the 1990s, the measurement of the stellar wobble of nearby stars was used to detect large extrasolar planets orbiting those stars.[64] Theoretical astronomy Nucleosynthesis Stellar nucleosynthesis Big Bang nucleosynthesis Supernova nucleosynthesis Cosmic ray spallation Related topics Astrophysics Nuclear fusion R-process S-process Nuclear fission vte Main article: Theoretical astronomy Theoretical astronomers use several tools including analytical models and computational numerical simulations; each has its particular advantages. Analytical models of a process are better for giving broader insight into the heart of what is going on. Numerical models reveal the existence of phenomena and effects otherwise unobserved.[65][66] Theorists in astronomy endeavor to create theoretical models that are based on existing observations and known physics, and to predict observational consequences of those models. The observation of phenomena predicted by a model allows astronomers to select between several alternative or conflicting models. Theorists also modify existing models to take into account new observations. In some cases, a large amount of observational data that is inconsistent with a model may lead to abandoning it largely or completely, as for geocentric theory, the existence of luminiferous aether, and the steady-state model of cosmic evolution. Phenomena modeled by theoretical astronomers include: stellar dynamics and evolution galaxy formation large-scale distribution of matter in the Universe the origin of cosmic rays general relativity and physical cosmology, including string cosmology and astroparticle physics. Modern theoretical astronomy reflects dramatic advances in observation since the 1990s, including studies of the cosmic microwave background, distant supernovae and galaxy redshifts, which have led to the development of a standard model of cosmology. This model requires the universe to contain large amounts of dark matter and dark energy whose nature is currently not well understood, but the model gives detailed predictions that are in excellent agreement with many diverse observations.[67] Specific subfields Astrophysics Main article: Astrophysics Astrophysics applies physics and chemistry to understand the measurements made by astronomy. Representation of the Observable Universe that includes images from Hubble and other telescopes. Astrophysics is the branch of astronomy that employs the principles of physics and chemistry "to ascertain the nature of the astronomical objects, rather than their positions or motions in space".[68][69] Among the objects studied are the Sun, other stars, galaxies, extrasolar planets, the interstellar medium and the cosmic microwave background.[70][71] Their emissions are examined across all parts of the electromagnetic spectrum, and the properties examined include luminosity, density, temperature, and chemical composition. Because astrophysics is a very broad subject, astrophysicists typically apply many disciplines of physics, including mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics. In practice, modern astronomical research often involves a substantial amount of work in the realms of theoretical and observational physics. Some areas of study for astrophysicists include their attempts to determine the properties of dark matter, dark energy, and black holes; whether or not time travel is possible, wormholes can form, or the multiverse exists; and the origin and ultimate fate of the universe.[70] Topics also studied by theoretical astrophysicists include Solar System formation and evolution; stellar dynamics and evolution; galaxy formation and evolution; magnetohydrodynamics; large-scale structure of matter in the universe; origin of cosmic rays; general relativity and physical cosmology, including string cosmology and astroparticle physics. Astrochemistry Main article: Astrochemistry Astrochemistry is the study of the abundance and reactions of molecules in the Universe, and their interaction with radiation. The discipline is an overlap of astronomy and chemistry. The word "astrochemistry" may be applied to both the Solar System and the interstellar medium. The study of the abundance of elements and isotope ratios in Solar System objects, such as meteorites, is also called cosmochemistry, while the study of interstellar atoms and molecules and their interaction with radiation is sometimes called molecular astrophysics. The formation, atomic and chemical composition, evolution and fate of molecular gas clouds is of special interest, because it is from these clouds that solar systems form. Studies in this field contribute to the understanding of the formation of the Solar System, Earth's origin and geology, abiogenesis, and the origin of climate and oceans.[72] Astrobiology Main article: Astrobiology Astrobiology is an interdisciplinary scientific field concerned with the origins, early evolution, distribution, and future of life in the universe. Astrobiology considers the question of whether extraterrestrial life exists, and how humans can detect it if it does.[73] The term exobiology is similar.[74] Astrobiology makes use of molecular biology, biophysics, biochemistry, chemistry, astronomy, physical cosmology, exoplanetology and geology to investigate the possibility of life on other worlds and help recognize biospheres that might be different from that on Earth.[75] The origin and early evolution of life is an inseparable part of the discipline of astrobiology.[76] Astrobiology concerns itself with interpretation of existing scientific data, and although speculation is entertained to give context, astrobiology concerns itself primarily with hypotheses that fit firmly into existing scientific theories. This interdisciplinary field encompasses research on the origin of planetary systems, origins of organic compounds in space, rock-water-carbon interactions, abiogenesis on Earth, planetary habitability, research on biosignatures for life detection, and studies on the potential for life to adapt to challenges on Earth and in outer space.[77][78][79] Physical cosmology Nature timeline This box: viewtalkedit −13 —–−12 —–−11 —–−10 —–−9 —–−8 —–−7 —–−6 —–−5 —–−4 —–−3 —–−2 —–−1 —–0 — Dark Ages Reionization Matter-dominated era Accelerated expansion Water on Earth Single-celled life Photosynthesis Multicellular life Vertebrates ← Earliest Universe ← Earliest stars ← Earliest galaxy ← Earliest quasar / black hole ← Omega Centauri ← Andromeda Galaxy ← Milky Way spirals ← NGC 188 star cluster ← Alpha Centauri ← Earth / Solar System ← Earliest known life ← Earliest oxygen ← Atmospheric oxygen ← Sexual reproduction ← Earliest fungi ← Earliest animals / plants ← Cambrian explosion ← Earliest mammals ← Earliest apes / humans L i f e (billion years ago) Main article: Physical cosmology Cosmology (from the Greek κόσμος (kosmos) "world, universe" and λόγος (logos) "word, study" or literally "logic") could be considered the study of the Universe as a whole. Hubble Extreme Deep Field Observations of the large-scale structure of the Universe, a branch known as physical cosmology, have provided a deep understanding of the formation and evolution of the cosmos. Fundamental to modern cosmology is the well-accepted theory of the Big Bang, wherein our Universe began at a single point in time, and thereafter expanded over the course of 13.8 billion years[80] to its present condition.[81] The concept of the Big Bang can be traced back to the discovery of the microwave background radiation in 1965.[81] In the course of this expansion, the Universe underwent several evolutionary stages. In the very early moments, it is theorized that the Universe experienced a very rapid cosmic inflation, which homogenized the starting conditions. Thereafter, nucleosynthesis produced the elemental abundance of the early Universe.[81] (See also nucleocosmochronology.) When the first neutral atoms formed from a sea of primordial ions, space became transparent to radiation, releasing the energy viewed today as the microwave background radiation. The expanding Universe then underwent a Dark Age due to the lack of stellar energy sources.[82] A hierarchical structure of matter began to form from minute variations in the mass density of space. Matter accumulated in the densest regions, forming clouds of gas and the earliest stars, the Population III stars. These massive stars triggered the reionization process and are believed to have created many of the heavy elements in the early Universe, which, through nuclear decay, create lighter elements, allowing the cycle of nucleosynthesis to continue longer.[83] Gravitational aggregations clustered into filaments, leaving voids in the gaps. Gradually, organizations of gas and dust merged to form the first primitive galaxies. Over time, these pulled in more matter, and were often organized into groups and clusters of galaxies, then into larger-scale superclusters.[84] Fundamental to the structure of the Universe is the existence of dark matter and dark energy. These are now thought to be its dominant components, forming 96% of the mass of the Universe. For this reason, much effort is expended in trying to understand the physics of these components.[85] Extragalactic astronomy This image shows several blue, loop-shaped objects that are multiple images of the same galaxy, duplicated by the gravitational lens effect of the cluster of yellow galaxies near the middle of the photograph. The lens is produced by the cluster's gravitational field that bends light to magnify and distort the image of a more distant object. Main article: Extragalactic astronomy The study of objects outside our galaxy is a branch of astronomy concerned with the formation and evolution of galaxies, their morphology (description) and classification, the observation of active galaxies, and at a larger scale, the groups and clusters of galaxies. Finally, the latter is important for the understanding of the large-scale structure of the cosmos.[61] Most galaxies are organized into distinct shapes that allow for classification schemes. They are commonly divided into spiral, elliptical and Irregular galaxies.[86] As the name suggests, an elliptical galaxy has the cross-sectional shape of an ellipse. The stars move along random orbits with no preferred direction. These galaxies contain little or no interstellar dust, few star-forming regions, and older stars.[61]: 877–878  Elliptical galaxies may have been formed by other galaxies merging.[61]: 939  A spiral galaxy is organized into a flat, rotating disk, usually with a prominent bulge or bar at the center, and trailing bright arms that spiral outward. The arms are dusty regions of star formation within which massive young stars produce a blue tint. Spiral galaxies are typically surrounded by a halo of older stars. Both the Milky Way and one of our nearest galaxy neighbors, the Andromeda Galaxy, are spiral galaxies.[61]: 875  Irregular galaxies are chaotic in appearance, and are neither spiral nor elliptical.[61]: 879  About a quarter of all galaxies are irregular, and the peculiar shapes of such galaxies may be the result of gravitational interaction.[87] An active galaxy is a formation that emits a significant amount of its energy from a source other than its stars, dust and gas. It is powered by a compact region at the core, thought to be a supermassive black hole that is emitting radiation from in-falling material.[61]: 907  A radio galaxy is an active galaxy that is very luminous in the radio portion of the spectrum, and is emitting immense plumes or lobes of gas. Active galaxies that emit shorter frequency, high-energy radiation include Seyfert galaxies, quasars, and blazars. Quasars are believed to be the most consistently luminous objects in the known universe.[88] The large-scale structure of the cosmos is represented by groups and clusters of galaxies. This structure is organized into a hierarchy of groupings, with the largest being the superclusters. The collective matter is formed into filaments and walls, leaving large voids between.[89] Galactic astronomy Observed structure of the Milky Way's spiral arms Main article: Galactic astronomy The Solar System orbits within the Milky Way, a barred spiral galaxy that is a prominent member of the Local Group of galaxies. It is a rotating mass of gas, dust, stars and other objects, held together by mutual gravitational attraction. As the Earth is located within the dusty outer arms, there are large portions of the Milky Way that are obscured from view.[61]: 837–842, 944  In the center of the Milky Way is the core, a bar-shaped bulge with what is believed to be a supermassive black hole at its center. This is surrounded by four primary arms that spiral from the core. This is a region of active star formation that contains many younger, population I stars. The disk is surrounded by a spheroid halo of older, population II stars, as well as relatively dense concentrations of stars known as globular clusters.[90] Between the stars lies the interstellar medium, a region of sparse matter. In the densest regions, molecular clouds of molecular hydrogen and other elements create star-forming regions. These begin as a compact pre-stellar core or dark nebulae, which concentrate and collapse (in volumes determined by the Jeans length) to form compact protostars.[91] As the more massive stars appear, they transform the cloud into an H II region (ionized atomic hydrogen) of glowing gas and plasma. The stellar wind and supernova explosions from these stars eventually cause the cloud to disperse, often leaving behind one or more young open clusters of stars. These clusters gradually disperse, and the stars join the population of the Milky Way.[92] Kinematic studies of matter in the Milky Way and other galaxies have demonstrated that there is more mass than can be accounted for by visible matter. A dark matter halo appears to dominate the mass, although the nature of this dark matter remains undetermined.[93] Stellar astronomy Mz 3, often referred to as the Ant planetary nebula. Ejecting gas from the dying central star shows symmetrical patterns unlike the chaotic patterns of ordinary explosions. Main article: Star See also: Solar astronomy The study of stars and stellar evolution is fundamental to our understanding of the Universe. The astrophysics of stars has been determined through observation and theoretical understanding; and from computer simulations of the interior.[94] Star formation occurs in dense regions of dust and gas, known as giant molecular clouds. When destabilized, cloud fragments can collapse under the influence of gravity, to form a protostar. A sufficiently dense, and hot, core region will trigger nuclear fusion, thus creating a main-sequence star.[91] Almost all elements heavier than hydrogen and helium were created inside the cores of stars.[94] The characteristics of the resulting star depend primarily upon its starting mass. The more massive the star, the greater its luminosity, and the more rapidly it fuses its hydrogen fuel into helium in its core. Over time, this hydrogen fuel is completely converted into helium, and the star begins to evolve. The fusion of helium requires a higher core temperature. A star with a high enough core temperature will push its outer layers outward while increasing its core density. The resulting red giant formed by the expanding outer layers enjoys a brief life span, before the helium fuel in the core is in turn consumed. Very massive stars can also undergo a series of evolutionary phases, as they fuse increasingly heavier elements.[95] The final fate of the star depends on its mass, with stars of mass greater than about eight times the Sun becoming core collapse supernovae;[96] while smaller stars blow off their outer layers and leave behind the inert core in the form of a white dwarf. The ejection of the outer layers forms a planetary nebula.[97] The remnant of a supernova is a dense neutron star, or, if the stellar mass was at least three times that of the Sun, a black hole.[98] Closely orbiting binary stars can follow more complex evolutionary paths, such as mass transfer onto a white dwarf companion that can potentially cause a supernova.[99] Planetary nebulae and supernovae distribute the "metals" produced in the star by fusion to the interstellar medium; without them, all new stars (and their planetary systems) would be formed from hydrogen and helium alone.[100] Solar astronomy An ultraviolet image of the Sun's active photosphere as viewed by the TRACE space telescope. NASA photo Solar observatory Lomnický štít (Slovakia) built in 1962 Main article: Sun See also: Solar telescope At a distance of about eight light-minutes, the most frequently studied star is the Sun, a typical main-sequence dwarf star of stellar class G2 V, and about 4.6 billion years (Gyr) old. The Sun is not considered a variable star, but it does undergo periodic changes in activity known as the sunspot cycle. This is an 11-year oscillation in sunspot number. Sunspots are regions of lower-than- average temperatures that are associated with intense magnetic activity.[101] The Sun has steadily increased in luminosity by 40% since it first became a main-sequence star. The Sun has also undergone periodic changes in luminosity that can have a significant impact on the Earth.[102] The Maunder minimum, for example, is believed to have caused the Little Ice Age phenomenon during the Middle Ages.[103] At the center of the Sun is the core region, a volume of sufficient temperature and pressure for nuclear fusion to occur. Above the core is the radiation zone, where the plasma conveys the energy flux by means of radiation. Above that is the convection zone where the gas material transports energy primarily through physical displacement of the gas known as convection. It is believed that the movement of mass within the convection zone creates the magnetic activity that generates sunspots.[101] The visible outer surface of the Sun is called the photosphere. Above this layer is a thin region known as the chromosphere. This is surrounded by a transition region of rapidly increasing temperatures, and finally by the super-heated corona.[61]: 498–502  A solar wind of plasma particles constantly streams outward from the Sun until, at the outermost limit of the Solar System, it reaches the heliopause. As the solar wind passes the Earth, it interacts with the Earth's magnetic field (magnetosphere) and deflects the solar wind, but traps some creating the Van Allen radiation belts that envelop the Earth. The aurora are created when solar wind particles are guided by the magnetic flux lines into the Earth's polar regions where the lines then descend into the atmosphere.[104] Planetary science The black spot at the top is a dust devil climbing a crater wall on Mars. This moving, swirling column of Martian atmosphere (comparable to a terrestrial tornado) created the long, dark streak. Main articles: Planetary science and Planetary geology Planetary science is the study of the assemblage of planets, moons, dwarf planets, comets, asteroids, and other bodies orbiting the Sun, as well as extrasolar planets. The Solar System has been relatively well-studied, initially through telescopes and then later by spacecraft. This has provided a good overall understanding of the formation and evolution of the Sun's planetary system, although many new discoveries are still being made.[105] The Solar System is divided into the inner Solar System (subdivided into the inner planets and the asteroid belt), the outer Solar System (subdivided into the outer planets and centaurs), comets, the trans-Neptunian region (subdivided into the Kuiper belt, and the scattered disc) and the farthest regions (e.g., boundaries of the heliosphere, and the Oort Cloud, which may extend as far as a light-year). The inner terrestrial planets consist of Mercury, Venus, Earth, and Mars. The outer giant planets are the gas giants (Jupiter and Saturn) and the ice giants (Uranus and Neptune).[106] The planets were formed 4.6 billion years ago in the protoplanetary disk that surrounded the early Sun. Through a process that included gravitational attraction, collision, and accretion, the disk formed clumps of matter that, with time, became protoplanets. The radiation pressure of the solar wind then expelled most of the unaccreted matter, and only those planets with sufficient mass retained their gaseous atmosphere. The planets continued to sweep up, or eject, the remaining matter during a period of intense bombardment, evidenced by the many impact craters on the Moon. During this period, some of the protoplanets may have collided and one such collision may have formed the Moon.[107] Once a planet reaches sufficient mass, the materials of different densities segregate within, during planetary differentiation. This process can form a stony or metallic core, surrounded by a mantle and an outer crust. The core may include solid and liquid regions, and some planetary cores generate their own magnetic field, which can protect their atmospheres from solar wind stripping.[108] A planet or moon's interior heat is produced from the collisions that created the body, by the decay of radioactive materials (e.g. uranium, thorium, and 26Al), or tidal heating caused by interactions with other bodies. Some planets and moons accumulate enough heat to drive geologic processes such as volcanism and tectonics. Those that accumulate or retain an atmosphere can also undergo surface erosion from wind or water. Smaller bodies, without tidal heating, cool more quickly; and their geological activity ceases with the exception of impact cratering.[109] Interdisciplinary studies Astronomy and astrophysics have developed significant interdisciplinary links with other major scientific fields. Archaeoastronomy is the study of ancient or traditional astronomies in their cultural context, utilizing archaeological and anthropological evidence. Astrobiology is the study of the advent and evolution of biological systems in the Universe, with particular emphasis on the possibility of non-terrestrial life. Astrostatistics is the application of statistics to astrophysics to the analysis of a vast amount of observational astrophysical data.[110] The study of chemicals found in space, including their formation, interaction and destruction, is called astrochemistry. These substances are usually found in molecular clouds, although they may also appear in low-temperature stars, brown dwarfs and planets. Cosmochemistry is the study of the chemicals found within the Solar System, including the origins of the elements and variations in the isotope ratios. Both of these fields represent an overlap of the disciplines of astronomy and chemistry. As "forensic astronomy", finally, methods from astronomy have been used to solve problems of art history[111][112] and occasionally of law.[113] Amateur astronomy Amateur astronomers can build their own equipment, and hold star parties and gatherings, such as Stellafane. Main article: Amateur astronomy Astronomy is one of the sciences to which amateurs can contribute the most.[114] Collectively, amateur astronomers observe a variety of celestial objects and phenomena sometimes with consumer-level equipment or equipment that they build themselves. Common targets of amateur astronomers include the Sun, the Moon, planets, stars, comets, meteor showers, and a variety of deep-sky objects such as star clusters, galaxies, and nebulae. Astronomy clubs are located throughout the world and many have programs to help their members set up and complete observational programs including those to observe all the objects in the Messier (110 objects) or Herschel 400 catalogues of points of interest in the night sky. One branch of amateur astronomy, astrophotography, involves the taking of photos of the night sky. Many amateurs like to specialize in the observation of particular objects, types of objects, or types of events that interest them.[115][116] Most amateurs work at visible wavelengths, but many experiment with wavelengths outside the visible spectrum. This includes the use of infrared filters on conventional telescopes, and also the use of radio telescopes. The pioneer of amateur radio astronomy was Karl Jansky, who started observing the sky at radio wavelengths in the 1930s. A number of amateur astronomers use either homemade telescopes or use radio telescopes which were originally built for astronomy research but which are now available to amateurs (e.g. the One-Mile Telescope).[117][118] Amateur astronomers continue to make scientific contributions to the field of astronomy and it is one of the few scientific disciplines where amateurs can still make significant contributions. Amateurs can make occultation measurements that are used to refine the orbits of minor planets. They can also discover comets, and perform regular observations of variable stars. Improvements in digital technology have allowed amateurs to make impressive advances in the field of astrophotography.[119][120][121] Unsolved problems in astronomy Main article: List of unsolved problems in astronomy In the 21st century there remain important unanswered questions in astronomy. Some are cosmic in scope: for example, what are dark matter and dark energy? These dominate the evolution and fate of the cosmos, yet their true nature remains unknown.[122] What will be the ultimate fate of the universe?[123] Why is the abundance of lithium in the cosmos four times lower than predicted by the standard Big Bang model?[124] Others pertain to more specific classes of phenomena. For example, is the Solar System normal or atypical?[125] What is the origin of the stellar mass spectrum? That is, why do astronomers observe the same distribution of stellar masses—the initial mass function—apparently regardless of the initial conditions?[126] Likewise, questions remain about the formation of the first galaxies,[127] the origin of supermassive black holes,[128] the source of ultra-high-energy cosmic rays,[129] and more. Is there other life in the Universe? Especially, is there other intelligent life? If so, what is the explanation for the Fermi paradox? 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