Have you ever walked into a room and immediately forgotten the reason you're there? A solid thought convinced your legs to move, but by the time you reach your destination, you realise the thought has abandoned you en route. No, it's not dementia. It's the doorway.

Impress your friends (and potential dates) by being able to answer such questions as:

- Why the sky is blue?

- Why is it dark at night?

- Why does lunacy erupt under a full moon?

- What's the truth about Spinach and Popeye?

Dr Karl Kruszelnicki is the Julius Sumner Miller Fellow at the University of Sydney. He is a qualified medical doctor, engineer, physicist and mathematician. This MasterGeek consistently appears on the list of the Top 15 Most Trusted Australians, and was this year named one of Australia's National Living Treasures..