Do-it-yourself: Proving the moon illusion is really an illusion.
The best time to see a supermoon is just after sunset. Something called the “moon illusion” makes the moon appear even bigger: The closer it is to the horizon, the larger it looks. No one knows exactly why this happens, but it is probably has something to do with our eyes. NASA has this handy hack so you yourself can prove it’s just an illusion. December 3rd’s Full Cold Moon will be the only supermoon of 2017.It should shine 16 percent brighter and 7 percent larger than normal.