Say, you know how the moon looks really big when it's near the horizon, but then all small and pathetic when it's up overhead?
This is what's cleverly called the "moon illusion," and it's actually an optical illusion, not anything caused by the atmosphere or like that. You can prove this by taking a picture of the phenomenon. The moon will look regular sized in the photograph, and you'll be telling your friends, "Really, it was so super huge when I took the picture, it was really beautiful." And they'll be all, "Yeah, right, moony. Way to take a crap picture of the moon." The picture above, for example, is a composite. You couldn't take that picture. (But if it's any consolation, neither could your jerk friends.)
You can also hold a ruler up to the image of the moon and measure it's size, then do the same thing when it's overhead. Same size. It's all in your mind.
I, for one, find this cool.
So it interests me that the full moon this week hangs lower in the sky than any moon since 1987, which will cause the illusion to be extra strong.
What's even more interesting is that despite thousands of years of documentation of this illusion, no one really knows exactly why it happens. Some have claimed that it is because of the relative size of earthly things tricking your brain into seeing the moon as comparatively large, as opposed to when it's overhead, surrounded by a whole lot of nothing.
Pilots, though, have noted the effect when flying thousands of feet up, with no particular human-scale references on the horizon. Also, if this were the case, why wouldn't the moon look bigger on a cloudy night? I don't buy it.
Other, more sciencey explanations are around, but they're too long and contain words like oculomotor micropsia, so forget that.
The full moon is this Wednesday, the day after the summer solstice. To find out what time it will rise in your town, consult this widget.
So go out this evening or next and check it out. I'm going to try to see it tonight, as it's an extra clear day in Seattle.
