Why is a full moon, yellower and bigger when it is coming up than when it is higher in the sky?  That's a good question about something that we all can see. Let's talk about the moon's color first. We see the moon only because of the sunlight that falls on it and is reflected. Actually, the moon is not a very good reflector, because its surface is all rocks and dirt. We see it in almost its true color when it is high in the sky. When the moon first comes up, its light reaches our eyes after an extra-long path through the atmosphere (大气). There are lots of particles (微粒) scattering (分散) light in that long path. Blue light is scattered more than other colors, which means that it doesn't reach your eyes. The light that is left over looks yellow to your eye. Now about the other question—why the moon seems to change in size. That's more complicated. It's not an effect of the atmosphere, the way color is; it's not caused by something fooling your eyes. It seems, instead, to be caused by something that fools your brain—an illusion(错觉). Here's a drawing that creates an illusion. The two cones(圆锥体) are really the same size. But the rest of the drawing makes the right-hand cone seem farther away. Your brain knows that faraway objects are really larger than they look. It decides that the right-hand cone must be larger because it seems to be farther away. Similarly, when you see the moon just come up over a line of trees or houses—or whatever makes the horizon(地平线)—it may be that your brain decides that the moon must be larger because it seems to be farther away. 小题1:The moon doesn't reflect the sunlight very well because________________.
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