3 min read · Sky
A full moon rising over the horizon often looks orange and enormous, then turns white and smaller as it climbs. The Moon itself does not change. Our atmosphere changes its color, and our brain changes its size.
Why a low Moon looks orange
When the Moon is near the horizon, its light travels through much more air to reach you than when it is overhead. Air scatters blue light more than red light (the same effect that makes the daytime sky blue), so by the time moonlight reaches you, more of the blue has been removed and it looks yellow, orange, or even red. Smoke, dust, and haze make the effect stronger.
Why a blood moon is red
During a total lunar eclipse, Earth blocks direct sunlight from the Moon. Some sunlight still bends through Earth’s atmosphere and reaches it, and that light has passed through the equivalent of every sunrise and sunset on Earth at once, so it is red. How dark or bright red it looks depends on how much dust and cloud is in our atmosphere at the time.
The moon illusion
The Moon looks bigger near the horizon, but it is not. Measured with a camera, it is the same size, and technically very slightly smaller, because it is a little farther from you than when it is overhead. The effect is in how your brain judges size next to trees and buildings, and scientists still debate exactly why it happens.
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