Why Does The Moon Glow?
QUICK ANSWER
The Moon doesn't actually glow. It reflects sunlight from its surface, which is why it appears bright in our night sky. The Moon's surface is roughly as reflective as old asphalt (reflecting about 12% of incoming sunlight), but against the black night sky, even that small amount of reflected light looks brilliant.
The Moon doesn't make its own light. Everything you see when you look at the Moon is reflected sunlight bouncing off the lunar surface. The surface itself is actually pretty dark, similar to worn asphalt, but against the black sky it still looks brilliantly bright.
Does the Moon actually glow?
No. According to NASA, the Moon doesn't generate its own light. The Moon is a rocky body without an atmosphere or any source of energy that could produce visible light on its own. What we see when we look at the Moon is sunlight that has bounced off the lunar surface and traveled to our eyes on Earth. The same is true for the planets, which also appear bright in our sky because they reflect sunlight. Only stars (and a few exotic objects like nebulae) actually produce their own light.
How reflective is the Moon's surface?
Surprisingly dim, at about 12 percent reflectivity. The technical term is albedo, and the Moon's albedo is about 0.12, similar to old asphalt or worn coal. The lunar surface looks bright to us only because we see it against the much darker background of space. If you saw the Moon next to a white sheet of paper in good lighting, the paper would look much brighter. The dark coloration comes from the iron-rich basaltic rocks that cover much of the surface, particularly the dark areas known as maria (Latin for seas).
Why does the Moon look so bright then?
Contrast against the dark sky. Even though the Moon's surface only reflects about 12 percent of incoming sunlight, the sky around it is essentially black, so even a small amount of reflected light stands out brilliantly. The full moon is bright enough to cast distinct shadows on Earth's surface and to read by under clear skies. The brightness depends on the phase: full moon is about 12 times brighter than first or third quarter, because we see far more of the lit side.
Why does the Moon look different colors?
Atmospheric effects, mostly. When the Moon is near the horizon, sunlight reflecting off the Moon has to travel through more of Earth's atmosphere to reach us. The atmosphere scatters away the blue wavelengths, leaving the reds and oranges to come through. That's why the Moon often looks reddish or orange when it's rising or setting. When the Moon is high in the sky, the light passes through less atmosphere and reaches us closer to its natural color, a pale gray-white. The Moon itself doesn't change color; the atmosphere does the filtering.
The Moon doesn't actually glow. It reflects sunlight from its dark gray surface, which appears bright only because the night sky behind it is darker. The Moon is about as reflective as old asphalt but bright enough against the dark sky to cast shadows on Earth. The color shifts we sometimes see (red moon at the horizon, white moon overhead) are caused by Earth's atmosphere, not the Moon itself.
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