Moon's Glow

A blood moon against the night sky in 2014. Credit: NASA Ames Research Center/Brian Day

When you look up at the night sky, some nights we’ll see a full moon glowing in the midst of all the blackness that surrounds it. Some nights, the moon appears golden; other nights, it has a silvery glow. 

So, how does the moon change color? Well, it doesn’t. The moon itself doesn’t make its own light so the colors you see vary based on how the sunlight reflects on the moon’s surface. This is why moonlight is much more gentle and subdued than direct sunlight.

The moon’s surface is covered in dust and rock terrain, made up of ancient volcanic rock, much like what you see at volcanic sites here on Earth. And these dark rocks absorb much of the light from the sun. Only about a tenth of the sunlight that hits the moon’s surface actually gets reflected back into space. As a comparison, Earth, with our vast oceans, reflects back three-tenths of the sunlight back into space. 

As the moon rotates and orbits around the Earth, the angle the sunlight hits the moon’s surface changes causing the different hues. The moon’s position in relation to the Sun and Earth affects how we see the moon. 

The “blood moon”, for example, which we see during a total lunar eclipse, appears red. During a total lunar eclipse, Earth lines up between the Moon and the Sun, which prevents sunlight from reflecting off the Moon. So, the only light, then, that reaches the Moon is from the Earth’s atmosphere. The Earth’s atmosphere scatters the blue light, which results in the Moon having a red glow. 

Tonight when you go out and see the moon, you’ll know that what gives your skin a natural glow is also responsible for the moon’s glow too.