Have you ever heard someone claim that the Moon is made of cheese? It probably seemed like a funny notion. If you've seen the Moon in different colors, though, you might start to believe there's some truth to this whole "made of cheese" thing.
For example, sometimes the Moon appears white, while at other times it's more yellow or even orange. If it was made of cheese, you could explain these different colors by types of cheese: mozzarella for white, American for yellow, and cheddar for orange!
Rest assured. The Moon is NOT made of cheese. Then how do you explain the different colors of the Moon? Why does it appear different colors at different times? Is the Man in the Moon changing the light bulb between phases?
If you've ever seen a huge harvest Moon in the fall, hanging low on the horizon and glowing a brilliant orange, you may have WONDERed what causes that orange glow that can make the moon look almost like the Sun.
Although it seems to change colors, the Moon itself stays the same color year-round. The different colors we see from time to time are the result of our particular viewing angle, along with the composition of Earth's atmosphere.
It takes about a month for the Moon to travel all the way around Earth. At the same time the Moon is moving around Earth, Earth is spinning on its axis and both Earth and the Moon are traveling around the Sun. All this celestial movement accounts for the fact that the Moon takes different paths through the sky each night.
You may have noticed that you're most likely to see a brilliant orange Moon when it's hanging low in the sky, close to the horizon. That's because you're seeing the Moon through much more of Earth's atmosphere than when you see it high in the sky.
Earth's atmosphere is like a sphere of gases that surround the planet. When you look straight up into the night sky at the Moon, you're looking through a thin band of atmosphere that only extends a tiny fraction of the distance to the Moon.
When the Moon hangs low in the sky near the horizon, though, you're seeing it through a much thicker layer of Earth's atmosphere. Why does this matter? Earth's atmosphere is filled with all sorts of airborne particles that absorb and scatter light.
These atmospheric particles tend to scatter shorter wavelengths of light more than longer wavelengths. Orange and red light, which have longer wavelengths, tend to pass through the atmosphere, while shorter wavelengths of light, such as blue, get scattered.
That's why the Moon — and the Sun! — look orange or red when they're rising or setting. At those times, they're low in the sky close to the horizon and their light must travel through the maximum amount of atmosphere to reach your eyes.
But what about those times when you've seen an orange Moon higher in the sky? If you've ever seen an orange Moon high in the sky, the atmosphere is still the reason it's orange. In certain areas, the atmosphere can be filled with air pollution, dust, and even smoke from wildfires. These particles scatter light in the same way described above, leading to an orange or red Moon high in the sky.