When browsing photos of the Moon you might be surprised to find pictures in a variety of stunning colors, including red, yellow, orange, blue, and gray. Below, we’ve shared the science behind these colorful phenomena, which help to light up the Moon and fuel our imaginations.
Red Moon
The Moon depends on the Sun for natural light, which reflects on the lunar surface, so the Sun’s position can have a drastic effect on the Moon’s color. Every time there’s a total lunar eclipse – when the Earth is located between the Sun and Moon, preventing sunlight from hitting the lunar surface – the Moon takes on a reddish hue instead of going fully dark.
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Also known as a Blood Moon, the red coloration is due to Rayleigh scattering – the same phenomenon that causes the sky to turn red and orange during a sunset. During the eclipse, the Earth’s atmospheric content (i.e. dust, moisture, and cloud levels) also has a significant effect on the Moon’s hue. Mark your calendars – the next total lunar eclipse will occur on January 31, 2018.
Blue Moon
We all know the phrase “once in a blue moon,” but how often does the Moon actually look blue? In fact, the phenomenon is as rare as the cliche suggests, and blue-colored moons only occur every three years or so. Unlike the Blood Moon, blue moons can take place during any lunar phase, and they owe their coloration to increased smoke or dust particles in the atmosphere. These particles need to be 0.7 micron or larger, so they cause the natural light to scatter and change the Moon’s tint. Often, a blue moon will happen because of a volcanic eruption or a large forest fire.
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Yellow/Orange Moon
It takes about a month for the Moon to complete a full orbit around the Earth, and at the same time, both the Earth and Moon are orbiting around the Sun. This positioning plays a huge role in the Moon’s size and color. When the Moon looms large over the horizon it’s closer to the Earth’s surface, and this may give it a yellow or orange hue. When it’s closer to the Earth’s surface it has to travel through more atmospheric particles, like dust and pollution. These particles tend to scatter shorter wavelengths of light (like blue), leaving behind the longer wavelengths (like yellow and orange).
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Perhaps the best time to see this phenomenon is during the Harvest Moon, which is the full moon near the start of fall. During this time the Moon is much closer to the horizon, so it will take on a yellow or orange hue, depending on the size and quantity of particles in the air.
Gray Moon
When large atmospheric particles and eclipses aren’t changing the Moon’s color it tends to look gray, with light and dark gray sections distinguishable from each other. The near side of the Moon is primarily dark gray, and these areas indicate the most volcanic activity. Here, lava covered up most of the impact craters when it solidified. These former lava beds are called maria. For those that always thought the “Dark Side of the Moon” referred to the side not facing Earth, we’re here to tell you that the Near Side is always dark.
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The Moon tends to look yellow or white to the naked eye, so why does it look gray in so many photographs? Taken from space, these photos represent the Moon’s color more accurately than anything we capture from Earth. The lunar surface is largely composed of silicon, iron, oxygen, magnesium, and a few other elements, which produce that rocky gray color. Without Earth’s atmosphere getting in the way, we can capture these colors as they truly look on the surface.
