You’re out for a walk, enjoying the last bit of a summer’s night breeze. When, to your surprise, you examine that the moon, a once gray-scaled rock, has now suddenly turned a deep Mars-like red. What has happened to the Moon?
Rest assured that the surface of the moon does not change in hue. But rather, the viewing angle and composition of the Earth’s atmosphere creates a filter in front of the Moon, which can change how the Moon looks from Earth.
When the Moon appears to change colors, several environmental conditions can cause ‘Moon filters’. Lunar eclipses, Harvest Moons, and pollution caused by wildfires are a few common annual occurrences that cause the once white and gray Moon to appear in bright reds, dull yellows, and striking oranges.
Credit: NASA
According to Robert Britt writer at Space.com, a lunar eclipse occurs when “the Earths shadow blocks the sun’s light, which otherwise reflects off the moon”. During a total eclipse, the Moon can take on dark intense muddy red. This is caused when some light from the sun passes through the Earth’s atmosphere and is then bent toward the moon.
Think of the Earth’s atmosphere as a sphere of gases that covers the planet. When the Moon is high in the night’s sky, it is viewed through a thinner layer of atmospheric gases. However, when the Moon hangs low closer to the horizon, it is viewed through a thicker layer of gases.
This is ultimately due to small airborne particles in the atmosphere that absorb and scatter light. When the Moon hangs low in the sky, it appears reddish in color because the Moon is being viewed at a lower angle through thicker levels of gases. The atmospheric particles scatter blues and cool colors near the horizon causing us to see reds.
There are times when the Moon is high and still has a reddish color. This is a result of pollution, dust, or smoke/ash from wildfires. These excess particles create a thicker atmosphere and when light travels through these areas, causing the Moon to appear red anywhere in the sky.
So the next time you hear someone say “the moon is so red!”, you can confidently say “this is not a red moon“.
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