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Why is the moon another color tonight?

The moon has fascinated humanity since the beginning of time. This astronomical body appears different in the sky each night, going through various phases and sometimes even changing color. The moon’s appearance is tied to its position relative to the Earth and sun. On some nights, it can take on unusual or surprising colors like red, orange, yellow, or even blue. These odd moon colors have scientific explanations illuminating the various factors that can alter how the moon looks to observers on Earth.

The Basics of Lunar Phases and Orbit

First, to understand the moon’s changing appearance, one must consider some astronomical basics. The moon orbits the Earth in an elliptical orbit, taking about 27.3 days to complete one revolution. Meanwhile, the Earth is of course orbiting the sun. Where the moon lies in its orbit in relation to the Earth and sun determines what phase it appears to be from Earth. For example, a new moon occurs when the moon is between the Earth and sun. At this point, the side of the moon facing Earth would be completely darkened, rendering it nearly invisible in the sky.

Lunar Phase How Moon Appears Moon’s Position
New Moon Not visible Between Earth and Sun
Waxing Crescent Thin crescent Moving ahead of Earth
First Quarter Half lit up 90 degrees ahead of Earth
Waxing Gibbous More than half lit Continuing ahead of Earth
Full Moon Fully illuminated Opposite Earth from Sun
Waning Gibbous Less than half lit Moving behind Earth
Third Quarter Half lit up 90 degrees behind Earth
Waning Crescent Thin crescent Continuing behind Earth

As the moon moves around its orbit, different amounts of its surface get illuminated by the sun from Earth’s perspective. This creates the familiar lunar phases ranging from new moon to full moon and back again in a 29.5 day cycle. Now let’s look at how the moon can take on unusual colors at times when it should otherwise appear white or grayish.

Rayleigh Scattering

One mechanism that can give the moon different colors is called Rayleigh scattering. This is the same phenomenon that makes the sky appear blue during the day. Rayleigh scattering occurs when sunlight passes through the atmosphere and the gases scatter more blue light than red light. At night, the moon’s brightness can also induce Rayleigh scattering, giving it a blue or violet hue at times.

When might this happen? Well, the moon can take on more dramatic coloration when it is lower on the horizon and its light has to pass through more atmosphere. Moonrises and moonsets often accentuate the blue color. Smaller dust particles in the atmosphere from events like volcanic eruptions or forest fires can also contribute to more vivid red and orange hues by enhancing the scattering effects.

Lunar Eclipse Colors

Another circumstance when the moon can display unusual colors is during a lunar eclipse. A lunar eclipse happens when the Earth passes directly between the sun and moon, casting its shadow on the lunar surface. The moon doesn’t go completely dark, however, but rather takes on a reddish, orange, or brown color. This occurs due to the physics of Earth’s atmosphere.

The gases and particles that make up our atmosphere tend to scatter blue wavelengths of light. What gets left over and refracted onto the moon’s surface during an eclipse is more of the longer red and orange wavelengths. This gives the eclipsed moon a foreboding blood-red appearance, which has frightened people throughout history before the science was understood.

Moon Illusion

Have you ever noticed the moon looking unusually large near the horizon? This common “moon illusion” can also lend itself to color changing effects. When the moon is low on the horizon, our brains are tricked due to the lack of reference points into thinking it is larger than when overhead. This illusion also accentuates the reddish-orange color caused by the scattering of light through greater quantities of dusty atmosphere near the horizon.

So in summary, the moon can appear yellow, orange, red or blue in the right conditions based on the physics of light interacting with Earth’s atmosphere. Air molecules and particles scatter and filter the moon’s white light to give it more dramatic hues. The next time you see a red moon rising or an eerie eclipse, you’ll know the science behind the spectacle!

When a Blue Moon Isn’t Blue

You may have heard the expression “once in a blue moon” used to describe rare events. But while the moon can appear blue or bluish under the right conditions, a blue moon has nothing to do with the moon’s actual color.

In modern usage, a blue moon refers to the second full moon occurring in a calendar month. This happens about every 2-3 years because of the moon’s phases aligning with our calendar months. So sadly, a blue moon doesn’t refer to seeing the moon with a bluish teint caused by Rayleigh scattering. That attractiveevent is not tied to any calendar schedule but rather the presence of just the right atmospheric conditions.

Myths and Folklore Surrounding Moon Colors

The moon’s sometimes eerie appearance has spawned many myths and folktales over the millennia. Here are some examples of how various cultures have explained unusual moon colors:

  • Blood Moon – Many cultures associated a red or “blood” moon with violence, war, or catastrophe. This is linked to lunar eclipses where the moon becomes entirely reddened by Earth’s shadow.
  • Blue Moon – Rare blue moons were considered auspicious events by some Native American tribes, tied to the ripening of crops.
  • Black Moon – Some call the second new moon in a month a “black moon.” Folklore links these to famine or disease.
  • Strawberry Moon – June’s full moon is called the Strawberry Moon to mark the fruit’s harvest season.
  • Harvest Moon – The fall full moon nearest the autumn equinox has the name Harvest Moon across many cultures.

While these color names and traditions lack scientific basis, they show how humanity has always noticed and tried to explain the moon’s changing appearance. Modern astronomy provides the real physical reasons for these variations.


In the end, the reason the moon can take on various colors comes down to the effects of Earth’s atmosphere on the sunlight illuminating it. While many myths abound about differently colored moons, Rayleigh scattering and refraction can stretch the moon’s palette beyond its usual white and gray. The next time you see a red, orange, yellow or even blue moon in the sky, take a moment to appreciate the optical wonder and think on how humanity has always found magic in the mundane motions of the heavens.