Moon-Mars redness comparison.

Blood Red Moon: Total Lunar Eclipse

Why does the Moon look orange or red like Mars during a total lunar eclipse?

Mars has a reddish color because of the iron oxides (rust) on its surface. However, the reason the Moon looks red during a total lunar eclipse is quite different.

To understand why, let's understand what a lunar eclipse is all about. For any lunar eclipse, we need a full moon.

During a total lunar eclipse, the Sun, Earth, and Earth's moon line up in space.

The Sun shines on Earth, creating a shadow (umbra) that is just large enough to cover the Moon. Some indirect sunlight still gets to the Moon, however, because it is bent by our atmosphere, creating two areas of partial shadow, partial illumination (penumbra).

In its orbit around Earth, the full Moon gradually darkens bit by bit as it enters and travels through Earth's partial shadow. When the Moon is fully in the shadow of Earth (its umbra), the eclipse is total. At this time, something special happens!

The Moon turns golden, copper, or even "blood red"!

Why does the Moon turn red - sort of like Mars?

You'd think that because Earth's shadow is large enough to cover the moon during a total lunar eclipse, the Moon would go completely dark.

However, because Earth's atmosphere extends out beyond Earth, sunlight passes through it.

As mentioned, some of this light is bent back and projects onto the moon. But, why is this bent light gold, orange, or red in color?

Sunlight is an energy that travels in waves. A wavelength is the distance between the tops of the waves. Sunlight has a range of wavelengths, some of which are visible colors. Each color has a different wavelength. Violet has the shortest wavelength and red has the longest. When all of the waves are together, such as when they travel in space, the light is white. When white light passes through an atmosphere, it can be broken up into visible colors and other wavelengths.

During a total lunar eclipse, white sunlight hitting the atmosphere on the sides of the Earth gets absorbed and then radiated out (scattered). Blue-colored light is most affected. That is, the atmosphere filters out (scatters away) most of the blue-colored light. What's left over is the orange- and red-colored light. This red-colored light passes through our atmosphere without getting absorbed and scattered, before the atmosphere bends it (refracts it) back out, projecting indirect, reddish light onto the Moon. The reddish light projected on the Moon is much dimmer than the full white sunlight the Moon typically reflects back to us. That's because the light is indirect and because the red-colored wavelengths are only a part of what makes up the white light from the sun that the Moon usually receives.

How gold, orange, or red the Moon appears during a total lunar eclipse depends on how much dust, water, and other particles are in Earth's atmosphere, as well as factors such as temperature and humidity.

Red Ring Around the Earth: A Different Perspective on a Total Lunar Eclipse

If you were standing on the Moon during a total lunar eclipse, you would see a ring of orange or red light around the Earth where the atmosphere extends into space around our home planet. In essence, you would be watching all of the sunrises and sunsets on Earth at the same time! The dark Earth in front of you would be the parts of the Earth where it is night. On the other side of the Earth, where the sunlight reaches the planet face on, it would be daytime (with blue skies because of the way our atmosphere scatters different wavelengths of light).

The rosy ring around Earth would essentially be places on Earth glanced by sunlight and transitioning from day to night (dusk) on one side, and night to day (dawn) on the other, as the Earth rotates on its axis.

The reason why the Moon turns red during a total lunar eclipse is related to why we have such beautiful pink, orange, and red sunrises and sunsets to enjoy. When we see a sunrise or sunset from our perspective on Earth, sunlight is coming in at a low angle. It has to travel through a lot of atmosphere, scattering more and more blue-colored light as it goes ... until what is left when the light reaches us at these day/night transition times is the more reddish wavelengths that get through.

Mars and the Total Lunar Eclipse

See Mars in the Night Sky!

Simply go outside and look up, contact your local planetarium, or look for a star party near you.

Mars' brightness will match the star Sirius, which is the brightest of all the stars.

The planet will be in the constellation Virgo, 6 degrees north/north-east of the bright star Spica.

As a coincidence, on the same night that Mars is closest to Earth, you can see a total lunar eclipse. With Earth's shadow falling on the full Moon, it will have a reddish color.

See all of the beautiful images of the 2014 Moon Eclipse brought to you by the NASA Lunar Eclipse Group.

Calendar of Total Lunar Eclipses

Did you miss the total Lunar Eclipse on April 15, 2014? Not to worry, here's the future schedule!

April 15, 2014 Americas, Europe, Africa, Asia, Australia
Oct. 8, 2014 Asia, Australia, Pacific, Americas
Sept. 28, 2015 East Pacific, Americas, Europe, Africa, west Asia
Jan. 31, 2018 Asia, Australia, Pacific, West North America
July 27, 2018 South America, Europe, Africa, Asia, Australia
Jan. 21, 2019 Central Pacific, Americas, Europe, Africa
May 16, 2022 Americas, Africa, Europe
Nov. 8, 2022 Pacific, North Americas, Australia, Asia


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