Why does the Moon turn red during a total lunar eclipse? NASA experts explain.

This is what happens between the light of the Sun and our atmosphere so that during a total lunar eclipse we can see from Earth what is known as a "Blood Moon."

Why does the Moon turn red during a total lunar eclipse?
Why does the Moon turn red during a total lunar eclipse?

The Moon will pass through Earth's shadow and appear red on the night of March 13 (or the early morning of March 14, depending on your time zone). Here's what you need to know about this total lunar eclipse to discover why the lunar disk turns red during a total eclipse.

What is a lunar eclipse?

When the Moon is within the umbra, it appears orange-red . Lunar eclipses are sometimes known as “blood moons” because of this phenomenon.

When the Moon is within the umbra, it appears orange-red. Lunar eclipses are sometimes known as “blood moons” because of this phenomenon.

Why does the Moon turn red during a lunar eclipse?

According to NASA experts, the same phenomenon that makes our skies blue and our sunsets red causes the Moon to turn reddish-orange during a lunar eclipse.

Sunlight looks white, but it actually contains a rainbow of components , and different colors of light have different physical properties. Blue light scatters relatively easily as it passes through Earth's atmosphere. Reddish light, on the other hand, travels more directly through the air.

When the sun is high overhead on a clear day, we see blue light scattered across the sky above us. At sunrise and sunset, when the sun is near the horizon, incoming sunlight travels a longer path at a low angle through Earth's atmosphere to observers on the ground. The bluest part of the sunlight is scattered far into the distance (where it is still daytime), and only the yellow to red portion of the spectrum reaches our eyes.

Total lunar eclipse of March 13-14, 2025
Map showing the visible location of the lunar eclipse on March 13–14, 2025. The contours mark the edge of the visible region during the eclipse's contact times, identified with Universal Time (UTC). Credit: NASA Scientific Visualization Studio.

During a lunar eclipse, the Moon appears red or orange because all sunlight not blocked by our planet is filtered through a thick layer of Earth's atmosphere on its way to the lunar surface. It's as if all the sunrises and sunsets in the world were projected onto the Moon.

When the Earth's shadow covers the Moon, it not only turns red, it also freezes rapidly. During an eclipse, the lunar surface temperature can drop precipitously in a matter of hours , according to measurements taken during the Apollo missions.

The temperature on the lunar surface during an eclipse ranged from 93°C to -128°C. "During a lunar eclipse, the temperature swing is so dramatic that it's as if the surface of the Moon went from being in an oven to a freezer in just a few hours," explains scientist Noah Petro of NASA's Lunar Reconnaissance Orbiter.

What else can I observe during the night of this eclipse?

Look to the western sky on the night of the eclipse to catch a glimpse of the planets Jupiter and Mars . At the beginning of the eclipse, the Moon will be in the constellation Leo, under the lion's hind leg; shortly after, it will cross the sky to the constellation Virgo.

As the Earth's shadow dims the Moon's brightness, it may be easier than usual to spot the constellations.