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| Space on Jun 10, 2012

Five best things to see during a lunar eclipse, from the moon

If you could stand on the surface of the moon during a total lunar eclipse, you’d be bathed in an eerie red glow. What else would you see?

An eclipse of the moon takes place when the sun, Earth and moon line up in space, with Earth in the middle. Earth’s shadow falls on the moon. This sort of eclipse is an awesome sight, lasting several hours. During totality, we on Earth see the surface of the moon turn fiery red as Earth’s shadow covers it completely. But what would this same eclipse look like as seen from the moon’s surface?

A lunar eclipse takes place when the sun, Earth and moon line up in space. The moon passes through Earth's shadow. (Wikimedia Commons)

One side of the moon always faces Earth. To experience an eclipse from the moon, you’d have to be standing on that Earth-facing side. From the moon, during what we see as a lunar eclipse from Earth, you on the moon would see the Earth eclipse the sun.

Here are the five best things to see during an eclipse, as seen from the moon.

1. Eerie red glow on surrounding moonscape. During an eclipse of the moon – aka an eclipse of sun by Earth, seen from moon – if you were standing on the moon’s surface, you’d be bathed in an eerie red light. What is it? It’s sunlight – scattered and bent during its passage through Earth’s atmosphere – that has found its way onto the lunar surface. In other words, even when Earth blocks the sun from view, some sunlight still finds its way through Earth’s atmosphere onto the surface of the moon.

Artist's concept of lunar eclipse as seen from moon. Notice that the moon's surface is red and that the Earth covers the sun more completely than the moon does during a solar eclipse seen from Earth. (Wikimedia Commons)

Painting of eclipsed moon, above, by Lucien Rudaux (1874 – 1947).

Why does the moon look red during a total lunar eclipse?

2. Big ol’ Earth. A cool thing about solar eclipses seen from Earth is that the sun and moon appear so nearly alike in size in our sky, even though the sun is really 400 times wider in diameter than the moon. But – as seen from the moon – Earth appears bigger than the sun. That’s because Earth is bigger than the moon (Earth’s radius is 6,378 kilometers; the moon’s radius is 1,737 kilometers). Earth as seen from the moon appears nearly four times bigger than the moon seen in our sky. So, if you were standing on the moon’s surface during a lunar eclipse, the Earth – in front of the sun – would look much bigger than the moon during a total solar eclipse seen from Earth.

3. Night side of Earth in lunar sky. This one is really more about what you’d see before and after the eclipse, but it’s still interesting. Here are the three relevant facts. First, Earth hangs in one spot in the sky, as seen from the side of the moon that always faces Earth. Second, the sun appears to move across the lunar sky, taking about two weeks to go from sunrise to sunset. Third, the moon doesn’t have an atmosphere. What does it all mean? It means that – if you were standing on the moon’s surface – you’d see the Earth, the sun and the stars all at once, in the same sky. During a lunar eclipse seen from the moon’s surface, the Earth would appear at the new phase, corresponding to new moon. You wouldn’t see any of Earth’s day side. You’d only see Earth’s night side. In the days before the eclipse – as the sun crept closer to Earth in the lunar sky – you’d see the blazing sun near the night disk of Earth, perhaps with some sliver of illumination visible. This dark Earth would be blotting out the stars.

Eclipse of sun by Earth, as seen by Japan's Kaguya moon probe on February 10, 2009. The ring appears incomplete at the bottom because the limb of the moon, on the moon's night side, is obscuring the view. Credit: JAXA/NHK.

Click here to expand image above.

4. A very looooong eclipse. Eclipses last longer seen from the moon than from Earth. They last longer because Earth appears nearly four times larger than the sun on the lunar sky dome. It’s that big ol’ Earth again: see #2 above. Exactly how long an eclipse lasts as seen from the moon depends on how centrally the sun passes behind the Earth, but, generally speaking, the sun might take about five hours to pass entirely behind the Earth. That’s in contrast to about three hours total for a lunar eclipse seen from Earth. Watching an eclipse from the moon? Bring a lunch.

5. A red arc of sunrises and sunsets around Earth. As you stood on the moon and watched the sun disappear behind the Earth, the sun would grow fainter and redder. At the total phase of the eclipse, you would see a glowing, reddish arc – or even a complete red ring – illuminating the circumference of the Earth. You would be seeing the line of sunsets and sunrises on Earth – a rare and beautiful sight which would persist throughout the eclipse totality.

There you have it, a lunar eclipse seen from the surface of the moon. It’s lots of fun to imagine, and, someday, someone will see one!