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Tonight, a supermoon will shine red with the blood of the innocent

Actually it's just refracted light from the Sun

David McNew/Getty Images

This Sunday, the Moon will provide a big, bloody show for those looking up into the night sky. A total lunar eclipse — sometimes referred to as a blood moon due to the Moon's dark red glow — is scheduled to begin at 10:11PM ET on Sunday.

But this eclipse is particularly special, because it's happening on a night when the Moon will also be a supermoon. That's when a full moon occurs on the same night of the Moon's perigee, or the time when the Moon is closest to Earth. The Moon has an elliptical orbit around our planet, so its distance from Earth doesn't stay the same. When at perigee, the Moon looks up to 14 percent larger and 30 percent brighter than it does when it's at apogee (its farthest point from Earth).

The last time this happened was more than 30 years ago

So Sunday's lunar eclipse is going to be very big, very round, and very red. A super blood moon. The last time that happened was more than 30 years ago. The next time it will happen is sometime in 2033.

Normally, we see the Moon at night because it reflects light coming from our Sun. But during a lunar eclipse, the Moon passes directly behind Earth into our planet's shadow, or umbra; this can only happen when the Sun, Earth, and Moon are in complete alignment. As a result, our planet blocks most of the Sun's light from reaching the Moon.

Some sunlight still makes it through, however, which is why lunar eclipses glow red. The light passing through the atmosphere around Earth's "edges" gets refracted — or redirected onto the Moon. The air molecules in the atmosphere also cause the light to scatter. Shorter wavelengths are more likely to be scattered while longer wavelengths — like red — make it through. It's the same effect we see during sunrise and sunset, when the sky looks reddish and orange.

People in South America and on the East Coast of the United States will have the best seats to the super blood moon show, according to NASA. The space agency's top photographer also has some great tips about how to capture the eclipse with your camera. The entire event is scheduled to start just after 8PM ET on Sunday, when the Earth's shadow starts creeping over the Moon. The total lunar eclipse will begin at 10:11PM ET and peak at 10:47PM EDT. This red phase should last an hour and 11 minutes, so we'll have our grey Moon back to normal after 11:30PM ET.

Correction: Red light has longer wavelengths than most colors in the visible spectrum; a previous version of this story suggested red wavelengths were short.