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Last updated on April 18, 2014 at 8:17 EDT

What is a Lunar Eclipse?

September 14, 2012

Hi, I’m Emerald Robinson with RedOrbit. In this video we’re going to take a closer look at an astronomical event called a lunar eclipse.

To begin our investigation, it’s important to understand the natural phases of the moon as it revolves around the Earth. These “moon phases” occur over the course of a month, and are due to the moon’s relative location to the Sun with respect to the Earth. This monthly cycle is important, as a lunar eclipse can only occur during a full moon, when it is opposite the Earth from the Sun and fully illuminated.

On rare occassions, the full moon lines up precisely on the ecliptic plane – the plane on which the Earth rotates around the Sun. When this happens, the Earth blocks some or all of the Sun’s light and casts a shadow on the Moon, which we see as a Lunar eclipse.

During a lunar eclipse, the Earth’s shadow has two distinct parts. The umbra is the inner, cone-shaped part of the shadow. It’s the part in which all of the light has been blocked. The penumbra is the outer part of Earth’s shadow, where sunlight is only partially blocked.

Scientists recognize three types of lunar eclipses – Penumbral, Partial and Total.

A penumbral eclipse occurs when only the penumbral shadow is hitting the moon. A penumbral eclipse is very hard to see, because all parts of the Moon are still receiving some light from the Sun.

A partial lunar eclipse happens when a portion of the Moon enters Earth’s umbra, while the rest of the moon remains in the faint light of the penumbra.

In a total lunar eclipse, the moon is entirely in the Earth’s umbra, casting a shadow across its full visible surface.  But even in a total eclipse, the moon remains faintly illuminated by indirect sunlight refracted through the Earth’s atmosphere, giving the moon a faint red glow.

Partial lunar eclipses occur at least twice a year, but total lunar eclipses are less common. If you are lucky enough to see one, be sure to get out your camera as a lunar eclipse provides an opportunity for some amazing photographs.