Tonight, the southern portion of the moon will pass through Earth's outer shadow causing a partial lunar eclipse. You'll have to look very closely and be geographically lucky, however, if you want to see the show.

Tonight's event is called a penumbral lunar eclipse. It is caused when part of the moon passes through the edge of earth's shadow. The name comes from the Latin word for "almost shade," penumbra. When any shadow is formed, the solid, dark part of the shadow is called the umbra, from the Latin word for "shade," while the fuzzy edge of the shadow is called the penumbra. A penumbra cast by an object as far away as the moon is from the Earth (an average of 238,000 miles or 384,400 kilometers) is very wide.

Shading will be subtle, but the moon will be under partial shadow for about four hours. Maximum eclipse will occur tonight at 7:50 p.m. EDT/ 6:50 p.m. CDT (2350 GMT).

Sky gazers in North America or South America will see the best show at moonrise, which is the same time as sunset. According to Discovery, this will, unfortunately, make the eclipse hard to see "because we will be looking for a slight dimming of the moon which is already dimmed by passing through a great deal of the Earth's atmosphere."

You stand a better chance of seeing the astronomical phenomenon if you live farther north and east.

In Los Angeles, the moon rises at 6:09 p.m. PDT, over an hour after maximum eclipse. Therefore, Los Angelites will miss the show. In New York City, on the other hand, moonrise is at 5:59 p.m. EDT at an altitude of 20 degrees during maximum eclipse. In Chicago, moonrise is at 5:54 p.m. CDT during with a maximum eclipse altitude of 9 degrees. These are better conditions for seeing the eclipse.

The eclipse will also be visible from western Asia, Africa and Europe. For them, the show begins when the moon is overhead in the middle of the night. "The partial shading will be visible as a slight reddish dimming of the normally bright full moon," Discovery reports.

If you are not in a good location to see the penumbral lunar eclipse, don't worry; the Internet's got you covered. There will be a live penumbral eclipse webcast on SPACE.com, courtesy of Slooh.

"Although a penumbral lunar eclipse might go unnoticed by someone casually glancing at the moon, we will be able to observe the gradual shading of the moon in the live images Slooh will broadcast throughout the eclipse," Slooh's Paul Cox said in a statement. "The shading becomes far more apparent when viewed as a time-lapse, and we'll show viewers that during the live segment of the show."

Check out photos of a penumbral lunar eclipse here.