tonight we will be treated to a total lunar eclipse!!!! this occurs when the sun is on one side of the earth and the moon is directly on the other side. the moon is full during a lunar eclipse since the sun illuminates it entirely from our view on earth. the three bodies line up in a perfect line, so that the shadow of the earth, created by the sun, passes right over the full moon.
the picture below (that came from stardate) shows the path of the moon thru the shadow of the earth. the darkest part of the shadow, the umbra, is shown as the dark red circle. the penumbra shows a ring of partial shadow. when the moon passes thru this area, it shows a faint orange color.
the challenge with this lunar eclipse is that it starts at 3 am!!! by 5am, the moon will be fully immersed in the umbra region and this portion of the total eclipse will last until about 6:30am. so you can either stay up super late or wake up early to see this astronomical phenomenon. enjoy!!
there's more info at NASA's eclipse page and an animation i found from a 2003 eclipse....