from Mr. Eclipse.com and Prentice Hall Planet Diary

An eclipse of the Moon (or lunar eclipse) can only occur at Full Moon, and only if the Moon passes through some portion of the Earth's shadow. The shadow is actually composed of two cone-shaped components, one nested inside the other. The outer or penumbral shadow is a zone where the Earth blocks part but not all of the Sun's rays from reaching the Moon. In contrast, the inner or umbral shadow is a region where the Earth blocks all direct sunlight from reaching the Moon.

Astronomers recognize three basic types of lunar eclipses:

1. Penumbral Lunar Eclipse

• The Moon passes through Earth's penumbral shadow.
• These events are of only academic interest since they are subtle and quite difficult to observe.

2. Partial Lunar Eclipse

• A portion of the Moon passes through Earth's umbral shadow.
• These events are easy to see, even with the unaided eye.

3. Total Lunar Eclipse

• The entire Moon passes through Earth's umbral shadow.
• These events are quite striking for the vibrant range of colors the Moon can take on during the total phase (i.e. - totality).