Earth’s shadow can be divided into two distinctive parts: the umbra and penumbra.

Earth totally occludes direct solar radiation within the umbra, the central region of the shadow. However, since the Sun’s diameter appears about one-quarter of Earth’s in the lunar sky, the planet only partially blocks direct sunlight within the penumbra, the outer portion of the shadow.

Within the umbra, the central region, the planet totally shields direct sunlight. In contrast, within the penumbra, the outer portion, the sunlight is only partially blocked.

In the diagram, the Sun, Moon, and Earth sizes nor the distances between the bodies are to scale.

Total Lunar Eclipse

This occurs when the moon falls entirely within the earth’s umbra. Just prior to complete entry, the brightness of the lunar limb– the curved edge of the moon still being hit by direct sunlight– will cause the rest of the moon to appear comparatively dim. The moment the moon enters a complete eclipse, the entire surface will become more or less uniformly bright.

Later, as the moon’s opposite limb is struck by sunlight, the overall disk will again become obscured. This is because as viewed from the Earth, the brightness of a lunar limb is generally greater than that of the rest of the surface due to reflections from the many surface irregularities within the limb: sunlight striking these irregularities is always reflected back in greater quantities than that striking more central parts, and is why the edges of full moons generally appear brighter than the rest of the lunar surface. This is similar to the effect of velvet fabric over a convex curved surface which to an observer will appear darkest at the center of the curve. It will be true of any planetary body with little or no atmosphere and an irregular cratered surface (e.g., Mercury) when viewed opposite the Sun.

Partial Lunar Eclipse

A partial lunar eclipse occurs when only a portion of the Moon passes through the Earth’s darkest shadow. During this type of eclipse, a part of the Moon will darken to a dim orange or red as it moves through the Earth’s shadow.

A partial lunar eclipse occurs when only a portion of the Moon enters Earth’s umbra, while a total lunar eclipse occurs when the entire Moon enters the planet’s umbra. The Moon’s average orbital speed is about 1.03 km/s (2,300 mph), or a little more than its diameter per hour, so totality may last up to nearly 107 minutes. Nevertheless, the total time between the first and the last contacts of the Moon’s limb with Earth’s shadow is much longer and could last up to 236 minutes.

Central Lunar Eclipse

This is a total lunar eclipse during which the Moon passes through the center of Earth’s shadow, contacting the antisolar point. This type of lunar eclipse is relatively rare.

The relative distance of the Moon from Earth at the time of an eclipse can affect the eclipse’s duration. In particular, when the Moon is near apogee, the farthest point from Earth in its orbit, its orbital speed is the slowest. The diameter of Earth’s umbra does not decrease appreciably within the changes in the Moon’s orbital distance. Thus, the concurrence of a totally eclipsed Moon near apogee will lengthen the duration of totality.

Penumbral Lunar Eclipse

This occurs when the Moon passes through Earth’s penumbra. The penumbra causes a subtle dimming of the lunar surface, which is only visible to the naked eye when about 70% of the Moon’s diameter has been immersed into Earth’s penumbra. A special type of penumbral eclipse is a total penumbral lunar eclipse, during which the Moon lies exclusively within Earth’s penumbra. Total penumbral eclipses are rare, and when these occur, the portion of the Moon closest to the umbra may appear slightly darker than the rest of the lunar disk.