What are Lunar Eclipses then?

The Sun isn’t the only object in the sky that gets eclipsed. The Moon can experience an eclipse too.

A solar eclipse occurs when the Moon passes between the Sun and the Earth, blocking the Sun from our view.

Photo: Tom RuenA lunar eclipse occurs when the Moon passes behind the Earth such that the planet blocks the Sun’s rays from striking the Moon. This happens when the Sun, Earth and Moon are aligned with the Earth in the middle.

Since the Moon doesn’t produce its own light, and that what we see in the nightsky is really the Moon reflecting light from the Sun, as it passes behind the Earth and into its shadow, the Moon becomes dark.

There are different types of lunar eclipses. Before we begin, the shadow of the Earth can be divided into two distinctive parts: the umbra and the penumbra. Within the umbra, there is no direct solar radiation. However, as a result of the Sun’s large angular size, solar illumination is only partially blocked in the outer portion of the Earth’s shadow, which is given the name penumbra.

  • penumbral eclipse occurs when the Moon passes through the Earth’s penumbra. The penumbra causes a subtle darkening of the Moon’s surface. A special type of penumbral eclipse is a total penumbral eclipse, during which the Moon lies exclusively within the Earth’s penumbra. Total penumbral eclipses are rare, and when these occur, that portion of the Moon which is closest to the umbra can appear somewhat darker than the rest of the Moon.
  • partial lunar eclipse occurs when only a portion of the Moon enters the umbra.

Author: Tom Ruen

  • When the Moon travels completely into the Earth’s umbra, one observes a total lunar eclipse. The Moon’s speed through the shadow is about one kilometer per second and totality may last up to nearly 107 minutes. Nevertheless, the total time between the Moon’s first and last contact with the shadow is much longer, and could last up to 3.8 hours. The relative distance of the Moon from the Earth at the time of an eclipse can affect the eclipse’s duration. In particular, when the Moon is near its apogee, the farthest point from the Earth in its orbit, its orbital speed is the slowest. The diameter of the umbra does not decrease much with distance. Thus, a totally-eclipsed Moon occurring near apogee will lengthen the duration of totality.
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