The Frequency of Lunar Eclipses

A lunar eclipse is a wonderful thing to see. When the moon starts to disappear in the night sky, it must have been viewed with awe, and probably some fear by those who didn’t have the benefit of science to explain what was going on. Today though, we know exactly what is going on when we see the moon disappearing in the night sky. It is simply an eclipse, or when the moon passes through a part of the Earth’s shadow.

There are three types of eclipses that can occur. The first is the penumbral eclipse, or when the Moon passes through the penumbral shadow of the Earth. These are very hard to see, and even with telescopes they can be hard to spot, and so when calculating the amount of eclipses per year, they are not included, as they offer little value to anyone who is not a scientist. About 35 percent of all eclipses fall under this category.

The umbral eclipse, or partial eclipse, is when the Moon passes through the umbral shadow of the Earth. These eclipses are easy to see, and therefore are more easily observed. About 35 percent of eclipses are classified as partial eclipses.

The third type of eclipse is the total eclipse, or when the moon also passes through the umbral shadow. The difference between a partial eclipse, and a total eclipse is the location on the Earth that you happen to be at, and the location of the Moon in relation to the shadows of the Earth. The other 30 percent of eclipses are total eclipses.

A lunar eclipse occurs two to four times every year. A lunar eclipse can only occur during a full moon, and logically you would think that the Moon would eclipse the Earth every month seeing as the orbit of the moon is quite stable.

However the inclination of the orbit of the Moon is tilted at five degrees to the orbital plane of the Earth, meaning that the Moon tends to hover about five degrees below, or above the shadows of the Earth. Also, an eclipse can only be seen by people living on the night side of the Earth, limiting the amount of people who can view an eclipse from Earth.

A lunar eclipse used to be a source of wonder and awe for ancient peoples. Today they still are awe inspiring, but fortunately we can predict them. A lunar eclipse is a regular event, and scientists have calculated every eclipse from 2000BC to the year 3000. For more details on eclipses, including a beginners guide to lunar eclipses, and a complete table of future eclipses go to