Why don’t we experience lunar eclipse every month?

On Earth, we experience two types of eclipses: A solar eclipse happens when the moon moves between the sun and the earth, blocking out the sun’s rays from reaching the earth and casting its shadow on parts of the Earth.

A lunar eclipse occurs when the moon passes directly behind the earth and the earth’s shadow blocks sunlight from reflecting of the moon. During a total lunar eclipse, the earth’s shadow (umbra) completely covers the moon.

The moon takes approximately 28 days to make one orbit around the Earth. At this point, you may wonder why we don’t have a lunar eclipse every month. That’s because, the orbit of the moon (around the earth) lies in a different plane to that of the earth (around the sun). To be precise, the lunar orbit is inclined by 5.14 degrees to the latter.

For a lunar eclipse to happen, the sun, moon and earth must be aligned. This happens rarely given the differences in the orbit plane. On an average, a lunar eclipse happens three to four times in a year. In 2020, we will experience four lunar eclipses.

 

Picture Credit : Google