You can see the first lunar eclipse of 2020 on January 10. A lunar eclipse occurs when the moon is opposite the sun, and the earth, which is positioned in between, casts its shadow on the moon. It only occurs when there is a full moon but not necessarily every full moon. A lunar eclipse can occur thrice in a year. In the 21st century, there was a total of 85 eclipses. At its maximum, an eclipse can last for three hours and 40 minutes.