The first of two lunar eclipses in 2016 is tonight — here's why they are so rare

The first lunar eclipse of 2016 will take place on Tuesday, March 23. A lunar eclipse takes place when the Earth passes between the Moon and sun. If space were flat, we'd witness a lunar eclipse once a month, but we normally only see two lunar eclipses a year. This brilliant NASA video explains why.

Video courtesy of NASA

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