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Lunar Eclipses for Beginners
What is a lunar eclipse? What causes eclipses? How often do eclipses happen and when is the next lunar eclipse? You'll find the answers to these questions and more on this site on lunar eclipses.
NASA
Nasa: Eclipses
The periodicity and recurrance of eclipses is governed by the Saros cycle, a period of approximately 6,585.3 days (18 years 11 days 8 hours). It was known to the Chaldeans as a period when lunar eclipses seem to repeat themselves, but...