How Lunar Eclipses Work

Digital composites like this one are becoming popular ways to capture the progression of phenomena like lunar eclipses. See more moon pictures.
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The moon has been Earth's trusty sidekick for billions of years. And as it endlessly cruises around our planet, once in a while this scrappy satellite precisely aligns within Earth's shadow, taking on an eerie, reddish glow. And what's this phenomenon known as? A lunar eclipse, of course.

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Interest in astronomy stretches back to the Stone Age. Ancient civilizations in Greece, China and Babylonia were fascinated by the celestial events unfolding across the skies above them. Records of eclipses exist in their writings, giving us glimpses of how previous cultures described and interpreted these astronomical happenings. For example, Yuanshi (History of the Yuan Dynasty) details the timing of a total lunar eclipse on May 19, 1277 in traditional double-hours and marks [source: Encyclopaedia Brittanica]. Chinese astronomers used their findings to eventually help predict eclipses with startling precision. In addition, records like the ones detailing lunar eclipses can help pinpoint when, where and how major historical events occurred.

Dating all the way back to 500 B.C., ancient peoples correctly understood the basics of why the moon went through different phases and why eclipses occurred. They often recorded when solar and lunar eclipses took place -- especially when they corresponded to major happenings back on Earth. Typically, they regarded solar eclipses and lunar eclipses as unlucky omens, a frightening sight when either occurred.

In some cases, eclipses impacted the course of history. For example, a lunar eclipse that occurred during the Peloponnesian War enabled the Syracusan army to defeat the Athenians. The eclipse, as both omen and event, greatly frightened and unnerved the Athenian soldiers and sailors so they postponed their intended retreat from Syracuse [source: Encyclopaedia Brittanica]. This delay gave the Syracusan army time to destroy the Athenian forces.

­People have been examining and studying eclipses for 3,000 years, so we better carry on the tradition and learn about the phenomenon for ourselves today. Go to the next page to learn about what happens during a lunar eclipse.