During a solar eclipse, the moon passes between the Earth and the sun, and its shadow blocks the light coming from the sun. Twice a year, during what is called an eclipse season, the moon crosses into Earth's orbit; this is the only time that an eclipse can happen. In addition, the moon must be in its new-moon phase for an eclipse to take place. As a result of the very specific alignment of the Earth, moon and sun that is required, solar eclipses are infrequent occurrences.
Because a solar eclipse is so rare, people are tempted to sneak a peek, assuming that a quick glance won't do any harm. However, permanent damage can be caused to the retina after just a few seconds. The human eye includes a lens; staring at the sun causes the lens to focus sunlight toward a particular point on the retina. As a result, the light's intensity kills off retinal cells, which can cause blindness.
Staring at partial solar eclipses also can hurt your eyes, maybe even the rare midnight solar eclipse. Of course, you'd have to be in the Arctic in midsummer, or maybe in northernmost Europe, Asia or North America to see one. It happens only in the Arctic because of the long summer days. Amazingly, a partial midnight solar eclipse in June 2011 stated on a Thursday and ended on a Wednesday. That's because the moon's shadow moved eastward across the International Date Line, so the eclipse started on a Thursday morning in northeast Asia and ended on a Wednesday evening over Greenland and Iceland [source: MSNBC].
NASA maintains a list of upcoming solar eclipses, along with mentions of eclipses throughout history. It's no wonder ancient people had trouble understanding these seemingly random and frightening events. Typically, a solar eclipse only occurs about every 375 years in a single place, but it can be about 600 years or as little as 65 years between locations [source: Mr. Eclipse].
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