Eclipse Cycles

A similar eclipse to this one took place on May 10, 1994, although this one is shifted about a third of the way westward around the globe. The two eclipses are like cousins — both are members of an eclipse “family,” known as a Saros.

In addition to its month-long cycle of phases, the Moon has several lesser-known cycles, such its distance from Earth and its relation to the Sun’s path across the sky. Three of these cycles overlap every 6,585.3 days (a bit more than 18 years), creating an eclipse.

Each Saros cycle lasts for centuries. It begins with partial eclipses that are visible from one of the poles, then moves across Earth’s disk with total or annular eclipses, then finishes with more partial eclipses at the opposite pole.

The May 20 eclipse is part of Saros cycle 128. The first eclipse in the series took place in the year 984, and the last will be in 2282.

During a total solar eclipse (top), the dark inner portion of the Moon's shadow touches Earth, so the Sun is completely blocked from view. During an annular eclipse, however, the Moon is slightly farther from Earth, so the inner portion of the shadow never reaches Earth's surface. That leaves a ring of sunlight around the intervening Moon.During a total solar eclipse (top), the dark inner portion of the Moon's shadow touches Earth, so the Sun is completely blocked from view. During an annular eclipse, however, the Moon is slightly farther from Earth, so the inner portion of the shadow never reaches Earth's surface. That leaves a ring of sunlight around the intervening Moon.

 

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