You’ve heard the expression “once in a blue moon,” but what about “once in a supermoon”?
On Saturday night, the sky will be filled with just that — a supermoon, or more technically a “perigee” moon, a Greek term to describe the point when an orbiting object is closest to Earth.
Of course, the moon is the same size it’s always been (about 2,150 miles in diameter), but it will appear about 14 percent bigger and 30 percent brighter than usual because it’s passing so close to Earth, according to NASA’s website.
“The moon’s orbit is not a perfect circle; it is slightly elliptical,” said Manfred Cuntz, director of astronomy and associate professor of physics at the University of Texas at Arlington. “It happens now that the time that the moon is really close to the earth is also a full moon.”
Cuntz said perigree and blue moons don’t have much in common — aside from the fact that both are full.
“Some months have 28 days, and others have 30 or 31. Because the orbit of the moon takes 27 days, we usually have one full moon per month, but occasionally we have two. In this case, the second full moon is called a blue moon,” he said.
Cuntz said that these full moons are even rarer than blue moons, which happen about once every 2 1/2 years. The last supermoon was recorded in 1993, and the next one won’t occur until 2029.
With any luck, North Texans won’t have to wait another 18 years to see the close encounter. But cloudy conditions expected Saturday could spoil the show.
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