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Sunday's 'supermoon eclipse' will not reappear until 2033, professor says

Thursday, September 24, 2015

LAWRENCE — On Sunday evening, Sept. 27, for the fourth time since April 2014, observers will have the opportunity to see the moon totally eclipsed by the Earth.

Lunar eclipses occur when the sun, Earth and moon line up along a straight line, allowing the moon to pass within the Earth’s shadow at full moon. Because of the relative tilt of the moon’s orbit about the Earth and the Earth’s orbit about the sun, eclipses don’t occur every month. 

For observers in the Midwest, partial eclipse will begin at 8:07 p.m., with total coverage of the moon running from 9:11 p.m. to 10:23 p.m.  The partial eclipse ends at 11:27 p.m. 

Bruce Twarog, professor of physics and astronomy at the University of Kansas, is available to speak to media about the event. Twarog also advises the Astronomy Associates of Lawrence, an organization of people with an interest in astronomy that is open to the public at-large.

“This is being referred to as a ‘supermoon eclipse’ because it takes place when the moon appears larger in the sky than usual, about 13 percent larger than it was during the eclipse in April 2015,” Twarog said. “Because the moon’s orbit is noncircular, its distance from the Earth varies, so the angle it fills in the sky increases when it’s closer and declines when it’s further away. It just so happens that the moon will be at perigee  — closest approach to Earth — and biggest in the sky about an hour before the middle of the eclipse.”

A similar supermoon eclipse won’t occur again until the next tetrad in 2033, he said.

According to Twarog, total lunar eclipses will occur about two weeks after a solar eclipse but, typically, less than five total lunar eclipses are expected every decade. He said the tetrad of four eclipses since April 2014 is unusual but still just a result of the combination of the Earth-sun and Earth-moon orbital tilt and orientation. Though uncommon, tetrads will occur eight times between 2000 and 2100, with the next scheduled for 2032-33. What makes this eclipse more unusual is the size of the moon in the sky at the time of the eclipse, Twarog said.

“The beauty of a lunar eclipse is that no observing equipment, telescope or binoculars, is required. If you can see the moon, you can see the eclipse,” he said.

Photo by Adrian Scottow, via WikiCommons