Rare supermoon eclipse coming: How does it work?
A supermoon will coincide with a total lunar eclipse on Sept. 27, a phenomenon not seen from Earth in more than 30 years.
The rare show will take place over 72 minutes, as Earth's shadow sweeps across the moon as our planet crosses between the sun and moon.聽
The supermoon, or聽what scientists call a perigee, is just optics. The moon does not actually grow any bigger, it only appears that way from Earth because it is slightly closer than usual.
"Because the orbit of the moon is not a perfect circle, the moon is sometimes closer to the Earth than at other times during its orbit," said Noah Petro, deputy project scientist for the Lunar Reconnaissance Orbiter at NASA鈥檚 Goddard Space Flight Center in Greenbelt, Maryland, in a . "When the moon is farthest away, it鈥檚 known as apogee, and when it鈥檚 closest it鈥檚 known as perigee. On Sept. 27, we鈥檙e going to have a perigee full moon 鈥撀爐he closest full moon of the year."
At perigee, the moon will be only 221,753 miles away, compared to its average distance of聽238,900 miles. The relative closeness will make the moon聽look 14 percent larger and 30 percent brighter in the sky than an apogee full moon.
Lunar eclipses typically occur at least twice a year, and 228 will occur in the 21st century alone,聽according to NASA. Lunar eclipses are easy to predict, and the space agency knows the exact timing of eclipses a thousand years into the future. It鈥檚 just a matter of knowing where Earth, the sun, and the moon are at a given point in time, noted Dr. Petro.
As for the supermoon and a lunar eclipse occurring simultaneously, Petro said, "It鈥檚 just planetary dynamics. The orbit of the moon around Earth is inclined to the axis of Earth and the orbital plane of all these things just falls into place every once in a while. When , you might get three to four eclipses in a row or a supermoon and an eclipse happening."
The last supermoon to coincide with a lunar eclipse occurred in 1982, and the next won鈥檛 happen until 2033. "That鈥檚 rare because it鈥檚 something an entire generation may not have seen," said Petro.
And when (and where) exactly should you head outside? The total eclipse will be visible to North and South America, Europe, Africa, and parts of West Asia and the eastern Pacific.
Earth鈥檚 shadow will begin to dim the full moon slightly beginning at 8:11 p.m. EDT. A noticeable shadow will begin to fall on the moon at 9:07 p.m., and the total eclipse will start at 10:11 p.m. The precise moment of perigee will come at 10:00 p.m., and the peak of the eclipse聽鈥� the moment when the centers of the Earth, moon, and sun are all perfectly aligned聽鈥� will be 10:51 p.m.
