Sunday's Supermoon: Overhyped?
The nearside of the moon. Photo by the Lunar Reconnaissance Orbiter Camera.
A message to the skywatchers: tilt your head back after nightfall on Sunday, and you'll see the closest full moon of the year -- a phenomenon known as a "supermoon."
Except it's not all that super, and it's not really a phenomenon. In fact, the term "supermoon" was coined not by a scientist, but by an astrologer. And unless you're uniquely in tune with the brightness and largeness of the moon on other nights, you likely won't notice a difference.
But, NASA scientists say, any excuse to look at the moon makes up for the lack of geophysical significance.
But let's back up. The moon takes an elliptical shape as it orbits the Earth, which means once every month it is closer to Earth than normal - that's known as perigee. On Sunday, the moon will be 10 percent closer than an average perigee -- the closest all year -- and about 12 percent bigger.
But can the human eye discern a 12 percent difference?
"Not really," said Michelle Thaller, an astronomer at NASA's Goddard Spaceflight Center. "The human eye can't really pick that out. It's going to be a beautiful, bright, slightly larger full moon."
There is no correlation between a supermoon and any sort of disaster as some have suggested, like an earthquake or tidal wave, she stressed. Though it could make tides about an inch higher.
Still, it's a good excuse for moonwatching. So in the spirit of the occasion, we have some tips from lunar scientists on how to look at the moon.
In the Northern hemisphere, we talk about the man on the moon -- volcanic markings that some say look like a face. But the southern hemisphere -- Australia, for example -- sees the moon upside down relative to the U.S. There, they say it looks like a rabbit or a frog, Thaller said.
The dark spots on the moon are lava flows -- volcanic plains that formed 2 to 3 billion years ago. Asteroids slammed into the moon, cracking it's crust, and lava flowed up, filling huge empty space. That's now made up of big lava plains, dark because they have the reflectivity of a lump of coal.
In the moon's brighter regions, you're seeing the ancient crust that formed 4.5 billion years ago. And then there are the lunar craters, bowl-shaped depressions, formed also by large impacts from asteroids crashing into the moon's surface.
"On Earth, you don't have a lot of old rocks that go back that far," said Noah Petro, a research scientist at the NASA Goddard Spaceflight Center. "Because we have wind and weather and rain and plate tectonics, the crust of the Earth gets recycled."
But on the moon, these features are preserved over 3 or 4 billion years.
"Just looking at the moon, you see the history of the solar system," Thaller said. "You see things hitting and cracking the crust of the moon."
So has the supermoon been overhyped?
"As part of the machine that's overhyping it, yes and no," Petro said. Although the supermoon will have no real geophyiscal impact, "it's a day during the year that we can talk about the moon, which is really important."
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Rebecca Jacobson, Patti Parson and David Pelcyger contributed to this report.