Super Full Moon to Grace the Skies Tonight

March 19, 2011— -- When you step outside tonight, don't forget to take a good look up at the sky.

Assuming clouds don't get in the way, you'll get to gaze at the biggest full moon in nearly two decades.

During what some skywatchers are calling the "supermoon," the moon won't just be at its closest approach to Earth in its elliptical orbit, it will be closer than it has been in 18 years.

"It's going to be big and really bright," said NASA astronomer Dave Williams. "It should be noticeably brighter than a normal full moon."

Full moons come in different sizes because of the elliptical shape of the moon's orbit -- one side of the ellipse is about 31,000 miles closer to Earth than the other. When the moon is closest to Earth (at its perigee), it is 14 percent larger and 30 percent brighter than when it's farthest from the planet (at its apogee).

For weeks, the rare full moon has sparked interest online, with astrologers and amateur astronomers speculating that the "supermoon" could lead to unusual weather. After Japan's earthquake, some even wondered if the supermoon contributed to the event.

In a post earlier this month, Accuweather blogger MarkPaquette said the phrase "supermoon" originated on the website of astrologer Richard Nolle and spread to astronomers online.

According to Nolle's definition, a new or full moon at 90 percent or more of its perigee (or closest approach to Earth) qualifies as a "supermoon." Tonight's full moon won't just be a supermoon but an extreme supermoon, he said, because the moon will be almost precisely at its closest distance to Earth.

According to "new age" forecasts, he said, the supermoon brings strong earthquakes, storms or unusual climate patterns.

"There were supermoons in 1955, 1974, 1992 and 2005," Paquette wrote. "These years had their share of extreme weather and other natural events. Is the Super Moon and these natural occurrences a coincidence?

But scientists emphasize that there is no connection between the moon's position and extreme weather or natural disasters (like Japan's earthquake) here on Earth.

"There's nothing really special about this," NASA's Williams told ABCNews.com.