October 'Supermoon' Lighting Up Weekend Sky Right Now

If you're under clear skies where you are tonight — the forecast is "mostly" clear — then you're under a very bright full moon. The October full moon, which is also a hunter’s moon, is the first of three supermoons that will close out the year, with the trifecta continuing in November and December.

The moon will be especially bright because it’s near perigee. What’s that, you who slacked in science class, ask? “Supermoon” is the unofficial term for “perigee,” when a full moon coincides with the moon’s closest approach to Earth in its oval-shaped orbit, making it appear 14 percent bigger in the night sky and often taking on an orange hue.

Are supermoons just hype? Yes and no. Supermoons aren’t really larger, but they only appear so because the moon is so close to the Earth. But, Earthsky.org says, “they can cause real physical effects, such as larger-than-usual tides.”

Also, the orange color of the moon near the horizon “is a true physical effect.”

“It stems from the fact that — when you look toward the horizon — you are looking through a greater thickness of Earth’s atmosphere than when you gaze up and overhead. The atmosphere scatters blue light – that’s why the sky looks blue,” Earthsky.org says. The greater thickness of atmosphere in the direction of a horizon scatters blue light most effectively, but it lets red light pass through to your eyes. So a moon near the horizon takes on a yellow or orange or reddish hue.”

October’s supermoon is a sort of warm-up event for the Nov. 14 supermoon, which will be the closest to the Earth of any supermoon so far in the 21st century. Earthysky.org says a moon won’t be as close to Earth again until Nov. 25, 2034, and that in the Americas, the best night to view it may be Nov. 13 instead of Nov. 14.

• See Also: 2016 Meteor Shower Guide

Astrophysicist Fred Espenak, a NASA scientist emeritus, lists the Oct. 16, Nov. 14 and Dec. 13 full moons as supermoons, and also includes the January 2017 full moon on the list. Their disagreement comes from ambiguity on how “90 percent of perigee” is measured.

Supermoons during the winter months tend to look larger than Supermoons that occur during the rest of the year in the Northern Hemisphere. At this time of the year, the Earth is closer to the Sun. Because of this, the Sun's gravity pulls the Moon closer to Earth, making any winter Super Full Moons look bigger than summer Perigee Moons.

Written by Beth Dalbey and Deb Belt | Photo by Derek Keats via Flickr Commons