Look skyward overnight Sunday and early Monday and you're in for a treat: A brighter, larger full moon than usual. It's called a supermoon, and this one's especially super.
A supermoon occurs when two things happen at the same time: The moon is full - and at the closest point to earth in its elliptical orbit. That's called "perigee."
Supermoons actually aren't all that rare - we see 4 to 6 a year. But the moon's orbit shifts. And this time, the full moon hits just as its orbit is at the closest point in 68 years.
“The last time it appeared this big, the last time it reached its full phase, near perigee, as it will on Sunday night and into Monday morning, was actually in 1948. And the next time we'll see it this big again won't be until 2034,” said astronomer Kristen Thompson of Davidson College.
This supermoon will appear 14 percent larger, and 30 percent brighter, than a typical full moon.
The effect is magnified if you watch at on the horizon, at moonrise or moonset, Thompson said. That's because of the "moon illusion." The moon always looks bigger beside trees or buildings at the horizon, but it's just a brain trick.
The actual moment of the supermoon is early Monday, but that's not the only time to see it.
“Any clear night over the weekend and into early next week, you'll be able see a full moon that's going to be brighter and larger than the average full moon,” said NASA planetary scientist Noah Petro.
Moonrise is just after 5 p.m. Sunday. It sets Monday around 6:45 a.m.
Slooh Community Observatory (http://live.slooh.com/) will stream the supermoon – which they’re calling a “Mega Beaver Moon”- live on the web. It’s a network of telescopes linked on the web.
NASA.gov, “2016 Ends with Three Supermoons.” https://science.nasa.gov/news-articles/2016-ends-with-three-supermoons