Moon at Perigee: Supermoon

There has been a lot of hype in the media lately about the full moon on November 14 - that it will be the closest supermoon since 1948. So what is the deal with the supermoon anyway?

Image Source

What's so super about this full moon? 

The Moon is not going to be actually bigger than usual, just like when it phases it does not actually change shape. Rather, it will appear slightly larger in our sky. The Moon does not orbit the Earth in a perfect circle. Because its orbit is just slightly elliptical, or oval-shaped, sometimes the Moon is closer to the Earth than and sometimes it is farther. Astronomers say the Moon is at perigee when it is at its closest point in its orbit, and apogee when it is at its farthest point. Since those words don't mean much to non-astronomers, and don't sound very interesting, sometimes the full moon at perigee is referred to as a supermoon, and sometimes the apogee Moon is referred to as a minimoon. This year the full moon will be at perigee in October, November, and December. When the Moon is a little closer to Earth, it looks slightly bigger in the sky - but you really have to pay attention to notice, especially when you can't compare them side by side, as in the graphic below. 

My friend Jason from the Boonshoft Museum of Discovery made this helpful graphic comparing the sizes of three full moons this year. As you can see, the November and December full moon will look larger than the one in May.

The full moon on November 14 will be the closest one of the year, only 221,524 miles away. (On average, the Moon is 238,900 miles away). It will not be until November 25, 2034, that a full moon will be closer to the Earth than the one this November.

Rising full moon in Blue Canyon. Image Source

If you want to observe the beautiful full moon in November, I recommend watching moonrise (5:18 pm on November 14). The Moon always looks larger when it is along the horizon, due to an optical illusion. It also often looks yellow or orange as it is rising, because when it is low on the horizon there are more layers of atmosphere between the viewer and the Moon for the moonlight to pass through. The air scatters the blue, green, and purple visible light, so the Moon often looks yellow, orange, or red. The rising full moon is a beautiful sight. 

Image: Stellarium and Me

So enjoy observing the Moon tonight! Look for the bright planet Venus in the southwest at sunset, and orangish-red Mars in the south. See what bright stars you can find through the Moon's light - look for the summer triangle, or the Big Dipper low in the northwest. Remember, you can always learn the latest news from space at the Dome Planetarium! Follow the us on Facebook or Twitter for daily updates, and come see a show next time you visit the Peoria Riverfront Museum - we teach about space and science everyday.