Weekend “Black Hole” Full Moon Brightest And Closest Of The Year

Watch for a bigger and brighter full moon than usual tomorrow and Sunday nights. Photo illustration: Bob King

Wishing you a grand first day of summer today and clear nights ahead. This weekend we’ll see the full moon dangling like heavy fruit low in the southern sky. If it looks a tad bigger than last month’s Full Flower Moon, it really is. The moon reaches perigee – closest point to Earth in its orbit – at 6:11 a.m. CDT Sunday morning June 23 just a half hour before the moment of full moon. At the same time it will hover in front of the Milky Way’s central supermassive black hole.

With all those superlatives, you might think I’m setting you up for the end of the world. Trust me, I’m not. The full moon is near the same spot every June and perigees are almost as common as dandelions.

Like the planets do around the sun, the moon moves in an elliptical orbit around the Earth. Once a month it’s closest to us at perigee and farthest away at apogee. Next apogee will be at new moon on July 7. The moon’s average distance from Earth is 238,856 miles (384403 km).

The moon follows an elliptical path around the Earth with one side of its orbit some 31,000 miles (50,000 km) closer (perigee) to our planet than the other side (apogee). Since the moon orbits the Earth every 27 days it reaches perigee once or sometimes twice a month.

So what makes this one special? Well, not all perigees are alike. Some are closer than others and occur at times other than full moon. The closest perigees, like this Sunday’s, occur when the moon is either full or new – times when Earth, moon and sun are all lined up in a row. The sun’s gravity tugs more strongly on the moon at these phases, stretching its orbit and leading to extreme values for perigee and apogee.

No one notices an unusually large first quarter or crescent moon, but we all sit up and pay attention to a bigger-than-normal full moon.

The difference between the the moon at its most distant apogee and closest perigee dramatically illustrated in this pair of photos taken in 2006. The full moon can be as much as 14% bigger and 30% brighter when closest. The weekend’s moon will be 12% bigger than January 2014’s apogee full moon. Credit: Anthony Ayiomamitis

The moon’s most distant perigee (230,000 miles) happened at last quarter phase on March 5 this year. Sunday’s will be the closest of the year at just 222,000 miles (357,000 km). Some keen-eyed skywatchers might notice the moon looking a little larger than it will at apogee on Jan 14, 2014. I say might. Without a reference, it’s terribly hard to compare sizes. The moon illusion, an apparent bloating of our satellite when seen low in the sky, further complicates the view. Still, facts are facts. The moon will be bigger and brighter this weekend than on any other night this year.

Saturday night’s full “Black Hole Moon” will lie about one fist held at arm’s length left and above the center of Milky Way galaxy.  Astronomers call the spot Sagittarius A* (Sagittarius A star). Blocked by intervening dust and invisible to optical telescopes, it marks the site of a supermassive black hole. Created with Stellarium

Not only does the closest perigee of the year coincide with Full Moon, but the moon will be in the “Teapot” constellation Sagittarius in approximately the same direction as our galaxy’s 4-million-mass black hole. Look toward the moon and you can imagine it there munching its way on gas clouds and stars that pass that pass too close for comfort. Given that the beast is 26,000 light years (156 quadrillion miles) from us, neither moon nor monster have any gravitational inkling of the other.

Since full phase happens early Sunday morning, the moon will appear full to the eye both Saturday and Sunday nights. I hope you’ll get to enjoy the show.

1 Response

  1. gabby mccabe

    Hi, we were looking at the full moon tonite and as we were looking at it, there were two curvy black clouds that straightened out as the moon was moving. What was that caused from? Did anyone else notice it? 6/24/2013

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