You won't want to miss the biggest, brightest full Moon in more than 68 years. Find out what makes this supermoon so special and how best to view it.

Supermoon a Supersight

The Moon will be precisely full on Monday, November 14th at 13:52 UT, which occurs at dawn in the western half of the U.S. and Canada.
Bob King

Get ready for the Moon to hit your eye like a big pizza pie on Sunday, November 13th. That night, skywatchers around the planet will witness the closest, brightest, and biggest full Moon since January 26, 1948 — the year the Cleveland Indians last won the World Series and the 200-inch Hale telescopeon Mount Palomar was dedicated.

We'll all be crossing our fingers for clear skies, since the next such Moon won't occur until November 25, 2034. These bright, close full Moons are popularly called "supermoons," a wonderful description that makes people sit up and take notice.

The term supermoon is a recent invention. It came into common use in 2011, but appears to have been coined back in 1979 by Richard Nolle, who describes himself as a "certified, professional astrologer." His definition of a supermoon was generous: "... a new or full moon which occurs with the Moon at or near (within 90% of) its closest approach to Earth in a given orbit."

Origin of Supermoon Phenomenon

The Moon's eccentric elliptical orbit causes its distance from Earth to vary during each revolution. The nearest point is called perigee; the farthest, apogee. Not to scale.
Bob King

Because the Moon's orbit is an ellipse instead of a circle, its distance from Earth varies during the month from about 225,800 miles (363,400 km) at perigee, or closest approach, to 252,000 miles (405,550 km) at apogee. Changing the distance causes the Moon's size and brightness to change as well. A perigee or supermoon is on average 7% bigger and 16% brighter than an average full Moon, but during an unusually close perigee, the full Moon can be 12–14% larger than a full Moon at apogee (sometimes called a micromoon) and 30% brighter.

Perigee and Apogee Moon

A comparison of the Moon at its closest to Earth (left) and farthest. The change in distance makes the full Moon look 14% larger at perigee than apogee. 
Laurent Laveder

Since we can only see one Moon in the sky, there's no way to directly compare macro and micro full Moons in real time, so you'll have to recall the appearance a typical full Moon and compare it to the upcoming supermoon. Or hold the image of November's supermoon in your mind's eye and compare it to the next micromoon on June 8, 2017.

How about a measuring device? Consider making what I'll call a Supermoon Sighter. With a pair of scissors, cut a series a slots of varying widths in an index card, then hold the card as best you can parallel to your face and at maximum arm length while facing the Moon. Close one eye and use the other to determine the slot into which the Moon fits snugly. Mark the date under that slot and its width in millimeters.

Supermoon Sighter

Make a simple Moon-measuring device by cutting slots of different widths in an index card. It's not hard science but will serve to measure larger differences in lunar diameter with the naked eye. 
Bob King

Follow exactly the same procedure during an apogee Moon and you should be able to see the size difference. It works best when the Moon is visible in twilight because the brighter sky background makes the slots easier to see. Of course, you can simply take photos of November's and next June's full Moons using the same telephoto or telescope settings and place them side-by-side as Laurent Laveder did in the photo above.

Several times each year, the full Moon occurs within a day or two of perigee, making supermoons somewhat common ... though not equal. The closer perigee and the moment of full Moon are to coinciding, the more exceptional the supermoon. Not only will November's full Moon occur at the closest perigee of the year, but the "stretchiness" of the lunar orbit will bring it in even closer.

Supermoons Past, Present, and Future

These panels show the sky to the east at nightfall on the dates of the last, current, and future supermoons. Even though the Moon will be closest on November 14th, it's depicted on the 13th (center panel), when most North American observers will be out watching. The 1948 event found the Moon in the company of Mars and Saturn. During the next, the Moon will occult numerous Hyades star cluster stars and Aldebaran. Lunar distances are measured from the center of Earth to the center of the Moon.
Maps: Bob King, Source: Stellarium

Sometimes the Moon's orbit is rounder, other times more elliptical, due to the ever-changing distances and relative positions of the Sun, Moon, and Earth, the inclination of the Moon's orbit, the non-spherical shape of the Earth, and even the gravitational attraction of the other planets. But the Sun's the biggest culprit — its gravitational attraction is more than twice as large as that between Moon and Earth. Add all these effects together, and the Moon's eccentricity (the amount by which the orbit deviates from a circle) varies from 0.026 to 0.077, or 5.5%. A circle has an eccentricity of 0.0.

When more oval, the Moon's perigee point gets unusually close to Earth, and if a full Moon arrives at that point, it will be considerably closer to us than during those times when the lunar orbit more closely resembles a circle. In a word, the Moon's perigee distance varies. Apogee too, naturally!

Location, Location, Location

If a new or full Moon lies at the apogee or perigee point, the shape of the Moon's orbit can be slightly altered, resulting in a closer perigee than normal and an exceptional supermoon. A full Moon that occurs at the closest perigee of the year is said to be at proxigee. Not to scale.
Bob King

Perigee and apogee distances also vary if a new or full Moon occurs at either point. Then all three bodies — Earth, Moon, and Sun — are in a straight line and exert their greatest gravitational attraction on one another. Earth and Sun in effect tug the Moon a little bit closer yet. And if this alignment happens within a few months of the Earth being closest to the Sun, when the Moon feels the Sun's gravity strongest, our satellite can snug up even closer to us. And wouldn't you know, we're closest to our star from November through February.

All these conditions will be met on November 13-14 to make this month's supermoon the most amazing until 2034. To enhance your supermoon experience, I encourage you to catch the Moon at moonrise, when the Moon Illusion will be at work. This psychological trick our eyes and brain play on us makes the Moon appear much larger when viewed near the horizon than higher overhead. Click here to find out exactly when the Moon will rise for your location.

Share a Unique Lunar Moment

Share November's supermoon with friends and family. The Moon will make its grandest impression at moonrise November 13th and before moonset the following morning for the Americas. Click the image to find out when the Moon rises for your town.
Göran Strand / astrofotografen.se

For much North America, the supermoon will be closest and brightest during the overnight hours of November 13–14 — Sunday night and Monday morning until moonset. The moment of maximum supermoonness occurs at 11:23 UT (6:23 a.m. EST) Monday morning, November 14th, so everyone across the Americas will have the chance to see the Moon when it's at its closest, although it will be minutes before setting if you live on the East Coast. At that time, the distance between Earth and Moon will shrink to a mere 221,524 miles (356,509 km) or 1.2 light-seconds. Compare this to the average distance of 238,900 miles (384,472 km), a tenth of a light-second farther off.

Bear in mind, that the Moon's closest approach to Earth occurs 2½ hours before it's technically full, so observers in the Eastern states will see an ever-so-slightly-less-than-full Moon. Those living in the western half of the U.S., including Alaska and Hawaii, will get to experience both the "special moment" and the Moon at maximum fullness in either a twilight or dark sky. In the eastern hemisphere, including Europe and Africa, the Moon will be a little closer on the evening of Monday November 14th. Times are included below so you can explore your inner lunatic:

Moon closest to Earth on November 14th at 11:23 UT (Greenwich Time) or Monday morning November 14th at:

  • 6:23 a.m. Eastern Standard Time
  • 5:23 a.m. Central
  • 4:23 a.m. Mountain
  • 3:23 a.m. Pacific
  • 2:23 a.m. Alaska
  • 1:23 a.m. Hawaii

Moment of maximum full Moon occurs on November 14th at 13:52 UT or Monday morning November 14th at:

  • 8:52 a.m. Eastern
  • 7:52 a.m. Central
  • 6:52 a.m. Mountain
  • 5:52 a.m. Pacific
  • 4:42 a.m. Alaska
  • 3:32 a.m. Hawaii
Where It's Always Clear

Cloudy skies on the big night? Click over to the Virtual Telescope Project for a live view.
Gianluca Masi

If the weather's bad from your town on both the 13th and 14th, you can fall back on the Web. Italian astronomer Gianluca Masi will live stream the joy of the giant Moon on his Virtual Telescope Project starting at 16:00 UT (11 a.m. Eastern) November 14th. You can also watch it live on Slooh's website where they're calling it the Mega Beaver Moon. 'Beaver' refers to the November moon's traditional name. In November, the early colonists and Algonquin tribes set beaver traps before the swamps froze to ensure a good supply of warm furs for the coming winter.

Tides are always higher at new and full Moons due to the alignment of Sun, Earth, and Moon, but an extra-close Moon will also mean higher tides than normal. If you live along a coast line, watch for these on November 14th and several days after.

Quite wonderful, isn't it, that so many small gravitational influences can add up to produce such a singular event. It makes us feel connected to the cosmos in a very real way. Clear skies!