The forecast for early on November 14 indicates good viewing of the MegaMoonset over much of the US. Forecast courtesy of NOAA.
For anyone not on Medicare, November 14, 2016 presents an opportunity to view a heavenly event that has not occurred in his/her lifetime. On that date, the full moon will make its closest approach to the earth since 1948.
Full Moon, Supermoon, MegaMoon, Blue Moon
A full moon occurs every twenty-nine plus days, which means there’s one every month except for the occasional February. There can be two full moons in a month; when that happens the second full moon in a calendar month is called a ‘blue moon.’ A blue moon occurs, well, once in a blue moon, or roughly every two and a half years.
A Supermoon is a full (or, technically, new) moon which falls when the moon is within ten percent of its closest approach to the earth. Supermoons are not particularly uncommon, and there are three Super full moons in 2016: October, November, and December. But the November Supermoon is special.
A MegaMoon has no precise definition — we’re using the term to refer to something extra special about the full moon — in this case that it is closer to the earth than any full moon since 1948 (the last year the Cleveland Indians won the World Series). And it won’t be this close again until 2034. A full moon that is closer, and therefore bigger and brighter, than any other during a period of 86 years, deserves special attention.
The Path Of The Moon Around The Earth
We think of the orbits of planets and moons around their primaries as being round. But, in fact, as Johannes Kepler discovered, they are ellipses. The ellipse can be very elongated, as for example the paths of many comets, or nearly round.
The amount that an ellipse deviates from a circle is called its eccentricity. An eccentricity of zero indicates a round orbit; an eccentricity of one means the orbit is not closed and the orbiting object describes a parabola — a path that never returns. The eccentricity of the earth is .0167; the earth’s orbit is very nearly round. The eccentricity of Pluto is .2488. Pluto has a fairly un-circular orbit around the sun, and in fact crosses the orbit of Neptune from time to time. The eccentricity of Halley’s Comet is .967, a very large eccentricity, and thus Halley’s comet has a very elongated orbit, which is why we only see it every 77 years.
At perigee the moon is 14% wider and 30% brighter than at apogee. Image courtesy of NASA.
The eccentricity of the moon is .0549 — small but not insignificant. The moon’s average distance from the earth is 238,855 miles. Due to the eccentricity, the minimum and maximum distances are 225,623 and 252,088 miles.
The closest approach of the moon to the earth is called perigee; the farthest away it gets is called apogee. The moon at perigee appears 14% bigger in diameter and 30% bigger in area than the moon at apogee. Since brightness is proportional to area, the perigee full moon is 30% brighter than the apogee full moon.
Big Moon, Big Tide
Ocean tides are caused by the gravitational pull of the sun and moon. The moon’s effect is more than twice the sun’s. When they act together (new or full moon) , the tides are highest. These tides are called “spring” tides. (The word spring has nothing to do with the season; it refers to the fact the water springs forth.) At quarter moon, when the moon and sun pull in opposite directions, the tides are lowest. These are called neap tides.
With rising sea level, many coastal communities experience frequent very high tides that can cause local flooding. These have come to be known as King Tides, and regularly occur when there’s a Supermoon. With the MegaMoon, the stage is set for considerable flooding in places like Miami Beach, Florida.
The gravitational attraction of the moon and the sun are not the only factors in King Tides. Wind can blow onshore and push the water higher, or blow offshore and reduce the height of the tide. The forecast for Miami Beach for this most royal of King Tides is for a light onshore wind.
The Moon’s Orbit Is Close To The Ecliptic
The moon very likely was formed from the collision of the earth with a Mars-sized object. There is no way to tell what its orbit was after the collision. But the tug of the sun — a very large object — is powerful. The sun has pulled the moon into an orbit that deviates no more than five degrees from the ecliptic (The ecliptic is the plane of the earth’s revolution around the sun). That means that at new and full moon, the earth, the sun, and the moon are nearly lined up (three celestial objects in line is called syzygy). But only once in a great while are the three bodies lined up at the same time the moon is at perigee. That will be the case on November 14, 2016.
Bye-Bye Moon?
Due to friction, the moon is continually fighting with the earth’s tidal bulge, pulling it along. The tidal bulge is, in turn, dragging on the moon (it’s that ‘for every action, there’s an equal and opposite reaction’ thing that Newton gave us), slowing it down, and therefore pushing it into a higher orbit. But not to worry. The moon is receding from the earth at a rate of about three centimeters (less than two inches) per year — it will take a very long time for anyone to notice.
Precisely What Time Are The MegaMoon And The Full Moon?
The exact time of the MegaMoon is a matter for debate. The moon’s closest approach to Earth, lunar perigee, is 11:24 Universal time, which is 11:24 a.m. in London. On the east coast of the US, which is on Eastern Standard Time, it will be at 6:24 a.m. Subtract an hour for each time zone to the west. The moon is full, which means the sun, moon, and earth are closest to being in line exactly two and a half hours after perigee. The moon will be exceptionally big and bright for a couple of days before and after the full moon and perigee, so anytime you can view the moon from November 13 to November 16 it will be spectacular.
Weather For Viewing The MegaMoon
The moon appears to be bigger when it is near the horizon and can be compared to other objects. Photo courtesy of NASA.
In the US, the biggest moon will coincide with sunrise on November 14. However, moonrise, which is near sunset, will be just as spectacular on the 13th, 14th, and 15th. For the most pronounced visual effect, the MegaMoon should be viewed when it is near the horizon. The moon appears bigger when it is in proximity to objects to which it can be compared, though this is an optical illusion. With nothing to compare the moon to when it is high in the sky, it appears to be smaller.
Viewing conditions for the MegaMoon will be best at the following times for some metropolitan areas.
London, U.K.: London can be a gloomy place this time of year. The 14th looks like a cloudy washout, but there could be clear spots on the 13th and 15th.
New York, New York: Clear all day on the 13th and morning of the 14th, with clouds moving in thereafter.
Chicago, Illinois: Clear on the 13th, with a few clouds on the 14th and 15th.
Los Angeles, California: Mostly clear from the 13th to the 15th.
Little Bits or Dallas, Texas: Mostly clear from the 13th to the 15th.
© Copyright 2016 Jon Plotkin, All rights Reserved. Written For: Decoded Science
Jon Plotkin says
Vincent, The giant impact theory is predominant right now because the other two main theories, capture and condensation, seem to be ruled out by composition of the two bodies and physics. Granted there is also a composition problem with impact, but several low-probability solutions have been proposed. Since the moon is so much larger relative to its primary than any other moon, it must have come from a low-probability beginning.
If you have a better theory — or any plausible theory — I’d like to hear it.
Beautifully done, Jon!
It’s already huge-I took some great pictures last night! Love this informative article!
Very informative and very interesting at the same time. A much appreciated article. I’m not big on the origin of the moon bit, but it was refreshing you were not dogmatic on the popular theory. Well done.