By now, you’ve heard the news. We’ll spare you the “it’s a bird, it’s a plane…” routine to usher in the Supermoon 2016. This month’s Full Moon is not only the closest for the year, but the nearest Full Moon for a 80 year plus span.
Like Blue and Black Moons, a Supermoon is more of a cultural phenomenon than a true astronomical event. The Moon’s orbit is elliptical, taking it from 362,600 to 405,400 km from the Earth in the course of its 27.55 day anomalistic orbit from one perigee to the next. For the purposes of this week’s discussion, we consider a Supermoon as when the Full Moon occurs within 24 hours of perigee, and a Minimoon as when the Full Moon occurs within 24 hours of apogee. From the Earth, the Moon varies in apparent size from 29.3” to 34.1” across. This month, the Moon reaches perigee on November 14th at 356,511 kilometers distant, 2 hours and 22 minutes before Full.
This is the closest perigee Moon for 2016, beating out the April 7th, 2016 perigee Moon by just 652 kilometers. Perigee can vary over a span of 2,800 kilometers. In the 21st century, the farthest lunar perigee (think the ‘most distant near point’) occurs on January 3rd, 2100 at 370,356 kilometers distant, while the closest perigee of the century (356,425 kilometers) occurs on December 6th , 2052.
When the Moon reaches Full on November 14th at 13:51 UT, it’s just 356,520 kilometers distant, (that is , as measured from the Earth’s center) the closest Full Moon since January 26th, 1948 (356,490 km) and until November 25th , 2034 (356,446 km) losing out to either dates by just 21 kilometers.
Why does perigee vary? Well, as the Moon orbits the Earth, the Sun tugs our large natural satellite’s orbit around as well, in an 8.85 year cycle known as the precession of the line of apsides. Earth’s orbit is elliptical as well, and the tugging of the Sun (and to a much lesser degree, the other planets in the solar system) alters the perigee and apogee points slightly based on where the Earth-Moon pair fall in their swing about a common barycenter.
The November Full Moon is also known as the Full Beaver Moon by the Algonquin Native Americans, a good time to ensure a supply of winter furs before the swamps froze over. A good sign that even in 2016, ‘Winter is Coming.’
Does the Moon look any larger to you than usual as it rises to the east opposite to the setting Sun on Monday night? When the Moon reaches Full, it passes the zenith as seen from the central Indian Ocean region just south of Sri Lanka, 354,416 km distant. Of course, as the Moon rises, it’s actually one full Earth radii more distant than when straight overhead at the zenith.
Would you notice any difference in the size of the November Full Moon, if you didn’t know better? The 4′ odd difference between an apogee and perigee Full Moon is certainly discernible in side-by-side images… but it’s interesting to note that early cultures did not uncover the elliptical nature of the Moon’s motion, though it certainly would have been possible. Crystalline spheres ruled the day, a sort of perfection that was just tough to break in the minds of many.
Be sure to enjoy the rising Full Moon on Monday night, the largest for many years to come.
Ready for some lunar action of proxigean proportions? This weekend’s Full Moon ushers in that most (infamous?) of internet ready cultural memes: that of the Supermoon. This moniker stands above the Blood, Mini, and Full Moons both Black and Blue as the Full Moon of the year that folks can’t seem to get enough of, and astronomers love to hate.
But wait a minute: is this weekend’s Full Moon really the closest of the year?
Nope, though it’s close. But this month’s Full Moon does, however, usher in what we like to call Supermoon season.
Let us explain.
First, we’ll let you in on the Supermoon’s not so secret history. Yes, the meme arose over the last few decades, mostly due to the dastardly deeds of astrologers. Y’know, that well meaning friend/coworker/relative/anonymous person on Twitter that constantly mistakes your passion for the night sky as ‘astrology.’ Anyhow, the idea of the Supermoon has gained new life via the internet, and loosely translates as the closest Full Moon of the year. Sometimes, its dressed up with the slightly science-y sounding ‘a Full Moon along the closest 90% of its orbit’ (!) definition.
Now, to know the orbit of the Moon is to understand celestial mechanics. The Moon’s orbit is indeed elliptical, ranging from an average perigee (its closest point to the Earth) of 362,600 kilometers, to an apogee of 405,400 kilometers distant.
Fun fact: the time it takes the Moon to go from one perigee to the next (27.55 days) is one anomalistic month, a fine pedantic point to bring up to said relative/coworker the next time they refer to you as an astrologer.
And yes, the perigee Full Moon is a thing. We even like to throw about the quixotic term of the proxigean Moon, a time when tidal variations are at an extreme. Plus, all perigees are not created equal, but range from 356,400 kilometers to 370,400 kilometers distant, as the Earth-Moon system not only swings around its common barycenter, but the Sun also drags the entire orbit of the Moon around the Earth, completing one complete revolution every 8.85 years in what’s known as the precession of the line of apsides. Note that the nodes of the Moon’s orbit actually move in the opposite direction, with an 18.6 year period.
Yup, the motion of the Moon has given humanity a fine study in Celestial Mechanics 101. Anyhow, we contend that a more succinct definition for a perigee ‘Supermoon’ is simply a Full Moon that falls within 24 hours of perigee. Under this definition, the Full Moon this Sunday on October 16th occurring at 4:23 Universal Time (UT) certainly meets the criterion, occurring 19 hours and 24 minutes before perigee… as does the Full Moon of November 14th (2.4 hours from perigee) and December 13th (just under 24 hours from perigee).
For extra fun, said November 14th perigee Full Moon is the closest in 30 years; expect Supermoon lunacy to ensue.
A fun place to play with Full and New Moons vs perigee and apogee past present and future is Fourmilab’s Lunar Apogee and Perigee Calculator. Hey, it’s what we do for fun. Looking over these cycles, you’ll notice a pattern of ‘supermoon seasons’ emerge, which moves forward along the calendar about a lunation a year. (that’s our friend the precession of the line of apsides at work again).
(another fun fact: the time it takes for the Moon to return to a similar phase—for example, Full back to Full—is 29.5 days, and known as a synodic month.)
The Full Moon does appear slightly larger at perigee than apogee, to the tune of 29.3′ versus 34.1′ across. This change is enough to notice with the unaided eye, though the Moon is deceptively smaller than it appears: you could, for example, line up 654 ‘Supermoons’ around the local horizon from end to end.
The October Moon is also referred to by the Algonquin Native Americans as the ‘Hunter’s Moon,’ a time to use that extra illumination to track down vital sustenance as the harsh winter approaches. Very occasionally, the Harvest Full Moon falling near the September southward equinox falls in early October (as occurs next year in 2017) and bumps the Hunter’s Moon from its monthly slot.
Be sure to stalk the rising Hunter’s Moon near perigee this weekend. Of course, we’ll be shooting at our prey with nothing more than a camera, as the Full Moon rises from behind the Andalusian foothills.
Wow! The astrophotographers out there are getting artsy! Take a look at some of the most artistic images of the full Moon we’ve seen yet.
The August 10 full Moon was a so-called “super” Moon — and it was the “super-est” of a trio of full Moons being at perigee, or its closest approach to the Earth in its orbit. It was just 356,896 kilometers distant at 17:44 UTC, less than an hour from Full. You can see a comparison shot of the perigee and apogee Moons this year immediately below. Find all the technical details here, but enjoy a gallery of great images from around the world
It was prom night in Cairns… so the fancy cars were out. See Joseph’s other “prom supermoon” image here.
Even NASA got into the “super Moon” astrophoto craze. NASA photographer Bill Ingalls took this beautiful image at The Peace Monument on the grounds of the United States Capitol, in Washington D.C. :
Want to get your astrophoto featured on Universe Today? Join our Flickr group or send us your images by email (this means you’re giving us permission to post them). Please explain what’s in the picture, when you took it, the equipment you used, etc.
‘Tis the season once again, when rogue Full Moons nearing perigee seem roam the summer skies to the breathless exhortations of many an astronomical neophyte at will. We know… by now, you’d think that there’d be nothing new under the Sun (or in this case, the Moon) to write about the closest Full Moons of the year.
But love ‘em or hate ‘em, tales of the “Supermoon” will soon be gracing ye ole internet again, with hyperbole that’s usually reserved for comets, meteor showers, and celeb debauchery, all promising the “biggest Full Moon EVER…” just like last year, and the year be for that, and the year before that…
How did this come to be?
What’s happening this summer: First, here’s the lowdown on what’s coming up. The closest Full Moon of 2014 occurs next month on August 10th at 18:11 Universal Time (UT) or 1:44 PM EDT. On that date, the Moon reaches perigee or its closest approach to the Earth at 356,896 kilometres distant at 17:44, less than an hour from Full. Of course, the Moon reaches perigee nearly as close once everyanomalistic month (the time from perigee-to-perigee) of 27.55 days and passes Full phase once every synodic period (the period from like phase to phase) with a long term average of 29.53 days.
And the August perigee of the Moon only beats out the January 1st, 2014 perigee out by a scant 25 kilometres for the title of the closest perigee of the year, although the Moon was at New phase on that date, with lots less fanfare and hoopla for that one. Perigee itself can vary from 356,400 to 370,400 kilometres distant.
But there’s more. If you consider a “Supermoon” as a Full Moon falling within 24 hours of perigee, (folks like to play fast and loose with the informal definitions when the Supermoon rolls around, as you’ll see) then we actually have a trio of Supermoons on tap for 2014, with one this week on July 12th and September 9th as well.
What, then, is this lunacy?
Well, as many an informative and helpful commenter from previous years has mentioned, the term Supermoon was actually coined by an astrologer. Yes, I know… the same precession-denialists that gave us such eyebrow raising terms as “occultation,” “trine” and the like. Don’t get us started. The term “Supermoon” is a more modern pop culture creation that first appeared in a 1979 astrology publication, and the name stuck. A more accurate astronomical term for a “Supermoon” is a perigee-syzygy Full Moon or Proxigean Moon, but those just don’t seem to be able to “fill the seats” when it comes to internet hype.
One of the more arcane aspects set forth by the 1979 definition of a Supermoon is its curiously indistinct description as a “Full Moon which occurs with the Moon at or near (within 90% of) its closest approach to Earth in a given orbit.” This is a strange demarcation, as it’s pretty vague as to the span of distance (perigee varies, due to the drag of the Sun on the Moon’s orbit in what’s known as the precession of the line of apsides) and time. The Moon and all celestial bodies move faster near perigee than apogee as per Kepler’s 2nd Law of planetary motion.
We very much prefer to think of a Proxigean Moon as defined by a “Full Moon within 24 hours of perigee”. There. Simple. Done.
And let’s not forget, Full phase is but an instant in time when the Moon passes an ecliptic longitude of 180 degrees opposite from the Sun. The Moon actually never reaches 100% illumination due to its 5.1 degree tilt to the ecliptic, as when it does fall exactly opposite to the Sun it also passes into the Earth’s shadow for a total lunar eclipse.
-Check out this animation of the changing size of the Moon and its tilt — known as libration and nutation, respectively — as seen from our Earthly perspective over the span of one lunation.
The truth is, the Moon does vary from 356,400 to 406,700 kilometres in its wonderfully complicated orbit about our fair world, and a discerning eye can tell the difference in its size from one lunation to the next. This means the apparent size of the Moon can vary from 29.3’ to 34.1’ — a difference of almost 5’ — from perigee to apogee. And that’s not taking into account the rising “Moon illusion,” which is actually a variation of an optical effect known as the Ponzo Illusion. And besides, the Moon is actually more distant when its on the local horizon than overhead, to the tune of about one Earth radius.
Like its bizarro cousin the “minimoon” and the Blue Moon (not the beer), the Supermoon will probably now forever be part of the informal astronomical lexicon. And just like recent years before 2014, astronomers will soon receive gushing platitudes during next month’s Full Moon from friends/relatives/random people on Twitter about how this was “the biggest Full Moon ever!!!”
Does the summer trio of Full Moons look bigger to you than any other time of year? It will be tough to tell the difference visually over the next three Full Moons. Perhaps a capture of the July, August and September Full Moons might just tease out the very slight difference between the three.
And for those preferring not to buy in to the annual Supermoon hype, the names for the July, August and September Full Moons are the Buck, Sturgeon and Corn Moon, respectively. And of course, the September Full Moon near the Equinox is also popularly known as the Harvest Moon.
And in case you’re wondering, or just looking to mark your calendar for the next annual “largest Full Moon(s) of all time,” here’s our nifty table of Supermoons through 2020, as reckoned by our handy definition of a Full Moon falling within 24 hours of perigee.
So what do you say? Let ‘em come for the hype, and stay for the science. Let’s take back the Supermoon.
OK, it’s a bad gag, I know. But the movie Man of Steel isn’t the only thing that’s “super” about June this year. The closest full Moon of 2013 occurs on June 23, when it will be 356,991 kilometres from Earth, within 600 kilometres of its closest possible approach. When the Moon is closest to Earth in its orbit, it also appears just a bit larger in the sky. But that’s if you’re really paying attention, however!
Some claims circulating on the Internet tend to exaggerate how large the Moon will actually appear. And as for the assertions that the Moon will look bright purple or blue on June 23, that’s just not true. As seems to happen every year, the term “supermoon” has once again reared its (ugly?) head across ye ole Internet. Hey, it’s a teachable moment, a good time to look at where the term came from, and examine the wonderful and wacky motion of our Moon.
I’ll let you in on a small secret. Most astronomers, both of the professional and backyard variety, dislike the informal term “supermoon”. It arose in astrology circles over the past few decades, and like the term “Blue Moon” seems to have found new life on the Internet. A better term from the annuals of astronomy for the near-coincidence of the closest approach of the Full Moon would be Perigee Full Moon. And if you really want to be archaic, Proxigean Moon is also acceptable.
On June 23, 2013, the Moon will be full at 7:32 AM EDT/ 11:32 UT, only 20 minutes after it reaches perigee, or its closest point to Earth in its orbit.
You can see the change in apparent size of the Moon (along with a rocking motion of the Moon known as nutation and libration) in this video from the Goddard Space Flight Center’s Scientific Visualization Studio. You can also see full animations for Moon phases and libration for 2013 from the northern hemisphere and southern hemisphere.
And all perigees are not created equal, either. Remember, a Full Moon is an instant in time when the Moon’s longitude along the ecliptic is equal to 180 degrees. Thus, the Full Moon rises (unless you’re reading this from high polar latitudes!) opposite as the Sun sets. Perigee also oscillates over a value of just over 2 Earth radii (14,000 km) from 356,400 to 370,400 km. And while that seems like a lot, remember that the average distance to the Moon is about 60 earth radii, or 385,000 km distant.
Astronomers yearn for kryptonite for the supermoon. The Moon passes nearly as close every 27.55 days, which is the time that it takes to go from one perigee to another, known as an anomalistic month. This is not quite two days shorter than the more familiar synodic month of 29.53 days, the amount of time it takes the Moon to return to similar phase (i.e. New to New, Full to Full, etc).
This offset may not sound like much, but 2 days can add up. Thus, in six months time, we’ll have perigee near New phase and the smallest apogee Full Moon of the year, falling in 2013 on December 19th. Think of the synodic and anomalistic periods like a set of interlocking waves, cycling and syncing every 6-7 months.
You can even see this effect looking a table of supermoons for the next decade;
Super Moons for the Remainder of the Decade 2013-2020.
Note that the supermoon slowly slides through our modern Gregorian calendar by roughly a month a year.
In fact, the line of apsides (an imaginary line drawn bisecting the Moon’s orbit from perigee to apogee) completes one revolution every 8.85 years. Thus, in 2022, the supermoon will once again occur in the June-July timeframe.
To understand why this is, we have to look at another unique feature of the Moon’s orbit. Unlike most satellites, the Moon’s orbit isn’t fixed in relation to its primaries’ (in this case the Earth’s) equator. Earth rotational pole is tilted 23.4 degrees in relation to the plane of its orbit (known as the ecliptic), and the Moon’s orbit is set at an inclination of 5.1 degrees relative to the ecliptic. In this sense, the Earth-Moon system behaves like a binary planet, revolving around a fixed barycenter.
The two points where the Moon’s path intersects the ecliptic are known as the ascending and descending nodes. These move around the ecliptic as well, lining up (known as a syzygy) during two seasons a year to cause lunar and solar eclipses.
But our friend the line of apsides is being dragged backwards relative to the motion of the nodes, largely by the influence of our Sun. Not only does this cause the supermoons to shift through the calendar, but the Moon can also ride ‘high’ with a declination of around +/-28 degrees relative to the celestial equator once every 19 years, as happened in 2006 and will occur again in 2025.
Falling only two days after the solstice, this month’s supermoon is also near where the Sun will be in December and thus will also be the most southerly Full Moon of 2013. Visually, the Full Moon only varies 14% in apparent diameter from 34.1’ (perigee) to 29.3’ (apogee).
A fun experiment is to photograph the perigee Moon this month and then take an image with the same setup six months later when the Full Moon is near apogee. Another feat of visual athletics would be to attempt to visually judge the Full Moons throughout a given year. Which one do you think is largest & smallest? Can you discern the difference with the naked eye? Of course, you’d also have to somehow manage to insulate yourself from all the supermoon hype!
Many folks also fall prey to the rising “Moon Illusion.” The Moon isn’t visually any bigger on the horizon than overhead. In fact, you’re about one Earth radii closer to the Moon when it’s at the zenith than on the horizon. This phenomenon is a psychological variant of the Ponzo illusion.
Here are some of the things that even a supermoon can’t do, but we’ve actually heard claims for:
– Be physically larger. You’re just seeing the regular-sized Moon, a tiny bit closer.
– Cause Earthquakes. Yes, we can expect higher-than-normal Proxigean ocean tides, and there are measurable land tides that are influenced by the Moon, but no discernible link between the Moon and earthquakes exists. And yes, we know of the 2003 Taiwanese study that suggested a weak statistical correlation. And predicting an Earthquake after it has occurred, (as happened after the 2011 New Zealand quake) isn’t really forecasting, but a skeptical fallacy known as retrofitting.
– Influence human behavior. Well, maybe the 2013 Full Moon will make some deep sky imagers pack it in on Sunday night. Lunar lore is full of such anecdotes as more babies are born on Full Moon nights, crime increases, etc. This is an example the gambler’s fallacy, a matter of counting the hits but not the misses. There’s even an old wives tale that pregnancy can be induced by sleeping in the light of a Full Moon. Yes, we too can think of more likely explanations…
– Spark a zombie apocalypse. Any would-be zombies sighted (Rob Zombie included) during the supermoon are merely coincidental.
Do get out and enjoy the extra illumination provided by this and any other Full Moon, super or otherwise. Also, be thankful that we’ve got a large nearby satellite to give our species a great lesson in celestial mechanics 101!