What Is A Supermoon?

What is a supermoon? Is it a myth is mostly motivated by desire for publicity or is it true astronomical phenomenon?

Beware the continuing media hype about supermoons. The upcoming supermoon, technically occurring at 7:32 a.m. (EDT) this Sunday in North America, will no doubt have some in a tizzy, so here are the facts.

What Is A Supermoon?

The term “supermoon” was first coined by astrologer Richard Nolle to describe the full or new Moon when it's less than 223,000 miles (359,000 km) from Earth. That’s about 6% closer than the average Earth-Moon distance, which is 239,000 miles.

Despite being closer than usual, supermoons are rather ordinary and, by Nolle’s definition, take place several times a year. But the media won’t hype that up — can you imagine headlines publicizing “Come out and see the Moon that's a little bigger than normal!” or “Look out for this amazing event that happens several times a year!” — yeah, me neither.

Fact vs. Fiction

What is a supermoon? Illustration
The diameter of the full Moon at perigee (closest approach to Earth) as compared to apogee.
NASA
Over the next few days, you might hear startling statistics about size and brightness increases this weekend, but don’t be fooled. This supermoon will only be about 7% larger than the average full moon. Most sources advertise a 14% size increase because they're comparing it with the smallest full moon of the year.

This weekend's supermoon will also bring the largest tides of 2013, because a closer Moon exerts a stronger gravitational pull, creating more variation between the tides. However, this variation is hardly enough to account for massive earthquakes, flooding, or volcanic eruptions.

The Moon Illusion

But even though the Moon isn't noticeably bigger on the night of the supermoon, at least not without some kind measuring tool, lots of folks will head out to see a huge full Moon looming over the treetops. The so-called Moon Illusion causes the Moon to appear bigger when viewed along the horizon and can fool people into believing the supermoon myth.

Nobody quite understands why the Moon illusion happens, but here are two of the theories psychologists think might explain this effect.

Ponzo Optical Illusion
The image demonstrates the Ponzo Illusion, an optical illusion that explains why the Moon appears larger near the horizon.
Charles Stangor's Introduction to Psychology
One theory claims that our brain perceives the distance to the sky directly overhead as closer than the distance to the horizon. We think the Moon must be bigger along the horizon because we perceive the distance to the horizon as farther away. Don't buy the theory? Look at the picture to the right. The top line seems larger than the bottom one. But measure for yourself and, surprisingly, you'll find the lines are the same size.

The Ebbinghaus Illusion says that we perceive an object's size based on the relative size of its surroundings. The two orange circles in this image are identical in size, yet the circle on the right appears larger because it is surrounded by smaller circles.
New World Encyclopedia
Psychologists have also suggested that an overhead Moon looks smaller because it’s surrounded by empty space, while a Moon near the horizon appears larger juxtaposed against trees and buildings. The picture on the right shows two orange circles of identical size. But the orange circle on the right appears larger than the one at the left because of its relative size to the surrounding circles.

So the supermoon might look bigger than normal if you see it in the evening when the Moon's just rising, but the real size difference isn't big enough to notice.

Then what is there to look forward to? As always, a full Moon is a great opportunity for astrophotography — it’s so bright that you only need exposures of a fraction of a second, just like daylight photos. The supermoon technically happens at 7:32 a.m. (EDT) on Sunday morning, but the Moon will shine just about as full and bright at sunset on Saturday as it will at sunset on Sunday.

And despite the fact that the supermoon isn't as extraordinary as some might have you think, any full Moon is still a spectacular sight to behold.

33 thoughts on “What Is A Supermoon?

  1. Pete Jackson

    It would be interesting to compare how much detail one can see on the Moon when it is near perigee than when it is near apogee.

    One might say 7 percent larger or smaller in size wouldn’t matter, but it does! I am old enough to remember when the diagonal measure of a television screen was a very big feature in advertising. A 17-inch TV was considered so small, compared to the latest 21-inch screen. And so it was, people really thought that they could see much more on the larger screen.

    Well, if we consider a 19-inch screen as average, then the Moon at apogee would be like watching on a 17.7 inch screen, and the Moon at perigee would be like watching on a 20.3 inch screen. The 20.3 inch screen would certainly show more than the 17.7 inch screen.

  2. rocksnstarsTom Hoffelder

    Thank you Ms. Balouchi. Thank you thank you thank you! I’ve been trying to say this for years! And comparing the moon (naked eye) to a 19 inch TV may be an apples vs oranges thing. The fact that the moon is only around a 1/2 degree in diameter has to be considered. The angle subtended by a 19 inch TV of course depends on how close you are to it, but chances are it is considerably more than 1/2 degree. My guess is that if you sat far enough away from the large and small TVs to make them the same size as the moon at apogee and perigee, you’d have a hard time seeing much difference in the image. This would especially be true if you didn’t have the two side by side to compare, which is of course the case with slightly different sized moons.

  3. Frank Reed

    Pete Jackson asked about "detail" when the Moon is closer. Of course, there is a slight increase in the amount of detail you can see. The human eye under good conditions has a resolution of one minute of arc. That’s what "20:20" vision is actually defined to be. Under excellent conditions, those with excellent vision can sometimes resolve angles as small as 0.7 minutes of arc. But let’s stick with 1.0 minutes since that applies to most people with good (or corrected vision). This scale represents the "pixels" of human vision. So how many pixels are there across the Moon? The Moon at mean distance has a diameter of 31.1 minutes of arc –therefore 31 visual "pixels". The Moon at perigee this weekend has a diameter of 33.4 minutes –therefore 33 visual "pixels". So yes, you can see a little more detail when the Moon is at perigee: two more pixels. And you can try this out observationally. Draw the Full Moon without optical aid carefully plotting the dark maria and the bright ejecta blankets of craters. It’s great naked eye astronomy. Try it this month, and then try again in six months. You’ll see more variation from the lunar librations than from any increase in apparent detail visible: 33 pixels versus 31 pixels just isn’t a bit difference. …by the way, you could compare the squares of those two numbers if you want to count areal pixels (and multiply by pi/4). But that’s just a different way of saying the same thing.

  4. Frank Reed

    In fact, the Moon near the horizon on any given day is SMALLER than when higher in the sky if you actually measure it (e.g. with a sextant). It’s smaller in the vertical dimension due to refractional flattening (makes the Moon look a bit oval when it’s low in the sky) and it’s smaller because it’s literally further away by up to nearly 4000 miles (this is called the "augmentation" in celestial navigation). These are both real, measurable effects. They’re small, totalling less than a minute of arc in most cases, but it makes the Moon illusion even more remarkable. The Moon is LITERALLY smaller than normal when low in the sky, despite the compelling perceptual illusion. This peculiar contradiction has been discussed for centuries, and I recently wrote up a post on the "NavList" message boards quoting a discussion of the Moon illusion from 1809 by Andrew Mackay. More here: http://fer3.com/arc/m2.aspx/Perigee-Full-Moon-g24415

  5. Frank Reed

    The article mentions the astrologer who coined this word. He doesn’t own it, of course, and we in astronomy could simply adopt it as a name for the closest "Perigee Full Moon" in a cycle. Much the same way that the un-necessary term "blue moon" is now applied to the second Full Moon in a month. Casual observers like pointing at the Moon and sticking a label on it. But that astrologer who coined the term has a whole complex theory of Moon disasters (nonsense, of course) connected to it, and indeed that’s how this "Supermoon" entered the English language with such a bang in March 2011. He "predicted" the devastating earthquake in Japan (and the Wikipedia page on "Supermoon" was born within 24 hours). Of course any crank theory that repeats its predictions for thirty years will eventually get a hit. Major earthquakes show no connection with Perigee Full Moons historically. The astrologer does at least inform us of his source –he was inspired by Fergus Wood and his eccentric tome on "The Strategic Role of Perigean Spring Tides" published c.1976. Ironically, this is the exact same author and source which inspired Donald Olson et al. to create their ridiculous theory, published last year by S&T, claiming that Perigee Spring Tides in January 1912 might have freed icebergs from the Canadian coast eventually dooming the Titanic (displaying a shocking ignorance of actual tidal dyanmics). That gives us two silly "Perigee Full Moon" theories in the past two years, both inspired by one bizarre semi-science book.

  6. G P Hanner

    Quite a few decades ago, when I was a USAF navigator, I witnessed a combination of lunar events that was literally awesome.

    We had departed Guam, bound for Honolulu, an hour or so before sunset on Guam. Well before we got to Wake Island the sun had set and the eastern sky was beginning to take on a reddish glow. The pilots asked me what the light was out there on the horizon; it told them it was the moon. A few minutes later the copilot again asked me if I was sure that was the moon; I told him yes. And then I checked the air almanac to make sure; it was the moon. The copilot was becoming increasingly concerned about what was out in front of us so I went forward and looked for myself. It was an amazing sight.

    The rising moon seemed to take up a third of the horizon – and it was a ruddy color. Since we were flying at around 480 knots the moon rise was coming faster than normal and this great ruddy moon seemed to fill the sky. Finally it rose fully and the illusion vanished. On reflection, I realized that we had seen a full moon in eclipse as it was rising and that accounted for the ruddy color we had seen.

    It was a memorable sight.

  7. rocksnstarsTom Hoffelder

    In case you want to do my test with the different size TVs, 19 inches measures 1/2 degree if you are 180 feet away from the TV. Not many living rooms that big! (I think I remember how to do trig calculations…)

    Most of the media articles are strictly about looking at the supersilly moon without a telescope, which makes sense, since there isn’t much reason to look at a full moon with a telescope due to the lack of contrasting shadows.

  8. Milan

    … why there are not more people at star parties?

    The explanation of the Moon Illusion is excellent, thank you. But making fun of the "myth of supermoon" is a classic soulless approach of academic scientists who do astronomy by mouse click and never bother to look at the sky!

    Why destroy the curiosity and mystique that the general public has? Why not instead use this "hype" to invite them to the public observatories and star parties, let them look at the Moon (and the rest) and explain what is going on? After all, these "6%" and "14%" do have a meaning.

    If we understand something does this mean that it is no longer interesting to us? (What would Dick Feynman think about that?) And even if that is the case, it is still interesting to someone else.

  9. Pete Jackson

    But now we can use smartphones, so we need only to bring up a web page or image of the full Moon on our phone, and examine it from distances of 16.7 feet and 19.3 feet to compare the apparent sizes of the Moon at apogee and perigee. This can be done in most residences, I would suspect.

    Actually, my motivation in bringing up the references to 17 inch and 21 inch televisions was to bring in the irony of how the advertising in the 50s made a big deal about relatively small differences in TV screen size.

  10. Frank Reed

    No trig needed! For small angular sizes (less than a few degrees), you shouldn’t be tapping the trig keys on your calculator. Angles are ratios. The angular size of anything is its size across the line of sight (height of a building, width of a tv screen, diameter of a moon) divided by the distance to it. The result is a pure ratio or an angle "in radians". And then to convert to minutes of arc, you multiply by 3438. Nice because you can do all that to reasonable accuracy in your head. No calculator required as long as you can remember 3438 (or equivalent –it’s just 180*60/pi).

  11. Virginia

    Thanks, Milan for pointing out the importance of astronomical events that have the potential to get non-astronomers to go out and look at the night sky.

    It’s nice for scientists to feel superior while saying there’s nothing particularly special about this Full Moon, but it’s not terribly inspiring, is it?

    If astronomers don’t take advantage of any and every opportunity to get people to go out at night and look up, how do they expect to interest those same people in the problem of light pollution, for example?

  12. Bob Sills

    I wish this idiotic hype about the supermoon would disappear from the news media.

    People’s expectations are raised, and they expect a fantastically big and bright full moon. In reality, an ordinary observer can’t tell the difference between one full moon and another.

    People should enjoy the beauty of the night sky in its many forms, including the spectacle of a full moon hanging over the horizon; but supermoon hype is dishonest and misleading.

  13. Matthias Dopleb

    I have compared the perigee full moon of June 2013 with two extremes – both in terms of moon’s distance/closeness and brightness (simulated with GUIDE 9):

    23 June 2013, 11:32 UT
    mag -12.8
    geocentric distance: 356,991 km
    99.90% illuminated
    Phase angle: 3.70 degrees
    Elongation from Sun 176.29 degrees
    angular diameter: 33.46 arcminutes

    Especially close full moon
    19 October 2338 BC (Gregorian calendar), 10:41 UT
    mag -12.8
    geocentric distance: 356,341 km
    99.81% illuminated
    Phase angle: 5.02 degrees
    Elongation from Sun: 174.97 degrees
    angular diameter: 33.52 arcminutes
    seen from zenith: 34.13 arcminutes (34′ 8.7")

    Especially bright full moon
    1 February 2762, 6:23 UT (just after a lunar eclipse)
    mag -12.9 (extremely bright due to small phase angle!)
    geocentric distance: 356,572 km
    99.98% illuminated
    Phase angle: 1.57 degrees
    Elongation from Sun: 178.42 degrees
    angular diameter: 33.50 arcminutes

  14. Peter WilsonPeter

    “One theory claims that our brain perceives the distance to the sky directly overhead as closer than the distance to the horizon.” That is correct. The “picture at right” has nothing to do with it, however. Our brains model the sky as an up-side-down salad bowl, not a hemisphere, i.e. the zenith is assumed to be closer than the horizon. The Ebbinghaus Illusion doesn’t work as an explanation, because small clouds can surround the Moon high overhead, as in the illustration, but it does not look any bigger.

  15. Frank Reed

    Interesting. The creator of the diagram comparing the Moon at apogee and perigee (someone in the graphics department for NASA’s public relations dept.?) has made a common error. The Moon at apogee has been drawn darker. This is a mistake. The Moon is fainter at apogee in accordance with the usual inverse square law but ONLY because it is smaller in apparent area. Its face, its brightness for any "square minute of arc", would be the same. Even if it were ten million miles away from the Earth, if it was nearly at the same distance from the Sun, its brightness per unit are (more correctly "per unit solid angle") would be just the same. The Moon should not be shown looking duskier, greyer, darker when at apogee. It should only be smaller by that modest 14%.

  16. Rick Russell

    Although you’re right to point out that the rarity of the "super moon" is a myth, I think it’s a little disingenuous to suggest that it’s only "7% larger" than an average full moon, or "14% bigger" than the moon at apogee.

    The human sense of the size of objects is also affected by the apparent area of the object. In that respect, the super moon is more impressive, at 14% and 30% larger in area than an average moon or a small moon, respectively.

    BTW, this page does a fantastic job discussing the differences between the perigee and apogee of the moon:

    http://www.fourmilab.ch/earthview/moon_ap_per.html

  17. Fernando Rodrigues

    It really baffles me how some people dedicated to Astronomy (both professionally and in a non professional way) can write stuff in blogs that are either useless or damaging. Arguing that you don’t need trig calculations really makes me thing the person reading the post did not understand ist intention and is also out of context of what is being discussed here. Another issue is the note itself. We pretend to be so scientifically correct that we try to de-mystify the super moon concept. Why do it? On the contrary, lets use the media hype to bring people to our observatories and astronomy clubs, let people be amused by other things we can show them through a telescope a movie or presentation. There is a lot of misinformation, ignorance and lack of interest out there from the general public not to use the hype as a tool to bring more people in, create outreach and show other things. In our association we do a lot of noise when a super moon happens just because we know that hundreds of people will line up at the observatory door to peak into our telescopes and watch our movies. It makes more sense to use a myth than trying to downgrade it. Human history itself is made of myths. ‘Astronomy people" have to be better marketers and "business people" than simply mathematical and logic beings!!

  18. Frank Reed

    Fernando, you wrote: " Arguing that you don’t need trig calculations really makes me thing the person reading the post did not understand its intention and is also out of context of what is being discussed here. " Ha! Sorry you so mis-understood that little comment from me! You must have been skimming a little too fast. It was a reply to a PREVIOUS commenter who mentioned that he was working out an angular size with "trig". And so I pointed out for the benefit of anyone following along that you can work out angular sizes of astronomical objects (and scale models of astronomical geometries as in the case under discussion) without using any trig! For many people, it can be handy to know that they can do these things without anything more than simple ratios. And so that the message does not get lost, I will repeat: if you want the angular size of something in minutes of arc, take its linear dimension across the line of sight and divide by the distance to it. The result is an angle as a "natural number" (or "in radians"). To convert that to minutes of arc, just multiply by 3438. Just today, I had a little celestial navigation class use that simple calculation to figure out the distance to a ship offshore after measuring its angular size (and knowing its approximate length in feet). If you want to figure out the angular size of the Moon and confirm all this talk about Moon sizes or find out how much variation there is, just take the Moon’s diameter in miles and divide by its distance in miles and then multiply by 3438. On average you’ll get something like 31′. Then compare with its distance at various possible perigee distances (they’re not constant). You don’t have to trust some web site, or some Facebook page, or the TV weatherman. You can work it out for yourself using grade-school arithmetic. — ReedNavigation.com

  19. Frank Reed

    Fernando you wrote: "There is a lot of misinformation, ignorance and lack of interest out there from the general public not to use the hype as a tool to bring more people in" So you have to SPREAD misinformation to defeat misinformation?? I don’t know… That’s a slippery slope. How corrupt will you eventually be? The History Channel on (US) television is an excellent example of the sort of "stinking mess" you can find yourself in when you get to the bottom of that slippery slope. They began ten years ago adding more "exotic" and "speculative" topics to their programming and now it’s just "ancient aliens" hype and schlock. But they’re selling ads and making money so it’s ok, right? On the other hand, I do believe that the astronomical community should stop worrying about where the expression "supermoon" came and simply define it to be the closest perigee Full Moon in a cycle. Then there would be one every year to a year and half –a nice interval– and it would have a real fixed meaning. Whether you can see it visually would be a different matter (OBVIOUSLY, you can’t). But eagerly promoting a poor concept because you otherwise can’t get people interested in your observatory is… well… to put it bluntly, shameless. You are in good company though. The perpetually shameless editors at space.com have shelved the "killer asteroid of the week" story and instead this weekend devoted practically their entire site to the Supermoon! Yep. You are in very good company.

  20. Bob Sills

    The difference between the full moon in May and the full moon in June (the "supermoon") is like the difference between a 12-inch and a 12.007-inch pizza. True, you get an extra 90 microns of pepperoni at the edge, but you’d be hard-pressed to notice the difference. I’m sure that some people looked at the moon last night and were disappointed that it didn’t fill half the sky. Astronomers want to generate enthusiasm for their field, and some (Carl Sagan, Neil deGrasse Tyson) do it very well and honestly. Sacrificing integrity to drum up sales might work in business marketing, but I don’t think it’s a good technique in science. If we make a big fuss over astronomical non-events, people will conclude that we can never be trusted.

  21. Bob Sills

    correction to last post: Sorry — I misplaced a decimal point, and should have compared a 12-inch pizza to a 12.07-inch pizza — almost a full millimeter of extra pepperoni around the edges.

  22. N Wilson

    Is this June, 2013, brighter that other supermoons because it is occurring near the summer solstice? I noticed that colors were distinguishable last night (6/22/2013). I think supermoons this close to the solstice must be pretty rare. I think it was a pretty rare and spectacular event to actually see in color by the light of the moon

  23. mike.j

    Isaw the moon this morning, i new it would look biger on then horision and it sure seemed bigger and a whole lot flatter, WOW. Thanks for your explanation it puts everything into perspective.

  24. Fernando Rodriguez

    Some people don’t get it. First of all, our Association is considered one of the top Outreach Organizations in the country by the Night Sky Network. We do outreach at Museums, Private company events, Elementary and Middle Schools, Libraries, you name it. We open our observatory for the public on Saturdays and all is done for free. The media will continue to use the hype of astronomical events and not explain correctly to the public and mislead people with information. That is a fact and a reality that none of us can change or will change. it is there. So there are two ways to deal with it. Complain in a blog that only members of our community read or simply use them to drive people into our events and explain everything correctly. To insinuate its our only way to get people in our observatory shows lack of information and is quite offensive. I really don’t like people stating things they know nothing about. "Spread misinformation to defeat misinformation"?? Where did that come from I did not write that nor implied it. Calling us corrupt? We do not create the hype on the media my friend. People come to us and we explain. “Sacrificing integrity to drum up sales”? Where do you people read this? What sales are you talking about? Did you guys actually read my post? I am only stating that the hype is out there and people come to ask questions. You will never change the media. So be proactive and do something about it. Like explaining things to people beside a telescope. I never said we should create misinformation nor implied sacrificing integrity. You invented those words. Again I never said we should create misinformation. BTW any of you do any outreach for free?? Do you guys really think anything gets corrected with a note on S&T where a few hundred thousand people read this compared to 30 or 40 million who watch the evening news? Why not write something about the event explain it and encourage people to go to the nearest observatory or Astronomy Club?

  25. Frank Reed

    Sorry, Fernando, but you’re merely proving that this is indeed a "shameless" activity for you, for better or worse. I find that most unfortunate. Also your belief that "you will never change the media" is really the heart of the problem. If you believe you are powerless, then you are indeed powerless. The "media" are not some unstoppable force of Nature. For the most part, they will repeat what they are given. Journalism, with exceptions, is a passing fad in history…. But now that the "big day" has passed, you are off the hook. Your arguments no longer apply. So go out today and post on your Facebook page and you web site and wherever you can the TRUTH about this pseudo-phenomenon. The Supermoon is a pop culture tall tale, a popular delusion, and an example of the power of suggestion. SURELY some children in your target audience were disappointed by this "show" over the weekend and complained bitterly to the deaf ears of credulous adults, "I don’t see what the big deal is! It looks like any normal Full Moon!" And they were right. They, of course, are analogous to the child in Andersen’s "Emperor’s New Clothes" who is the only one to believe his senses and state plainly that the emperor is naked. Those who gain knowledge from their senses and their skepticism of "given knowledge" are the true scientists out there.

  26. Graham Wolf

    Our NZ media went "bananas" over the Supermoon too. But most media over here, were far more restrained… a couple of live interviews from me on national talkback:- Radiolive!, plus a detailed Press Release from Alan Gilmore at Mt John Observatory certainly helped there.

    Frankly the Supermoon belongs in the same trash compacvtor as the Jupiter effect, Neil and Buzz doing Apollo 11 ina Hollywood Studio, NASA being run by Aliens, the Myan Calendar apocalypse, Halley’s Comet crashing into the Earth… and so forth.

    Late last week in NZ we had a 200-210 Kph storm just a few km down the road, and parts of the Hutt valley look like Hiroshime the day after the bomb. And no… the "Supernmoon" had absolutely nothing to do with it.

    It’s called the real world!

    The S&T website gives an excellent breakdown as to the various causes of "distortions" and "misconceptions" re the moons "percieved" diameter… well done! But you just can’t tell conspiracy theorists out there, what they plainly don’t want to hear.

    Yes… I looked at the SuperMoon the other night, and the previous Supermoon. Nice to look at, but I’d frankly prefer another C/2006P1 McNaught. Now, THAT was surreal…. how about it Rob, can you give the Oort Cloud another "jiggle" from Coonanbarrabran, and zend another super-comet our way, please?

    Regards to all

    Graham Wolf:- Lower Hutt, New Zealand.

  27. Tom Hoffelder

    Thank you Ms. Balouchi. Thank you thank you thank you! I’ve been trying to say this for years! And comparing the moon (naked eye) to a 19 inch TV may be an apples vs oranges thing. The fact that the moon is only around a 1/2 degree in diameter has to be considered. The angle subtended by a 19 inch TV of course depends on how close you are to it, but chances are it is considerably more than 1/2 degree. My guess is that if you sat far enough away from the large and small TVs to make them the same size as the moon at apogee and perigee, you’d have a hard time seeing much difference in the image. This would especially be true if you didn’t have the two side by side to compare, which is of course the case with slightly different sized moons.

  28. rocksnstarsTom Hoffelder

    How about this? Print the NASA comparison so that the small one is 2 inches in diameter. Then cut each one out and paste in the center of a 4×4 inch piece of black paper. Next have a friend secretly pick one and hold it up 19 feet away from you. About a month later, have the friend hold the other one up at the same distance, and then see if you can tell which is which. True, you have a 50/50 chance, so go for 4 out of 7. And that’s the maximum difference, not the difference between average and super.

    Frank, good point! I use the inverse of that (1 arc minute ~ 3 times 10 to the -4 radians) all the time to estimate the light year diameter of galaxies I’m looking at in the scope, based on the distance.)

  29. Patricia Shaw

    Perigee Full Moon, if rising after sunset, is a welcome opportunity to watch Full Moon rise or to host an event so that others may also enjoy this sight. "Several times a year" Full Moon rises prior to Sunset and is therefore a low contrast event which does not allow people to enjoy a horizon level spectacle or the full effect of illusion. Having observed moonrise under varied conditions, I have seen Moon present as a heralding glow, a citrine glint at far field’s edge, and as full orbs of red, orange, neon coral or even pale white in a still blue sky. Last month I hosted a May Perigee Full Moonrise hilltop watch. It was a lovely sight, and I didn’t hear anyone complaining. I did not host an event in June, as it was cloudy, but the Moon remained visible enough to enjoy navigating under its low path at a Saturday ‘super moon’ orienteering event. Had Sunday been clear I would have welcomed the opportunity to share its larger and brighter appearance with others once again.

  30. rocksnstarsTom Hoffelder

    Good point Frank! I use the inverse to estimate the actual size of galaxies I’m observing. One minute of arc is approx 3 times 10 to the -4 radian. I multiply that times the galaxy distance in my head.

    But back to superness, I present this as a reality check. Print out the NASA comparison in the article so that the small moon is 2 inches in diameter. Cut each of them out and paste in the center of identical size pieces of black paper. Have a friend secretly choose one and walk 19 feet away. (This will make it the same size as the moon in the sky, believe it or not!) Stare at it for awhile and then repeat a month later with the other one. Now say which one was the super moon. Right, there is a 50/50 chance of being correct, so it should be 4 out of 7. And that’s comparing the extremes, not the average and super! I know I couldn’t tell the difference.

  31. rocksnstarsTom Hoffelder

    Today, 7/22/13, THE MOON IS FULL – go out and "measure" it! With a ruler 12 inches away from your eye, hold it up to the moon. You will find the dia to be 1/10th of an inch. The difference between an average moon and a super moon (and the smallest moon) is 7%. 7% of 1/10th inch is LESS THAN 1/100th of an inch! Neither your eye nor the ruler is calibrated to register 1/100th of an inch. Therefore, every full moon, from the smallest to the largest, will measure 1/10th of an inch. And that is the bottom line of why the super moon is super silly.

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