The Supermoon stuff? AGAIN?

By Phil Plait | May 2, 2012 10:37 am

Sigh.

You may’ve seen some folks writing about this weekend’s so-called Supermoon. I suppose I’m not surprised, but it’s still irritating. Why? Because it’s just hype (and to get this out of the way immediately, will have no real effect on the Earth, either). Here’s the scoop.

This weekend, on the night of May 5/6, the Moon will be full. This happens every 29 days or so when the Moon is opposite the Sun in the sky, and we see its face fully illuminated.

As it happens, the Moon’s orbit is elliptical, and so sometimes the Moon is a bit closer to the Earth than other times. Every now and again the Moon is full when it’s also closest to Earth — the point in its orbit called perigee. May 5th is one of those times.

What does this mean? Well, it means the Moon is closer, so it will appear a bit bigger and brighter than usual. But here’s the thing: you’d never know. Seriously, to the eye it’ll look exactly the same as it always does when it’s full. The Moon is actually pretty small in the sky — if you don’t believe me, go outside tonight, find the Moon, and hold your thumb up at arm’s length next to it; it’ll easily cover the Moon entirely (my thumb is 2 – 3 times wider than the Moon). A small change in its size is something that’s really hard to see.

To be specific, according to Fourmilab, the Moon will be 356,953 kilometers from Earth when it’s full. However, last month, on April 7, when it was full it was about 358,313 km away. That’s a difference of 1400 km, less than 1%. So really, the size of the full Moon this weekend won’t be any different than it was last month, and no one was writing about it then. And to show I’m not being biased, take a look at when the Moon was full near apogee — the most distant point in its orbit. That’ll happen in late November of 2012, when it’ll be at a distance of 406,364 km. That’s still only a difference of less than 14%.

That’s a pretty small change, not enough to notice by eye. To see the difference in this weekend’s full Moon, you’d need to take a picture and compare its size to how it looks at some other full Moon. The picture above shows that pretty well (click to enlunenate). You can see the difference between perigee and apogee Moons there easily, but that’s because the Moons are side-by-side. This weekend, with the rising Moon all by itself in the sky, you have nothing to compare it to. It’ll look the same as it always does (and don’t confuse the rising Moon looking huge due to the Moon Illusion with this Supermoon silliness).

That hasn’t stopped some news venues touting this as a "Supermoon". I’m seeing it on websites, on Twitter, and getting email about it, and like I said, it’s irritating (and I’ll add the idea for this whole as well as the term "Supermoon" were started by an astrologer, so draw your own conclusions there). I’m all for encouraging people to go out and look at the Moon, but it shouldn’t be under false pretenses. I mean, c’mon: it’s the Moon! It’s bright and silvery and lovely and you can see features with your naked eye and with a telescope you’ll see tons more!

Even though it’s not super, the Moon isn’t exactly mild mannered either. So if you can, go out and look. Not just this weekend, but any time! Use a telescope, or binoculars, or just go and look anyway. Because it’s pretty, and it’s ours, and it’s always worth a look.

Image credits: Apogee/Perigee: Anthony Ayiomamitis; Rising Moon: me!


Related Posts:

- Kryptonite for the supermoon
- Supermoon Skeptic Check
- No, the “supermoon” didn’t cause the Japanese earthquake
- The proxigian, perigean Moon

Comments (83)

  1. Try being a bit more sensitive just because I am little larger does not mean when I moon someone it is super. Oh you mean the moon in the sky.

  2. Alan

    OK, so Supermoon is fiction. What about Batmoon, Spidermoon, and all the other superhero-moons?

  3. Kevin Kirby

    Better than that “Mars as big as the moon!” crap that circulates every so often. But, not by much.

    Alan: I’m a fan of Doctor Manhatmoon.

  4. Doug

    I took this “super moon” talk to mean that it is both full and at its closest, not just that it is closest. Your article seems to focus only on the size change, while you do say “every now and then” with regards to the full/close concept, and the rest of your article is ripe with data, it would have been nice for you to include (certainly to someone such as myself who literally just bought his first telescope and has so much to learn) information on just how often or what the odds are that this happens.

    When you say, “That’s still only a difference of less than 14%.” it strikes me as thought you may be a little jaded… and this entire article comes off as elitist. If anything, I would have thought – the astrology roots notwithstanding – that it would be a great, accessible way to promote the amazing nature of the universe in all of its statistical glory.

    You could have just as easily spun the article in the oposite direction – emphasizing that the moon is a whole 14% larger (in what other discipline would a professional dismiss a 14% change in a measure?) and only happens [so often], especially while full!

    In short, have you lost your taste for simple wonder? That is not a very inviting notion to a budding amateur astronomer.

  5. “Always worth a look” can’t be emphasized enough, especially because from one night to the next you get a slightly different view. It’s like 29 astronomical objects in one!

  6. Gopal

    Doctor Manhatmoon is cool, but Ironmoon is better

  7. Ward

    Alan – your comment made me hear something in my head. (Spoken/sung as from the old TV Series) “Wonder Womoon!”

  8. Supermoon’s nemesis is Lex Lunar.

  9. I’m going to hang out at Royal Hope Hospital and hope Smith and Jones show up. Then I might actually go *to* the Moon. Now *that* would definitely be “super”.

  10. Naked Bunny with a Whip

    So when is the moon getting blown out of orbit so this will stop coming up?

  11. Bryan

    If it persuades more people to look up at night and interested in Astronomy, then I say let people call it what they want.

  12. Tziva

    You know, the moon just wants to have his day. Let him feel super. It will be good for his self esteem. Why you gotta take that away from him?

    It’s okay, Moon, *I* think you’re superduper.

  13. ceramicfundamentalist

    @ bryan #8

    yeah, except there’s nothing more stifling to budding interest than disappointment, and those who might go to look at the moon expecting it to be spectacularly different than last time they saw it will probably be disappointed and never bother to look again.

  14. Two weeks later, when the Moon is new and in eclipse, it’s also at apogee. So it’s smaller. That’s why it’s (at best) an annualar eclipse. It’s not big enough to cover the Sun.

    So Mars is bigger than the Moon, which isn’t as large as the Sun… Jeez. No, no! It’s an Opportunity (that’s the Spirit). It’s a teaching moment.

  15. Jay29

    Phil, you’ve been immortalized in Sci-ence again (http://sci-ence.org/night-of-the-super-moon/).

  16. mike burkhart

    If you think the moon will look big consider that when the moon formed it was munch closer to the Earth and would have been very big in the sky. It might have caused massive tides on Earth at this time . The moon is slowly drifting away form the Earth ,but it won’t leave orbit before the sun becomes a red giant.

  17. Jay29

    @Doug, while I’m willing to trust Phil’s conclusion that 14% won’t make a difference, I too am left wanting a little bit more. It’s true that 14% seems significant in most scientific venues, especially here when gravity is inversely proportional to distance squared! I would have liked to have seen some calculations (similar to those that show how constellations have no physical effect on Earth-bound humans) that show the difference in tidal forces from perigee to apogee, and WHY the “Supermoon” can’t cause earthquakes and other natural disasters.

  18. I’m looking at it from the perspective of a photographer. I’m planning on (weather permitting) getting some good shots of it as it comes over the horizon. That 14% makes a difference when you’re looking at it on the horizon.

  19. Jeff B

    @Doug (the new astronomer) and Jay29: I have to agree with you, this article seems jaded and elitist. Like the author is going, ho-hum, the moon is going to be full and at closest approach, no big deal. I have also just purchased TWO advanced telescopes and am getting back into an old hobby that I can now actually afford – both in terms of time and money. My fascination with the cosmos that can be viewed or photographed with a decent telescope (or the naked eye for that matter) has been renewed and I’m about to embark on a period of extended rediscovery of the objects out there that should be fascinating to everyone.

    I’m a member of the Cincinnati Astronomical Society and Saturday the club is hosting a big public outreach, inviting them to view the moon through a variety of instruments. And we’ve termed it a “Super Moon” event at the request of the local TV stations touting it. Sometimes ya gotta catch the people’s imagination and attention. Any chance to view the moon is a pretty awesome moment that most folks take for granted.

  20. Jamesonian

    I second Doug (#4). Why not celebrate this as a great marketing opportunity for astronomy? Get the kids to turn off the Xbox for a few minutes and go look at the moon. People love events, even somewhat contrived ones, and there’s nothing at all wrong with using such an event to further a worthy cause. Phil, you’re starting to sound like just another cranky old guy who looks for any chance to pounce on someone who doesn’t see things as you do. There are no facts in dispute, there’s no pseudoscience to debunk, it’s just the moon being full and close at the same time. Can’t we have fun with it?

  21. CB

    In short, have you lost your taste for simple wonder? That is not a very inviting notion to a budding amateur astronomer.

    Did you miss the part at the end where he encouraged you to go out and look at the moon because the moon is always awesome?

    Which smacks more of losing the taste for simple wonder: “Look at the moon because the moon is always cool and fun to look at” or “Let’s only look at the moon because it’s a rare supermoon! Not that crummy, regular moon.”

    That’s the “false pretenses” he was talking about. The moon will not be noticeably different than any other day. If you’re just excited about this event you’ll be disappointed — like my Mom was when she told me she went to look at the Blue Moon and it wasn’t blue. :P If that’s what it takes to get you to go look at the moon and you enjoy it, then fine (Phil says this), but you should enjoy the moon for what it is, not for what hyped-up crap the news says about it.

  22. Jay29 (17): In the post is a link to my article about the gravity of the Moon, showing that there is no connection (or at best a very weak one) between the Moon and earthquakes, and the gravity of the Moon is just not that much greater.

    Jeff B (19): Elitist? I actually make a big point in the last paragraph to let people know they should go out and observe it! My problem with this whole thing is that 1) it’s based on nonsense, b) you can’t see the difference, and γ) it’s being overhyped. It’s an interesting thing, sure, but I’m seeing a lot of ZOMG HUGE MOON kind of stuff. It’s silly.

  23. Jay29

    Thanks, Phil. I realized right before you posted that you included links to the details.

  24. Ians

    Doug and Jay29, you may want to read through the related articles links at the bottom of this article. Phil has covered this subject a good many times and much of the detail you are looking for is covered in them.

    Doug, the particular configuration of full moon and perigee being coincident occurs every 14 lunar cycles, there are 12.37 lunar cycles in a year so this happens slightly less often than once a year. the reason Phil comes of a little exasperated is because every once in a while fox news or some crank try to link the “supermoon” to natural disasters when there is absolutely no mechanism that hasn’t been present at least once in the 13 months and as far back in history as you can be bothered to calculate without triggering anything and yet it keeps coming up time and again. (It gets even sillier when you notice that no one ever gets excited about new moon at perigee even though that would produce even larger tides and therefore presumably trigger even more natural disasters if there were any link between tides and natural disasters, which there isn’t..)

  25. KC

    @Doug & Joy29

    I think you’re missing the point – it really isn’t 14% – it really only 1% difference when compared to last month or next month. The vast majority of people do not walk around with the average or minimum size of the moon memorized.

    Oddly enough “The Moon Illusion” (Google it) has a much greater effect on the appearance of the Moon than its actual diameter.

    @Kaessa – its not really that important…a zoom or telephoto lens can make a much bigger difference in how the moon appears in frame.

  26. Gary Miles

    I have to agree with Phil. Overhyping astronomy can be just as harmful when you lead people to believe they are going to see something different and unusual. Clearly, there is going to be little noticeable difference. I am all for making Moongazing fun and exciting, but not with misleading and/or incorrect information. Take the hype over Betelgeuse for instance. I cannot tell you how many times I have heard people tell that Betelgeuse is going to supernova tomorrow and will turn night into day. Even my own girlfriend told me that (now my ex because apparently I am such a buzzkill).

  27. Hevach

    Worse than hyping something people won’t even be able to see, if you use this for publicity, you risk the media recycling content and experts from the last time something called Super Moon made news. At best the distinction will be lost on most of them and rehashing is business as usual in an election year anyway, at worst they already know they get better readings with sensationalist bull than they do with science.

  28. Jeff B

    Phil, you’re right. I jumped at you a little too hard with the elitist comment and I apologize. It was just something I felt at that moment but which dissipated when I re-read the article – and after I spoke.

    My bet is that people WILL see something different and unusual because they rarely take the time to look at it otherwise. Making them THINK it’s bigger may cause them to see things they never saw looking at the “smaller” moon.

  29. Jeff B

    BTW, there are posts all over Facebook about this SUPER MOON appearing larger than ever. Thus the hype grows…

  30. Rob

    Doug: emphasizing that the moon is a whole 14% larger, and also other commenters:

    The moon is not in fact 14 percent larger than it would be at perigee. It appears to be 14 percent larger.

    The moon growing and shrinking in size would be a big deal. Its appearance in the sky really isn’t, especially since there’s no discernible difference from one month to another. It’s a cool visual effect if you take the time to compare it to the last time this happened, but it’s just silly to link it to tides, volcanoes, earthquakes, etc.

  31. Artor

    Last year when the super-Mars thing was going around, some friends of mine repeated the canard that tit would be as big as the moon. I was a little short with them as I pointed out NO; it’s only about twice Luna’s diameter, and still about 100 times as far away, even at it’s closest approach. I think they were annoyed at being corrected, but I couldn’t let it lie.

  32. Solius

    Kevin Kirby @ 3 wrote

    Better than that “Mars as big as the moon!”

    Only marginally, and August will be upon us again, soon. So, here we go again.

  33. I see no harm in the “Super Moon” moniker. I’ve always used it as a way to refer to the full Moon at perigee. It’s no different to me, than referring to the “Harvest Moon” as the full Moon closest to the September Equinox.

    If nothing else, they’re great arbitrary terms to refer to a specific full Moon.

    Plus, I agree with some of the others that it’s a great way to spark a conversation about the cosmos. Conversations regarding the cosmos generally become very involved and evolve substantially from the original discussion, all the while giving me a chance to plug the awesomeness of the Universe.

    For me, rather than rolling my eyes and becoming frustrated with those that don’t understand what the Super Moon is, I use it as an opportunity. Being smug might have its place, but in my opinion it’s wasted here.

  34. Christine P.

    I’m sure the Super-Moon will circulate every year now, until finally enough people realize that it doesn’t look any different than every other full Moon.

    @Jay29 (#15) – Hah! Zombie Phil!

  35. Pete Jackson

    @Jay29 (17): You make an excellent point about the effects on the tides. Since the tidal ‘force’ is dependent on the inverse cube of the distance (you calculus junkies will understand this since the tidal ‘force’ is basically the derivative of the inverse-square gravitational force), the lunar tides from the perigee moon will be 42% greater than the lunar tides from the apogee moon! The total tide is the sum of the lunar and solar tides, with the solar tide being about half the lunar tide, so the total tide will still be about 30% greater for the perigee full moon than for the apogee full moon.

    Now, I would consider that a sizable effect, especially if you live near the Bay of Fundy!

  36. I know… Use the “supermoon” hype to get people out to some astronomy club’s meeting. Show them the Moon through everything from “super-duper” telescopes down to binoculars, so they can use something they may have at home. Show them the wonders.

    Then, end it with “And you know what? You can see a full Moon every month! And take a look every day, and notice the changes in the shadows. Notice the mountains and the craters. And when you’re done looking at the Moon each night, check out the million other things up in the sky.”

  37. Yes, Ken (#34)!

  38. KC

    Well I dunno I’m all for popularizing astronomy but the ends don’t justify the means. Is this what we’ve come to – the only way to promote science and astronomy is with exaggerations and fabrications?

  39. KC (#36), I don’t think anyone is advocating for fabrications or exaggerations. Saying that this full Moon is the closest one we’ll see all year isn’t a fabrication nor an exaggeration. When I talk to people about the Super Moon I generally explain it like Phil did above, but I just ditch the “Ugh!” and substitute with, “Cool, huh?!”

  40. VinceRN

    The moon is always super!

  41. Well, I don’t know about you, but I’m going to listen to the Moonlight Sonata and enjoy it as it rises before sundown. The moon always looks better when your listening to certain types of music. But of course, a scientist wouldn’t know that sort of thing.

  42. Patrick

    Enlunenate! My new favorite word, thanks.

  43. Mike Saunders

    Care to give me ONLY 14% of your yearly income Phil? You can’t tell the difference!

    Seriously, it gets people talking about the moon, and it isn’t false. The moon is larger!

  44. Sawdust Sam

    Rob @31: ‘The moon is not in fact 14 percent larger than it would be at perigee. It appears to be 14 percent larger. The moon growing and shrinking in size would be a big deal.

    David Niven’s autobiography was called ‘The Moon’s a Balloon’. This explains everything.

  45. Nigel Depledge

    Jay29 (17) said:

    @Doug, while I’m willing to trust Phil’s conclusion that 14% won’t make a difference, I too am left wanting a little bit more. It’s true that 14% seems significant in most scientific venues, especially here when gravity is inversely proportional to distance squared! I would have liked to have seen some calculations (similar to those that show how constellations have no physical effect on Earth-bound humans) that show the difference in tidal forces from perigee to apogee, and WHY the “Supermoon” can’t cause earthquakes and other natural disasters.

    Well, aside from the fact that the “supermoon” will be less than 1% closer to Earth than last month’s full moon, and aside from the fact that the moon goes through both apogee and perigee every single month without there being any noticeable effect, did you not read the related posts?

  46. Nigel Depledge

    Jamesonian (20) said:

    I second Doug (#4). Why not celebrate this as a great marketing opportunity for astronomy? Get the kids to turn off the Xbox for a few minutes and go look at the moon. People love events, even somewhat contrived ones, and there’s nothing at all wrong with using such an event to further a worthy cause. Phil, you’re starting to sound like just another cranky old guy who looks for any chance to pounce on someone who doesn’t see things as you do. There are no facts in dispute, there’s no pseudoscience to debunk, it’s just the moon being full and close at the same time. Can’t we have fun with it?

    Maybe so, but the “supermoon” will be less than 1% closer to Earth than last month’s full moon – a difference that will be nigh on impossible to detect by eye even with a telescope.

    The term “supermoon” might be a contrived event, but it builds an unrealistic expectation that the moon will somehow look different from usual. Which, unless you have some pretty precise measuring equipment trained on it, it won’t.

  47. Pete Lambert

    It’s a tacky name alright. But I think you’re letting that blind you to the additional brightness (I PUN!) as the moon will appear to have something like 35% more surface area, based on a very rough estimation from your handy picture. Don’t under estimate the law of big shiny things seeming to get bigger and shinier when they are nearer.

  48. Calli Arcale

    There is one big negative impact of a perigee full Moon — it’s about the only way the Moon could screw with this weekend’s meteor shower more. ;-) Mind you, it’s probably gonna rain for me this weekend anyway, and I’m in the northern hemisphere so the eta aquarids won’t be as nice as they could be anyway. But gosh darn it, I’m still gonna complain! :-D

  49. Oh mercy. USA Today ran with this silly story today, and their story includes this classic piece of horrible journalism:

    “That’s not to say a supermoon hasn’t caused damage in the past: It’s believed that a supermoon event may have contributed to the sinking of the Titanic 100 years ago.”

    It’s believed. By whom? By people who are wrong?

  50. @Nigel (48): “it builds an unrealistic expectation that the moon will somehow look different from usual”

    Kind of like printing big, detailed, Hubble-quality photos of planets and nebula on the packaging of amateur 60mm telescopes. I understand why they do it, but it ultimately results in disappointment for beginning stargazers. And that disappointment can easily lead to losing interest altogether.

  51. Solius

    Cris (without an H) wrote:

    Oh mercy. USA Today ran with this silly story today, and their story includes this classic piece of horrible journalism

    It’s mostly speculation, but it is a valid hypothesis. See April’s issue of Sky and Telescope– it was the lead article.

  52. Lizbet

    The farmers almanac refers to this moon as the Flower Moon. Folklore has it that as the spring flowers were in bloom, the bright light allowed the Indians to see the fields of flowers at night, mirroring their color & beauty. The media becoming aware of this educates others. Good for them, and about time.

  53. One way in which a perigean Full or New Moon is very noticeable is through its effect on the tides. A few percent decrease in distance is multiplied threefold, as the tidal effect is inversely proportional to distance-cubed. Here in Nova Scotia, where the tides are already large in the Bay of Fundy, this amplified tidal range is astonishing to experience. The 2012 RASC Observer’s Handbook notes April 6–9, May 6–9, and June 3–6 as periods during which the Full Moon near perigee results in large tides.

  54. Nigel Depledge

    Pete Lambert (49) said:

    . . . the moon will appear to have something like 35% more surface area, based on a very rough estimation from your handy picture.

    Well, compared to an apogean full moon, yes. But compared to last month’s full moon, it might only be 1% (-ish) brighter. How is anyone going to notice that?

    The thing is that it takes many months for the full moon to transition from coinciding with apogee to coinciding with perigee, during which time, each full moon is but a little closer than the last. You would never see a perigean full moon following just one month after an apogean full moon. And even so, you almost certainly wouldn’t notice the difference unless you carried out a photographic comparison, or took a precise measurement of the moon’s apparent diameter when it is full, and then conducted a numerical comparison.

  55. jess

    After reading your article I was left with nothing but disgust. So what if you can’t actually tell a difference with the naked eye. From what I understand it is a legitimate occurrence. It really will be bigger and brighter! So what are you complaining about? People might actually get up off the couch and away from a computer to see an amazing natural beautiful sight. Maybe it will start a spark in someone to get them more excited about astronomy. Maybe it will encourage someone to see and appreciate the simple pleasures in life. Maybe it will encourage someone to be more of an optimist rather than such a pessimist like you. The only disgust I see from the “super moon” stories is you trying to make something negative out of an amazing true occurance.

  56. oolz

    what’s the point of publishing an article that mocks the hype, but then goes on to confirm exactly what the hype is saying, that it’s a nice, slightly bigger than average, bright, full moon? This article seems no different than some rant you’d read from a kid whose favorite band hit it big and now everyone wants to go see them.

  57. Alan

    You need to find a new profession. You no longer see the benefit and bringing new people into astronomy and showing them the wonders. Calling it a supermoon spikes interest in the night sky and in the moon. But we’d never know from your eyeore attitude….

  58. headjay

    The point is that there is a closest and furthest point for the moon every month. It’s just that the closest point coincides with a full moon only now and then. The media is just not interested in a closest half moon or crescent moon etc.

  59. The curious thing is that this supermoon is so precise. One site said that the exact moment of closest approach is only about one minute off from the exact moment of being full. The last time was 50 minutes off. Admittedly that is something which can’t be seen with the naked eye but it is interesting.

    If we had a lunar eclipse during a super moon would it still be a super moon?

  60. digitalatheist

    @#10 So when is the moon getting blown out of orbit so this will stop coming up?

    13SEP1999 :-P ;-)

  61. Jennipoo

    Who cares if it’s off by a few thousand km and not mean much to the naked eye? If it gets people / general public curious and talking about astronomy and wanting to know more…that’s great! :)

  62. snortlaugh

    I go outside. I look a teh moon. Liked it much. Moon pretty and is bigger. I have good time.

  63. Bob Collins

    So you poo-poo and hohum this event. Yet you use the hyperbole of the silvery moon! Silvery indeed, every time I take pics or look, it is white gray or orange, never seen it silvery.

  64. Jack

    Ironically, I hear more hype from people looking down at their noses at the Supermoon term than anything else. What difference does it make what people call it? We ought to be happy that lots of people (who we are no better than) are suddenly taking an interest in astronomy. As pointed out in this very article, nothing people are saying is technically inaccurate, even if they will be a bit underwhelmed. I honestly would’ve hoped Dr. Plait would be on the other side of this issue.

  65. kali

    You are hilarious. I hope you were smart enough to look outside and see the visible difference. The moon was huge and yellow and beautiful. Obviously larger. Your vision must be challanged. It’s sad to see people like you are permitted to publish “news”. Ha.

  66. Thank you for this. I was able to argue Pub Trivia points for using perigee instead of “supermoon” this week.

    Thank you for enlightening me.

    Also, I’m one of those guys who argues for Pub Trivia points.

  67. Matt B.

    The real problem of the term “supermoon” is that it encourages qualitative thinking in a quantitative situation.

  68. John H

    Larger than which other month’s full moon Kali? You say it looked larger. Which other full moon were you comparing it to?

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