SUNSET: 
22Saturday's full Moon will be the year's closest — but not by enough to draw attention.
"The superstitious among us should beware of extra-big werewolves this weekend," warns Time magazine. For some reason, the world's news media are all aflutter over Saturday night's full Moon.
The full Moon of May 5, 2012, appears just 8% larger than the average full Moon.
S&T: Sean Walker
May is the month this year when full Moon occurs closest to perigee, the point where the Moon is closest to Earth in its monthly orbit. But the Moon will be only 8% closer and larger than average. That's not enough to notice unless you're a very careful moonwatcher. Or use measuring tools.
And, this full Moon will shine only 0.16 magnitude brighter than average. That's only slightly more of a brightness difference than a skilled variable-star observer can just detect.
You can see the difference in a side-by-side comparison like the one above. But looking at the Moon by itself? Not likely.
If this is a "Supermoon," I guess Superman can only bench-press 108 pounds if I can bench-press 100.
If you want to compare Saturday's lunar apparition to the Moon at its very farthest, you can double those numbers. They're still not a lot.
Do go out and take a careful look. But beware of the power of suggestion. As my S&T colleague Tony Flanders just popped his head in to say, "You know some people are going to swear the Moon is just incredibly huge. If you'd told them the Moon was biggest when it was actually the smallest of the year, they'd probably say the same thing."
When it comes to science stories, some news editors never seem to grasp what the engineer's T-shirt says: "If you don't know it in numbers, you don't know it at all."
Comments
Anthony Barreiro
May 4, 2012 at 12:03 pm
Anything that gets people thinking about and looking at the night sky is a good thing. And for those of us who live near the ocean, tides will be very high and very low, making for good tidepooling, thanks to this perigee full Moon.
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Anthony Barreiro
May 4, 2012 at 12:03 pm
Anything that gets people thinking about and looking at the night sky is a good thing. And for those of us who live near the ocean, tides will be very high and very low, making for good tidepooling, thanks to this perigee full Moon.
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Daniel Fischer
May 4, 2012 at 4:34 pm
Too bad Sky & Tel. editors aren't looking at the full moon more often: then they might notice that you can see the ellipticity of the lunar orbit with your unaided eye and without further measuring tools pretty easily. I wouldn't have believed that myself until early last year, but the inadvertent 'blind test' I underwent - and doczmented in http://cosmos4u.blogspot.de/2011/03/if-you-know-your-full-moon-you-will.html - leaves no doubt. In fact, I've since made a little sport out of deliberately not looking up the lunar distance before guessing it visually around full moon: it works surprisingly well. Encourage your readers to do the same instead of telling them it can't be done! Here, for once, the "supermoon"-crazy mass media actually tell a better story than all those science and skeptic websites ...
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Scott
May 5, 2012 at 7:03 am
I wonder if editors are confused by the moon illusion? Many people I know are sure the moon is sometimes extra large (when they happen to see it near the horizon). People who see the moon at moonrise this weekend will probably think, "Wow! It's true!" and those who look up late at night will shake their heads and think, "I know I've seen the moon much, much bigger than that!"
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steve guskjolen
May 5, 2012 at 7:53 am
I'm glad the editors are a bit skeptical about the mainstream medias giddiness. While it's great that people will be courious and willing to take a look, I'm afraid the majority of people, after hearing the hype will witness 'super moon' and think, "what the heck?"
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Robert Dodd
May 5, 2012 at 11:52 am
While it will be about 8% closer, it will actually appear about 14% larger by area...
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Kelly Beatty
May 5, 2012 at 6:04 pm
Robert... in Alan's defense, he said the Moon would be 8% larger, which is admittedly ambiguous, but I submit most people would equate "larger" with "diameter." thus no error.
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Kelly Beatty
May 5, 2012 at 6:10 pm
Daniel... your experience is hardly convincing "proof" that we "got it wrong here." OK, so you looked up one time and saw the Moon unusually large when it, in fact, was. and this proves what? in our collective experience, most casual skywatchers have no idea how large the Moon appears, let alone how many can notice a variation in area. ask 10 of your non-astro friends to make the same assessment you did, let at least 7 of them get it right, then you'll have something defensible.
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George Blue
May 6, 2012 at 5:45 am
Last night the moon was full and we were discussing "super moon" with the neighbors. I suggested we measure it, using a measuring device we'd be sure to have around next full moon to compare - so we extended our arms at full length and noted how much of the moon our thumb would cover. My thumb happened to cover it exactly, so it will be fun to see the difference next month.
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Bruce
May 6, 2012 at 7:01 am
Very practical suggestion, George. Last night I was clouded out, but I look forward to using your idea as soon as possible.
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jaime
May 6, 2012 at 8:45 am
Excelent topic and photos comparing the sizes, please comment on the even bigger eye effect in some areas, up to 14% bigger ?? I invite to wwww.Yahushah.net/astronomia.html
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Harry Hamill
May 7, 2012 at 2:28 am
I'd have to disagree strongly with Mr. Fischer about the S&T coverage of the 'supermoon'. It is factual, informative and, as one would expect, unsensational. Refreshingly different from the nonsense which has appeared in much of the British press at least. Mr. Fischer's comments about his 'experiment' 'leaving no doubt' reveal a lack of understanding of what science is about and how it works.
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Jean Loup
May 8, 2012 at 11:16 am
Mr George Blue:
Your idea is excellent, provided you measure again in 6 months/6 full moons time. The next full moon (this May) will look very much the same size. It takes a while crocodile for the moon to aquire distance away from Earth, not all of a sudden in one month/next full moon!
Most noticeable difference in size for rule of thumb will be at perigee. Me, I do notice the difference because I go out every night to watch the sky with clear atmosphere ... well, recently the Popocateptl volcano has been throwing out ashes (not blaming Moon at all!) and we see the full moon with a yellowish tinge. But in the rain season to start soon, the atmosphere will clear out again.
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Jean Loup
May 8, 2012 at 11:24 am
I live North of Cuernavaca city, at Sta. Maria Ahuacatitlan near the woods, at 18°52′N 99°15′W with a 1,650 m (5,410 ft) elevation. Glare from Cuernavaca city lights at South sky is below 30 degrees.
Un Abrazo from Mexico!
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Shirley Barron
May 8, 2012 at 6:59 pm
Interestingly, a fairly knowledgeable friend called me Sat. afternoon & told me he heard the moon would be "16 times brighter than usual." "Hmmm," I said, not wanting to get in an argument. I did observe the full moon & it was pretty big & pretty bright, & the features were easier than usual to see during full phase, but where did that ridiculous figure come from? Did some media person hear "16 hundredths of a magnitude" and interpret it as "16 times"? I'm really curious......
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tom hoffelder
May 10, 2012 at 12:20 pm
I totally agree with this article! The hype was ridiculous and totally misleading. People were led to believe they could see the difference in the moon and therefore it did look bigger, because they expected it to. If the media would have told the whole story, that yes this full moon is the biggest of the year, but visually you will not be able to tell that, then it would be OK. But instead typical media sensationalism was the name of the game. And how much higher were the tides than when the full moon is at an average distance? The next to last paragraph says it all. Personally, I consider the media's coverage to be basically a lie, and liars are not my favorite people.
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Matthias Dopleb
May 11, 2012 at 11:46 pm
I have looked into the matter more closely and found some really remarkable full moons: For instance, on December 24, 1787, just after a partial lunar eclipse, the full moon had an apparent diameter of 34 arcminutes and 7 arcseconds at its zenith (for an observer in South East Asia) - with a phase angle of just 1.58°, making it one of the brightest full moons for many centuries (mag -12.92). It will be outstripped by the full moon of February 1, 2762, being 13 kilometres closer to Earth (356,572 km). 4-5 millennia ago the moon was even closer, but it is gradually moving away from us (4 cm per year)...
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Frank Reed
May 13, 2012 at 1:29 pm
George above describes the size of the Full Moon as follows: "My thumb happened to cover it exactly." HA! George, you either have incredibly tiny thumbs or amazingly long arms. The apparent size of the Moon is MUCH smaller than the apparent width of an average thumb at arm's length. In fact, you can easily win bets on this. Lay out some common coins on a table (I'll be US-centric here and assume American coins). Ask a group of people which coin held at arm's length will exactly cover up the Moon as seen in the sky: a quarter, a nickel, a penny, or a dime? In my experience, most people will select a penny, and if the Moon illusion is in play (when the Moon is near the horizon) many will pick a quarter (!). They're pretty sure that a dime is too small. In fact, all of these coins are much too big. In comparison to a penny held at arm's length, the Moon is about the same size as Lincoln's face on the coin. An angle of 34 minutes of arc --the size of the Moon at perigee-- is a ratio of about 1-to-101. The ratio at apogee is more like 1-to-118. So suppose your arm's length reach is 24 inches. An object between 0.20 (at apogee) and 0.25 inches across (at perigee) would be the right size to cover the Moon exactly. Sorry, George, I don't believe your thumbs are that small. 🙂 And you can thank your stars that the Moon is NOT that big in the sky. Since the tidal accelerations are proportional to the Moon's angular diameter CUBED, if the Moon was close enough to appear two degrees across (thumb-sized) the tides would be 64 times greater in range. Where I live the tidal range is about four feet. With a two-degree-wide Moon, the tidal range would be around 250 feet, and the inter-tidal zone would be hundreds of miles wide.
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Frank Reed
May 13, 2012 at 1:35 pm
I agree completely that this was a case of media mania, but let's be honest, S&T's editors committed much the same "sin" last month when they jumped on the Titanic bandwagon and published the patently silly claim that the perigee spring tides in January of 1912 were sufficiently unusual to have released an unusual number of icebergs from the shores of Labrador. There are many factors involved in the tides, and the tides that January were not unusual. Unfortunately, the authors feel for the work of that obsessed oceanographer, Fergus Wood. This was just as much "perigee mania" as this latest "supermoon" hype. And worse that, it was POOR science.
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Bruce
May 14, 2012 at 9:10 pm
Frank, I have amazingly long arms. (I'm 6'5", and I've heard little kids say, "Look mommy, a Giant!) My thumbs are proportional. A nickname I had in high school was Caveman.
So after reading the first of your two posts this morning I was eager to test your debunking of the now international craze of Thumbing the Moon, invented by George Blue. As I found your mathematical logic very compelling, I resolved to put it to the test "with all possible dispatch". Even though I realized that the moon was now far past the way over-trumpeted apogee and in it's waning phase, I reasoned that the range of sizes displayed by the moon aren't really all that large and that it should look fairly typical today and that I'd be able to extrapolate it's full size. So I lumbered forth from my cave/office around 10 AM, scanned the clear blue ecliptic and lo, there the crescent was. I extended my extensive arm to it's maximum extent and, I'll be, Frank Reed is absolutely right! I could have covered nearly two widths worth of our lessor luminary! In fact, I couldn't even Pinky the Moon! My little fingertip totally eclipsed our moon's entire diameter! So Mr. Reed, I salute your mathmatical skill, and your comment has been totally confirmed. A great big thumbs down on Thumbing the Moon.
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reptil
May 15, 2012 at 6:32 am
Hola, bola de reptiles
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Bruce
May 15, 2012 at 11:16 am
Should have said perigee, not apogee, and my last line would have been better as, "A Giant, opposible thumbs down to Thumbing the Moon".
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