The Half-Astrophysicist Blog

Super Moon and Mini-Moon

On March 19th, lots of people heard about the so-called Super Moon.  The Super Moon was a full Moon that occurred when the Moon was closest to Earth in its elliptical orbit. Therefore, it appeared slightly larger and brighter in the night sky. The difference is small enough that most people would probably have trouble telling the difference without visual aid (I know lots of people said they could, but how many of them look at the Moon on a regular enough basis to judge? I would love to start a rumor that some random month had a super Moon and watch everyone claim it looks so much bigger but that’s another story!)

Tonight is the smallest full Moon of the year which I have dubbed Mini-Moon for lack of  a better term.  The Moon near the farthest point in its orbit on the evening of full Moon. Again, it’s not much smaller and you probably have a hard time telling the difference without visual aid.

Now I used visual aid in the form of a Canon Digital Rebel Xti and a 70-300mm zoom lens (at 300mm of course). I took a pic back on March 19th and another one just now.  Not much has been done to them and they didn’t come out as well as I had hoped, but the size is clearly different.

These are at the same scale of course.  You can clearly see the March 19th pic (left) shows a larger Moon than tonight’s photo (right). You don’t need a lot of expensive equipment to do this type of photography.  Many people have cameras similar to mine with comparable zoom lenses.

You can do the same with the Sun if you have a solar filter. Earth is closest to the Sun in early January and farthest from the Sun in early July.  I think I will get some solar filter material and make that a 2012 project!

October 12, 2011 - Posted by | Astrophotography, Moon, Solar System


  1. The experiment has actually been done – by me, inadvertedly, in February, when I noted that the full moon (high in the sky, i.e. no moon illusion at work) looked unusually large: only then did I check the ephemeris and found out that it was close to perigee, practically a match to the March situation. Same happened in October when I noticed the full moon being unusally small, and indeed the situation nearly resembled today’s apogee.

    It’s a pity that so many bloggers are telling people that “you can’t see it, and if you think you can, it’s because you read about it on the web” when the ellipticity of the Moon’s orbit is actually a fundamental astronomical observation everyone – who actually steps away from the computer and looks up! – can do himself; the effect is actually pretty striking …

    Comment by Daniel Fischer | October 12, 2011 | Reply

  2. I did not say you couldn’t see the difference. I said most people would have trouble without visual aid. The difference between the largest and smallest full Moon is a touch under five arc seconds. The resolution of the average human eye is about 1 arc second. So yes, a very observant person could tell. However, there are few reference points in the sky to accurately compare the size of the Moon which makes it more difficult (and of course the difference in size is overwhelmed by the famous Full Moon Illusion when it is near the horizon).

    Maybe I should post the two full res versions of the pics, uncropped and unlabeled. You have to look pretty close to tell the difference and I used a zoom lens so it is magnified.

    Comment by halfastro | October 12, 2011 | Reply

  3. You mean arc minutes: It’s 34.3 vs. 29.5 arc min for average perigee vs. apogee, i.e. the apogee moon is 15% larger in diameter or 35% (a third!) larger in area. That’s what you notice: To the attentive naked-eye observer the bigger and also brighter disk is quite an effect. (I wouldn’t have believed that myself though if I had not ‘discovered’ perigee at the February full moon – and tonight’s was significantly smaller than how I remembered the winter/spring perigee full moons.) See also this composite from July 2011 when peri- and apogee coincided with the first and last quarter: no labels needed …

    Comment by skyweek | October 12, 2011 | Reply

  4. D’oh! Arc minutes of course!

    And you should remember that not everyone spends a lot of time carefully observing the Moon! Experienced observers no doubt would have an easier time telling the difference.

    Comment by halfastro | October 13, 2011 | Reply

  5. […] Super Moon and Mini-Moon On March 19th, lots of people heard about the so-called Super Moon.  The Super Moon was a full Moon that occurred when the Moon was closest to Earth in its elliptical orbit. Therefore, it appeared … […]

    Pingback by How super is a super moon? | DavePlus | June 23, 2013 | Reply

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