‘Supermoon’ this weekend will be biggest full moon of the year

The biggest and brightest full Moon of 2017 is coming this weekend, on Sunday night, Dec. 3rd. It’s a perigee “supermoon,” almost 8% wider and 16% brighter than an average full Moon.

A full moon rises over San Francisco. (Photo: SF Brit/Flickr)

Full moons vary in size because the Moon’s orbit is not a circle, it’s an ellipse:

One side of the Moon’s orbit, called “perigee,” is 50,000 km closer to Earth than the other side, “apogee.” This Sunday’s Moon becomes full only 16 hours away from perigee, closer than any other full Moon of 2017.

How super will it actually look? A 16% difference in brightness can easily be masked by clouds or the glare of urban lights. Also, there are no rulers floating in the sky to measure lunar diameters. Hanging high overhead with no reference points to provide a sense of scale, one full Moon looks much like any other. To get the most out of Sunday’s lunar apparition, try to catch the Moon just as it is rising or setting. This will activate the Moon Illusion and make the perigee Moon of Dec. 3rd look super, indeed. Via (NASA spaceweather.com)

When this month’s full moon arrives, it will perform an optical illusion that has baffled onlookers since Aristotle. As with many moonrises — but especially full moons — it will look bizarrely large when it’s near the horizon, then seem to shrink as it ascends.

This is the “moon illusion,” and it’s all in your head. The moon isn’t changing sizes, and while its distance from Earth does change slightly over time — producing an occasional “supermoon,” which really does appear up to 14 percent larger than usual — that happens too slowly to yield such a dramatic transformation in one night.

More here: http://www.mnn.com/earth-matters/space/blogs/why-nobody-can-explain-the-moon-illusion

58 thoughts on “‘Supermoon’ this weekend will be biggest full moon of the year

  1. Next on climate alarmism: “CO2 is pulling the Moon closer to Earth, collision imminent”

    • Or “Evil capitalist Trump offends Gaia by rejecting Paris Accords, causes moon to threaten Earth”

    • Sadly the moon is inching ever farther away from earth every year, about 1.5″/year actually. Imagine an Earth without tides.

      • rocketscientist
        December 1, 2017 at 9:48 pm

        It’s worse than you thought…eventually an Earth without total solar eclipses. Then there will be none visible anywhere in our solar system ever again. Now that’s sad!

      • @alastair

        It is obviously our fault. Everything is our fault. Probably the extra mass left behind by the Apollo guys.

        /s for the terminally litteral.

      • I saw a report the other day that said the Moon may eventually reverse its departure from Earth and will start spiraling back in until it eventually breaks up and crashes into the Earth in the far future.

      • I believe that the moon was only about thirty feet above the Earth at the end of th4e Cretaceous.
        This accounted for the extinction of the dinosaurs.
        The tall ones, at least!

        [It’s an old one, indeed, well-whiskered, I know . . . .]

      • w/o the moon, Earth would’ve had climate destabilizing obliquity excursions to +45 deg. That would have likely prevented evolution of multicellualr life on Earth.

  2. What?! Another one already? I swear it seems like we’re having a supermoon every other full moon. It must be this decade’s fad … getting excited about the latest supermoon. Well, at least it’s not another polar vortex; oh wait, that’s coming next week … I forgot. sigh . That’s what happens when journalists discover new bits of science they didn’t know about before. They can’t wait to splash it all over the place every chance they get. Well, next decade they can get pumped about something new.

    • Leon Brozyna
      December 1, 2017 at 7:55 pm

      Yes, it’s an interesting trend. Everything slightly different has to become exciting and unusual.

      Slightly larger full Moons become Supermoons, slightly higher tides become King Tides, weather becomes Climate Change, big storms become Superstorms. As someone pointed out recently on WUWT the concept of naming storms or cyclones makes them more memorable and thus unusual. It’s worse (bigger, brighter, stronger, higher) than we thought!

      I think it may in part be related in the rise of social media…every event you see and can tweet has to become bigger and better than your Facebook friends have seen. You have to be the first to report it. The other part is the general lack of knowledge of science and thus how the world and universe work…all by themselves.

      • I noticed that some weather people went all ga-ga over this. The last time I tried to see the supermoon, it was a cloudy end to the day. The sun set behind me and about 45 other people, all of us on the shores of Lake Michigan with cameras to record this stupendous event, and the eastern horizon was thick with clouds. There was a 3-second moment when a hole appeared in one cloud, then it was gone.
        Well, there were no mosquitoes, but the media hype was ridiculous. Speculation arose about whether or not it would produce major storms. One reporter “named” it Steve, or something like that. Supermoon Steve.
        They also name snow storms, you know. We owe it to public sanity to get them to stop naming things.

      • Sara: The criteria for naming a winter storm are: warning thresholds for population (2,000,000) and area (400,000 square kilometers, or 248,548 square miles).
        By my calculations, virtually every large storm on the East Coast qualifies, storms north of Denver, Colorado will never be named, and the West coast will have some named storms. Not a very good criteria there. Of course, people north of Denver know what snow is and how to deal with it. Naming storms appears to be for people who cannot remember what snow looks like year to year and cannot deal with the reality of weather. It speaks to how foolish and unprepared Americans are for weather (or the belief of the forecasters that people can’t plan ahead or understand weather).

      • The “moon at perigee and opposition” is not an unusual nor unprecedented and the immediate effects are called, perigean tides.
        They have existed sine the moon existed. And, since the moon is, and always has been, drifting further away from the earth every year the tidal effects have always been diminishing. So, if the previous more intense tides did not cause “super storms” one may assume that a diminishing force would not either.
        The suggestion that the minor contribution is causing super storms is laughable.
        They could inopportunely add their few more inches of tide to an already unfortunate storm condition, but they most assuredly did not cause the storm.

      • Sheri said:

        Sara: The criteria for naming a winter storm are: warning thresholds for population (2,000,000) and area (400,000 square kilometers, or 248,548 square miles).
        By my calculations,

        By my calculations (okay, my system’s calculations):

        $ units
        You have: 40000 km^2
        You want: mi^2
                * 15444.086
                / 6.4749703e-05

        It looks like you divided by mi/km instead of (mi/km)^2:

        $ python
        >>> 400000/1.6
        >>> 400000/2.56
      • It is most likely exciting to most modern urbanites who rarely even see the Moon. In the past all humans had daily experiences with the Moon overhead every night, it was a constant companion.

  3. Also do not forget that the Earth And Moon orbit the Barycenter of their gravitational fields. The Barycenter is about some 2000 km deep in Earth mantle! The Earth while spinning on its axis is in a very tight orbit around the Barycenter.

    • What a crappy video. It doesn’t say that most of the video is not to scale, with the object appearing much closer than the other. That would also result in the barycenter being much closer to the center of the Earth, something that the video never admits to.

      And the barycenter has no real effect on the forces that drive earthquakes. Tidal forces are real and may be strong enough to trigger some quakes a very small time earlier.

      The barycenter is just a mathematical concept. It has no mass of its own, no gravitational field, it just gets people excited over a cute concept that has little scientific bearing.

  4. Can also be compared to the Micro Full Moon.
    Super – – – 30% brighter, and 13% larger

    “Bigger and larger” seem to be area measurements rather than diameter (across), although what I find does not say so.

    • The “larger” results in a an apparent increase in diameter of only 6% (sqrt(1.13)-1)
      while the brighter is an distance cubed ratio.

    • LOL! What was the latest prediction?

      Because Mt. Pinatubo decreased the entire Earth’s mantle by 4 degrees C don’tchaknow (Yes I have actually HEARD that ridiculous statement before–have fun with that one…HEE HEE).

      • Well Al Gore did claim the Earth’s core is million of degrees. So take that on his science authority.

      • joelo
        Did I miss the – obvious? – /Snarc suffix.
        Or is that SO obvious?
        [Here, yes, I think it probably is; Gore-balls warming and science go together like kerb-stones and rancid cheese].


  5. 16% brighter than an average Full Moon? This can be hardly noticed because, when you look at the Moon, you have no “average” Full Moon in the neighborhood to make a comparison.
    Moreover, how has this 16% been calculated? Based on the distance alone? In fact, at the instant of Full Moon this December 3, the Moon will be 4.6 degrees south of the ecliptic, so there will be a slight phase. The Moon’s disk will not be exactly 100% illuminated. Even if this cannot be seen with the naked eye, the phase effect will have as a consquence that it will drop the Moon’s brightness by several percents.

    • Jean, no doubt the increase was calculated from the reduced distance and not from actual orbital positioning and all the other exactitudes that actually do make a difference, such as the Earth’s gravity is not uniform and cause orbital fluctuations in near earth satellites. The average Joe doesn’t know the difference, and attempting to educate them on the finer points is often lost effort.
      But, if we can get them to understand that things seem brighter when they are closer, perhaps we can proclaim success. And, if some more of them learn that orbits are rarely circular, even better.

    • What is the average phase of the full Moon? Is the Moon at its brightest only during a total Lunar eclipse?

      • “Is the Moon at its brightest only during a total lunar eclipse?”
        That would indeed be the case if the Earth was not there to block the sunlight reaching the Moon.
        Actually, a Full Moon is at its brightest, all other factors being equal, when at a lunar eclipse the Moon has its external contacts with the Earth’s penumbra; that is, at the very beginning and end of the eclipse. At those instants, the angular distance between the Moon’s center and the anti-sun is about 1.5 degrees. This is much smaller than the 4.6 degrees mentioned in my text.

    • Some scientists use an ancient scientific trick known as measurement. I realize it is much less in vogue during the modern era where computer modelling is more the rage.

  6. “When this month’s full moon arrives, it will perform an optical illusion that has baffled onlookers since Aristotle. As with many moonrises — but especially full moons — it will look bizarrely large when it’s near the horizon, then seem to shrink as it ascends.”

    After following the link, this seems easy to me. At that link is a picture that simulates a 3D railroad track that heads off into the screen (paper) and two vertical lines of identical width at different “distances” along the track. Your mind thinks that the “further” line is wider because this perspective makes it look wider than the track, when the same track is wider than the “near” line.

    The same thing happens when you look at the moon proximate the horizon. Everything on the ground gets smaller and smaller as you look to the horizon (true even if you’re at sea). Yet the moon’s distance from the horizon dwarfs your distance to the horizon, so the moon looks no larger from where you are standing than if you were actually standing at the horizon (on a flat plane). But your mind still associates the moon’s size with what it thinks should be the reduction in size based on a distance from you to the horizon.

    • Kurt – December 2, 2017 at 12:21 am

      But your mind still associates the moon’s size with what it thinks should be the reduction in size based on a distance from you to the horizon.

      (something to think about, to wit:)

      And just how is it possible for “your mind” to perform the aforesaid “reduction in size” …… unless one’s mind consists of two (2) distinctly different entities, ……. (1) the subconscious mind that performs said reduction as it composes the “image” ……. and (2) the subservient conscious mind that is made aware of or informed about the resulting reduction in/of said “image”?

  7. I shall watch the tide in my local harbour with interest. I can see the tide in harbour even when it is cloudy. Which seems to be the norm these days.

    • Amazing! Mass of moon exerts huge forces on fluid pulling it this way and that.

      Apparently it also affects the water on the surface too.

  8. If it’s slightly closer, will it have an effect on the Great Lakes? They all respond to the Moon’s influence, y’know. Bigger waves, maybe?

    It might have an effect on your hair, too. Good day to cut your hair if you want to thicken it. If you want to strengthen it, wait until January 1st/2nd.

  9. I once worked with someone who claimed that if you dug a post/pole hole on a full moon and set the pole or fence post in it there would not be enough soil to fill in the hole even with the pole in it. Opposite effect on a new moon (you would have to remove excess soil). It’s been a long time ago so the effect may have been reversed between the stages of the moon. You gotta plant your posts in the correct phase of the moon.

  10. When the heck did a “harvest moon and planters moon” become a “Supermoon”?

    Nothing new to see here folks….move along.

    “Baffled Aristotle?” Seriously? Did anyone ask? No? Then how did they know? I seem to recall from basic Physics that the optical illusion was first broken down by ancient astronomers(don’t roast me, I can’t recall who it was)..correct me if I’m wrong but wouldn’t Aristotle have studied them too?

  11. Jean Meeus December 1, 2017 at 11:26 pm
    “at the instant of Full Moon this December 3, the Moon will be 4.6 degrees south of the ecliptic,”

    An additional factor, rarely reported, is that that “instant of full moon” is not on the evening of Dec. 3 for many locations. For those of us on the U.S. west coast, the moment of fullest moon is 7:47 am PST. That means the moon will be equally full at 7:47 pm on Dec. 2 as it will be at 7:47 pm on Dec. 3. The moon will actually be fuller if I view it at any later time tonight than it will be tomorrow night at that same time.

    The difference in brightness being hyped is rarely what it’s cracked up to be.


  12. Although I appreciate the effort to get people interested in backyard astronomy…

    …the “supermoon” is a meaningless attraction. Nobody could ever tell you that a particular moon was bigger or brighter, because the changes are so subtle.

    Also, the largeness of the moon has nothing to do with a slightly closer proximity. EVERY full moon, or even a moon a few days either side of full, looks huge upon sunrise and sunset. This one is no different in that regard.

    • But… the difference displayed in the photograph is not the difference between an average month, and this month, nor the difference between last month, when no comment was made, and this month. The two images represent the moon as it appeared years apart. The changes in apparent size of the full moon are gradual, whereas the coincidence of a particular night’s weather makes a much greater difference. It is a case of much ado about very little. Except for the hubbub, no one would notice. It is exactly like a marketing ploy. Is some one trying to increase magazine sales?


  13. The moon looked pretty darn good tonight, already. Very bright outside.

    At least when the full moon washes the star away from visibility it still leaves a pretty sky.

  14. The moon was always uniformly small.
    Then along came global warming.
    The CO2 horsesh*t has to stop.

  15. Wow: You say that the moon tonight will be slightly less than 8% wider than the average full moon. That implies that this full moon might be roughly 16% wider than a mini-full-moon. So, since area is related to radius (diameter) squared, the mini-full-moon will be 1 – 0.84×0.84 = 0.705, roughly. This means that the mini-full-moon would be about 30 percent less bright than tonight’s moon!

  16. Alastair Brickell December 1, 2017 at 9:59 pm said

    “It’s worse than you thought…eventually an Earth without total solar eclipses. Then there will be none visible anywhere in our solar system ever again. Now that’s sad!”

    Actually not sad as where will always be total solar eclipses, just not from earth. Everytime there is a lunar eclipse, an observer on the moon would have a total solar eclipse. Just as they could have an annular eclipse of the sun. And of course, observers on any of Jupiter’s or Saturn’s moons would have a total solar eclipse every few days or so.

    I thank JBom December 1, 2017 at 8:06 pm for the link to a bad video, and after having watched it, I found a link to an even worse video by someone who had no idea what he was talking about. Try viewing https://www.youtube.com/watch?v=3cJ3AemeUFM and look at his diagram with earth and moon represented as cars going around the race track around the sun. Remember that the close to the sun, the faster a satellite will go. But he has it going slower, which is impossible. Yuck! No wonder he gets the shape of the moon’s orbit wrong. In fact, the moon’s orbit is always concave towards the sun – hence it is more proper to say that the moon and earth are a double planet in the same orbit, similar of a pair of Saturn’s moons.

  17. Today’s science does not know the exact appearance of the celestial bodies. Two celestial bodies (Earth-moon, or this pair and the sun) move together under the influence of the Newtonian Force, mutually alternate the potential and kinetic energy in relation to their centers of mass.
    So Earth and Moon have their own center of mass –
    Both bodies roam around that center, but not according to Kepler’s laws. A certain amount of kinetic energy of radial velocity converts the convergence of two vectors (two spins of the same size, and the opposite directions). One spin is its own, and the other is the rotation of the body around the center of mass on a sinusoidal radius.
    That’s why the moon has always one and the same side facing the Earth.
    The proof that the moon is not rotating around the Earth is the fatamorgana of that “thinker.

Comments are closed.