Was it a Blue Moon, Blood Moon, Supermoon?

So, the Full Moon of January 31 was red, white, and blue?  A Blood Moon because it went into eclipse in the Earth’s reddened shadow.  White because, as a Full Moon, it glared white on either side of the eclipse.  And  blue because it was the second Full Moon in the month.  And it loomed large toward us, a Supermoon!

How much of that is true?

If you were where the total eclipse could be seen, let us know how reddened the shadow on the Moon became on this occasion.  Reports so far suggest it was only slightly tinged.

As for being a Blue Moon, that has two or more meanings.  I’ve put my full explanation into a new “Moon” section of “Astronomical Calendar 2018,” to which you can get by clicking that tab at the top.  Briefly, it was not a Blue Moon in the older sense of being a fourth Full Moon in a season; but it was, in the later and now more widely-known sense of being a second Full Moon in a calendar month.  March, too, will have two Full Moons, the second being “blue” in this sense, because the month in between, February, has no Full Moon at all.

And was it a Supermoon, looming outstandingly large because of being exceptionally near?  No.  It was the fourth nearest Moon of 2018.  The nearest was its immediate predecessor, the Full Moon of January 2.  That occurred only about four and a half hours after a perigee, or nearest moment in the Moon’s orbit; so the Earth-Moon distance (between their centers) became as small as 55.91 Earth-radii.  The Jan. 31 Full Moon occurred nearly 28 hours after a perigee, so the distance reached 56.28.  Small, but by no means the smallest.

This graph, which has also been put into “Astronomical Calendar 2018,” can make things clear.

The curve is the Moon’s distance.  The circles are the Moon – to scale – at its Full, Last Quarter, New, and First Quarter moments.  The distance varies over each lunar month, between perigee (minimum) and apogee (maximum).  But these extremes vary in a larger wave taking somewhat less than a year.  Especially the perigees, which this year are nearest-in around January (near Full Moon moments) and July-August (near New Moons).  So the Moon is near around the Jan. 2 and Jan. 31 Full and July 13 and Aug. 11 New times, but the nearest is the Jan. 2 one. It happens to be the only one of the four at which an eclipse does not occur.

Newspapers showed gorgeous “Supermoon” photos from around the world, giving the impression that the Moon got stuck between skyscrapers or that cyclists on a hilltop could reach out and touch it.   Such photos may bebetter suited for illustrating  the “Moon Illusion,” whereby the Moon when near the horizon appears larger to the mind than it geometrically does to the eye.  But their trick is narrow angle of view, so that something distant and small seems huge when a small piece of foreground is superimposed on it.

I’ve also put into “Astronomical Calendar 2018” the beginning of a section about eclipses.



13 thoughts on “Was it a Blue Moon, Blood Moon, Supermoon?”

    1. Maybe someone has given the title “blood moon” to a sequence of four total lunar eclipses. As far as I knew it was just a popularizing term for a lunar eclipse that goes markedly red.

      Jean Meeus in one of his five “Mathematical Astronomy Morsels” books has, I’m pretty sure I remember, an analysis of when and how sequences of four total lunar eclipses occur. You could find it by searching in the cumulative indeix in the last volume.

  1. The definition of a blue moon as the third of four full moons in a season accords with the expression I grew up with in South Carolina: “Once in a blue moon!” It was utilized to give expression to events that were known to happen but not often, usually years apart, and multiple times in the life-experience of the speaker. See here: https://www.obliquity.com/astro/blue-seasonal.html

    In this manner, “once in a blue moon” occurred far more frequently than “when hell freezes over.” The latter was used by the speaker to suggest, “never!” With my book learning on display, I can say that Lake Cocytus will never flood and freeze to Hell Gate, therefore, “when Hell freezes over” does mean “never!” See here: http://dantesinferno.wikia.com/wiki/Lake_Cocytus

    Frankly, I am at a loss with how to utilize the new-fangled calendrical blue moon as a time equivalent from my long ago youth and its memorable units of time.

    1. I give a paragraph to “once in a blue moon” in Astronomical Calendar 2018: Moon. I too heard the phrase in childhood.

      It means “rarely”, and “usually years apart”, as David says. “When hell freezes over” means “never” or at least “not till the end of the world”. The most delightful expression for that was uttered by Nikita Khruschchev: he was saying, I think, that if the West wanted to wait till the Soviet Union submitted to something or other, it would have to wait “till shrimps learn to whistle”.

      I don’t know whether he coined it or, more probably, it was a Russian folk-saying. I get fun from remembering Comrade Khrushchev for that, for his emphasis of some other point by taking his shoe off and banging it on a table, and from the German transcription of his name: Chruschtschew .

      1. You must love the thought that Putin’s name comes out Poutine in French, poutine being a Quebec invention involving French fries and curd cheese drowned in gloppy brown gravy. I’ve never dared try it for fear I’d get hooked and soon weigh 300 lb.

  2. I look at the Moon every clear night and day (and the partly cloudy ones, too), in every phase (except new!) and at every distance, whether or not there has been recent media lunacy. The 31 January full Moon was a noticeably bigger and brighter than an average full Moon (as was the 2 January full Moon). The slightly greater proximity of the July and August new Moons to Earth will have an effect on the tides, but not on lunar observation. Nobody looks at the new Moon. If we’re going to start using “super Moon” to describe close Moons, this one qualified.

    I observed the lunar eclipse from San Francisco, with totality from 0451 to 0608 Pacific Daylight Time. Mid-eclipse was at 0530, astronomical dawn at 0545. While crossing the edge of the Earth’s umbra the Moon’s surface appeared deep red. Everything inside the edge appeared dark grey to me. I would call this L1 on the Danjon scale.

    A photo taken by a member of my astronomy club 20 miles north of here shows a partially eclipsed Moon that shades from grey, through a brighter red than I saw, to a very subtle purple umbral edge that I didn’t see at all. I don’t know how much of the discrepancy is due to the greater color sensitivity of a CMOS chip and how much is due to processing.

    1. Please look at the new moon! “The old moon in the new moon’s arms” is a glorious sight, and finding the silver sliver as soon as possible every lunar month has turned into a family pastime and a great excuse for an early evening stroll.

      1. (I meant “newish”, of course. My brain has been warped by “The Ballad of Sir Patrick Spens” (q.v.).

        1. Ah, we’ve stumbled upon another ambiguity in lunar terminology. You’re using the more traditional meaning of “new Moon”, the first view of the thin lunar crescent in a lunar month. Indeed I do go out of my way to see thin crescent Moons. I was using the term in its more contemporary astronomical sense, i.e. the moment when the Moon passes closest to the Sun in the sky. (Guy has pointed out this distinction somewhere.)

          By the way, an amateur astrophotographer (Thierry Ligault, if memory serves) took a picture of the new Moon (in the strict astronomical sense) during a month when the new Moon happened to pass farthest south (or north?) of the ecliptic, so there were a few degrees of separation between the Sun and the Moon. Sort of the opposite of a solar eclipse.

  3. I’m glad media draws our attention to astronomical events, but I think they tend to overdo some it. Blue moons are more or less a creation of our own as we devise our calendars. Next one ‘ll be in March and Feb has no full moon at all. I’m still waiting on reports from friends on the west coast and on Maui fpr this most recent one. . My friend from Maui was whom I visited for the second of the transits of Venus. A partial lunar eclipse occured a few nights before, but he wasn’t that enthused by it. Stlll got my calendar marked for the next total eclipse of the sun in April, 2024. Upstate NY looks like the best so far. locally near and a glimpse of Niagara Falls would make it a nice road trip.

  4. I’ve never been happy with lumping “blue moon”, which depends on the vagaries of our calendar, with a real astronomical phenomenon like perigee.

    1. But in order to garner media attention, a celestial event needs to be sensational! I’ve lost count of all the once-in-a-lifetime events I’ve read about in the local newspaper.

      1. I agree. Especially with these supermoons. Comparing a full moon at perigee and apogee is similar to comparing a U.S. quarter and nickel. You can easily tell the difference if you put the two coins next to each other. But if you showed the average person the full moon fairly high in the sky (to avoid the moon illusion) near perigee and again near apogee and they had no idea if there was a supermoon today, I doubt most of these people would be able to tell the difference. I never even heard the term supermoon until well after the internet and social media were mainstream. I believe this supermoon hype just gives people something to talk and brag about in social media.

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