May 28, 2020

AstroEvent: An Equinox, a Full Moon, and a Perigee.

NOTE: The post that follows was written and loaded for timed release before the March 11th earthquake & resulting tsunami  off of the coast of Japan. We decided to release it early to combat much of the pseudo-science that was already afoot about the “Super-Moon…” To re-iterate much of what follows, perigee is perigee, and varies little (<4.5%) from lunation to lunation.  Astronomers are not predicting earthquakes, Nibiru, or Sheen-zombie apocalypse as a result of an apsidal Full Moon…

A perfect storm of astronomical events is transpiring at the end of the week, one that will no doubt trigger the worldwide Woo and break with much shoddily composed pseudo-science journalism. But you’ve arrived here at Astroguyz in search of astronomical knowledge, so we’ll give you the straight up-low down on the street;

The action starts March 19th, with the closest Full Moon of the Year. The March Full Moon is also known as the Full Worm (or do you say Crust, Sap, Crow, or Lenten?) Moon, and will appear 34’ in size as opposed to its 29.3’ appearance near apogee. This is because lunar perigee occurs only an hour later, at 19:10 UT. This perigee is also a particularly close one of 356,577 kilometers, nearly the closest it can occur. Don’t forget, solar drag occurs on the orbit of the Moon, adding to make its orbit quite complex. Still not enough? The vernal or spring equinox occurs about 28 hours later, on March 20th at 23:21 UT. Everyone has approximately 12 hours of equal darkness and daylight around this date, regardless of latitude. (You did remember to “spring” forward yesterday, right?) The Full Moon is currently sitting very near the direction that sun will appear to be during the autumnal equinox later this year.

How rare is a lunar perigee within an hour of a Full Moon? Reader and human astronomical computer extra-ordinare Ed Kotapish ran the numbers and came out with only three other notables from 1960 to 2060 AD:



PROX  NOV     20     1972     2306      -0.9     356528
PROX  JAN      19     1992      2128      -0.7     356550
PROX  MAR     19     2011      1810      -1.0     356580
PROX  MAY     06    2012     0335      -0.0     356954

Note the last time that this occured was January 1992, and next year’s will be even closer timewise…the negative number denotes the time in hours that perigee occurs after the instance of the Full Moon. (Thanks, Ed!)

…Which leads us into the astro-term for this week, which is a Proxigean Tide. This type of unusually high tide occurs when the first two conditions above are met, namely a Full or New Moon very near perigee. Proxigean Tides are not that unusual, as one occurred during the January 2010 Full Moon and one will happen during the May 2012 Full Moon. These do not have to occur during the vernal equinox, but it’s a triple cool coincidence when it does. The very term Spring Tide actually has nothing to do with the season of the same name, just the “spring” or surge in tide levels directly after a New or Full Moon as opposed to the lull or “neap” tides preceding the same. Despite what Bill O’Reilly will tell you, astronomers have a pretty good handle on what causes the tides (we had to go there!)

What’s a little murkier is the precise effect the Moon has on tectonic plates on the Earth. Yes, there are measureable land tides, and much hoopla has been made as of late of a link between earthquakes and the Moon. An infamous prediction was supposedly made of last month’s New Zealand earthquake in this fashion, although that while stating an earthquake will occur within two weeks of a New or Full Moon may be a very safe bet, but is neither accurate nor precise as per Science 101. (What were the Vegas odds, like 1:1?) Fact is, we cannot unequivocally state “This earthquake is related to that Full Moon,” any more than we can state “This hurricane is directly linked to global warming” as one is a single event in an overall trend. Predict enough earthquakes near a particular lunar phase, and a few are bound to occur; and yes, we know of the Taiwanese study a few decades back that suggested a weak statistical link; interesting, but the USGS and most scientists still remain unconvinced. I wouldn’t make my travel plans around it as some are in fact doing… laugh at the fuss that’s bound to occur, but do get out in enjoy the largest Full Moon of the year this weekend, and an especially high tide and the beginning of northern hemisphere spring to boot!


  1. Ed Kotapish says:


    Don’t forget to menntion that the time given is for the Full Moon and negative numbers are after.

  2. Tara says:

    Interesting. At first I wondered if the upcoming perigee moon could have caused the earthquake in Japan, but scientists are saying it did not since it was not close enough to have caused it.

    I’m hoping for a clear night on the 19th!

  3. nica says:

    I’ve been noticing what the moon is doing and the effect it has on me for nearly two decades, mostly to do with natural fertility. The week before the Sept 4 earthquake in Christchurch, I noticed that the moon felt particularly “strong.” I dont know why. I just noticed what it feels like to me. The week before the Feb 22 earthquake, I joked about it being a “bad moon arising”. I was a little embarrassed to call it that, as I dont believe in “bad moons”. But I did think something was going on. Being in Christchurch when our largest natural disaster happened and seeing people die, unbelievably, in a safe city, it was hard not to think back to the week before. Of course this is not scientific, except in that I observe in a dispassionate kind of way what I feel like in Nor wests or full moons. And thats what I felt.

  4. Nima says:

    How does the shifting tilt of the axis effect the time of vernal equinox this year? or in the years ahead (near or mid-range future, say 5 to 10 years, if no other similar event takes place)?
    18:21 EST this year… how many seconds will change over time?

  5. David Dickinson says:

    Because our year is not precisely 365 days long (its about an extra .25 days over) the equinox creeps up about 6 hours each year, between 0600 UT on Mar20th through early on the 21st before the leap year such as next year resets it. The extra accumultion isn’t extactly .25 either, which is why the Gregorian calendar has provisions to skip leap years every century year, except for years divisible by 400 such as happened in 2000. Such is the complex motion of our world. Over further time scales, the 26,000 year precession of the equinoxes moves the equinoctal points around the ecliptic, then there’s the even longer periods known as Milankovitch cycles, but that a whole other post!

  6. CHermione1 says:

    It is HUGE and clear and white and detailed and amazing!! One hour away from Baltimore. Amazing! Never seen one like it before either.

  7. K.R. Holm says:

    I remember seeing a huge yellowish or orangeish moon on the horizon when I was a girl living in Clearwater Florida. I think it might have been 20 November 1972. (the date given above for lunar perigee within an hour of a Full Moon) Can anyone else remember this?

  8. K.R. Holm says:

    I can recall seeing a really huge low on the horizon yellow or orange moon while walking our dog as a girl in Clearwater Florida. I remember being amazed but thinking it was just caused by the weather conditions or something. I think it could have been the 20 November 1972 lunar perigee within an hour of a Full Moon as included above. Can anyone confirm that is what I must have seen?

  9. David Dickinson says:

    Well, I can confirm that the Full Moon was indeed very near perigee on that date: As for the color, sure… I’ve seen the rising Moon appear pink, red, orange…. though never a true ‘blue’ moon.


  1. [...] For those curiously minded readers, the last time there was a Full Moon aligned with the Moons perigee, it was 1992 – January 19 to be exact. In a rare quirk of fate, there is another Full Moon/perigee alignment in 2012 – on May 6. I got these dates from Astro Guyz, who you can read more about here [...]

  2. [...] more than a properly functioning set of eyes. Last year, the Internet was abuzz with tales of the “Super-Moon,” one of the closest perigee Full Moons of the century. Well, this May, we’ll witness one [...]

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