-by John Hlynialuk
Having done two previous columns about the so-called "super Moon" coming Dec 3, you probably know all you need to know about them. But just to get all my gentle readers on the same page, here is a quick recap. The Moon's orbital path is an ellipse and so it comes closer to Earth at one point called perigee and farthest at apogee. The phases are not synchronized to perigee or apogee and we get all phases appearing at each point but if full Moon and perigee coincide, astronomers call it a "perigean full Moon". Forty years ago an astrologer called it a "super Moon" and the name caught on. No one pays much attention to the apogean full Moon -"mini Moons" get no respect. Other phases come at perigee too, but no one but amateur astronomers seem to care, it seems, and I have a story to tell about that.
At perigee, the Moon is a bit larger in size but not noticeably "super-sized" and I suspect that it looks bigger because people are experiencing the "Moon Illusion", an optical illusion that makes all objects near the horizon look larger to our eye. It is a eye-brain thing actually, not totally understood, and there are half-a-dozen books of theories about what is going on. Google "Moon Illusion" for some interesting reading, including how to defeat the illusion (turn around, bend over and look at the full Moon through your legs. I have tried it, it works).
You should be ready for the hype to come because the next full Moon (Dec 3) is close to perigee so it will be a media "super Moon". To top it off, using the loose definition of the term, it will be the first of three consecutive super Moons! A strict definition allows for only one super Moon during each 13-month cycle, but for no reason I know of, it is felt that super Moons should be yearly events. In fact, the perigean full Moon of Jan 1, 2018 (not Dec 3, 2017) is the closest (and most super) since the last one thirteen months ago, on Nov 14, 2016.The next three full Moons all fall within the loose definition (90% of the perigee distance) so we get three in a row.
In addition, someone is bound to notice that in January, there are two full Moons in the same month, an example of what is commonly called a "blue moon" month. Media-wise, this will be another field day of "loosey-goosey" information to pass on (the exception being the paper you are reading, of course). Like "super Moon", "blue Moon" is also defined in several different ways, but I will spare you the details, that is a job for Google.
My perigean Moon story happened many years ago, when I took a pair of photos showing Moons not at full phase but at quarter phases. The idea was to be able to compare the sizes of the Moon at perigee and apogee on one 35 mm slide, but my problem was that with my equipment, full Moons were too big to fit side by side on one slide. So I opted for "'half moons" and in the days BP (Before Photoshop) I cut and mounted the separate images onto one cardboard slide frame. It eventually took two years to get the appropriate quarter phases to correspond to apogee and perigee, longer than it should have, but local weather often interfered. A computer scan of the original slide is shown here. The left side shows the last quarter Moon at perigee and the right half shows the first quarter Moon at apogee. The size difference is readily seen.
In conclusion, there is nothing special about getting a full Moon at perigee because that point can correspond to any phase. Furthermore, there is nothing special about getting a second full moon in a month, since with 13 orbits by the Moon around the Earth in a year, there has to be some month which has two full Moons, or two first quarters, or two new moons or whatever phase you want. It just depends on how the cycles mesh up.
So can we please stop talking about "super Moons" and "blue Moons"? They are nothing special. I promise this is the last that you will hear from me about that subject.
Hold the presses! I just checked my calendar of astronomical events for 2018 and discovered that there is a lunar eclipse happening on the full Moon night, Jan 31! I can just see the reports about the "incredible, once-in-a-lifetime eclipsing, blue, super, Moon". Here we go again!
