Complex Numbers

Less Than Super

Today's link, from Atlas Obscura, is now outdated, having languished in my queue for several weeks. It's just as well, because if it'd come up anytime before August 30, it would have led to a rant, and I ranted about that particular subject enough for this year.

    Just How Super Is The Coming Supermoon?  
July’s full moon will be thousands of miles closer to us than usual. Learn how to measure it with your hand.

I'm linking it despite its lack of timeliness, because it's got general information of value to skywatchers. And some dubious information that I, of course, am going to question.

The Moon is growing now, more and more of it visible every evening. Though it is technically full for just one night, it will look mostly full for a night or so before and after that.

Again, not current information. And yet, I'm going to pick on it. It's technically "full" for just one moment, and half the time, that moment occurs during daylight hours wherever you happen to be. Traditionally, in most cultures that observe this sort of thing, a full moon spans three nights.

The term “supermoon” is a relatively recent introduction to the astrological lexicon, but these events are nothing new; they occur several times a year.

Okay, fine, I'm going to rant anyway. "Astrological?"

I'm not even going to legitimize the sentence that follows that quoted one by pasting it here. Suffice it to say it made veins pop out in my forehead with its utter wrongness.

A supermoon takes place when the Moon is nearest to Earth in its elliptical orbit around our planet.

And that happens once per orbit: at perigee. It doesn't always coincide with a full moon. When it does, that's what they've taken to calling a supermoon. I don't object to the terminology here; what I object to is when people draw the wrong conclusions from imprecise language.

The Moon can look about 14 percent bigger during perigee, its closest approach to Earth, than during its apogee, its furthest point. It can appear 30 percent brighter, too. If you pay attention throughout the year, you might notice how much smaller or bigger the Moon can seem from month to month.

Fair enough, though the article starts out by comparing perigee to average, then compares perigee to apogee. Also not mentioned: the horizon moon illusion, where the rising or setting moon might appear larger to the eye. There's a very reasonable explanation for this illusion, and it has nothing to do with earth-moon distance.

Incidentally, the article doesn't do a very good follow-up on its promise in the subheadline, the "measure it with your hand" thing. There might be a way to do this, very roughly, but I suspect that individual differences in things like arm length and hand size overshadow the supermoon/micromoon difference.

Which, admittedly, is one I've never seen. I wouldn't know a particular full moon was a supermoon but for the websites I frequent, which all gush about it every time it happens. I know some people claim to be able to tell the difference, and I don't doubt them, but my perception just isn't that fine-tuned.

I make up for it by insisting upon pedantry.