Sciency Words: Supermoon

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we talk about the definitions and etymologies of science or science-related terms.  Today’s Sciency Word is:

SUPERMOON

I was recently part of a comment thread over on Scott’s Sky Watch.  We were talking about the term supermoon, along with other weird moon names like wolf moon, blood moon, harvest moon, corndog moon, flower power moon, gingivitis moon… you get the idea.  After that, I thought a Sciency Words post on “supermoon” was in order.

The term supermoon was coined by American astrologer (repeat: astrologer, not astronomer) Richard Nolle.  The term first appeared in an article Nolle wrote in 1979 for Horoscope magazine.  To quote Nolle himself from this 2011 webpage article, the term supermoon describes:

[…] a new or full moon which occurs with the Moon at or near (within 90% of) its closest approach to Earth in a given orbit.  In short, Earth, Moon and Sun are in a line, with Moon in its nearest approach to Earth.

This particular alignment of the Sun, Moon, and Earth is also known as a syzygy-perigee.  Perigee means the point when as object orbiting Earth comes closest to Earth, and syzygy refers to the straight line alignment of three celestial objects.

A syzygy-perigee has a marginal effect on Earth’s tides, and if the Sun and Moon are on opposite sides of the Earth (as depicted in the highly technical diagram below), then the Moon will appear to be slightly larger and slightly brighter than normal in our night sky.  Astrologers would have more to say about supermoons, but from an astronomy perspective we’re pretty much done here.

Personally, I don’t really have a problem with the term supermoon.  When the full moon or new moon happens to be 90% closer to Earth than usual, that’s kind of neat.  Sure, the term started as an astrology thing, but there’s a long history of astrology concepts and terminology being borrowed by astronomers.  Supermoon is no different.

And supermoons do tend to get a lot of attention in the popular press.  I’ve had a lot of awesome conversations with people about the Moon and space and science in general that started because of a news report about the latest supermoon.  I think that’s great.  Anything that gets people to take an interest in science is a positive thing in my book.

On the other hand, a few of those conversations have ended with people asking me about their horoscopes, which is a bit disappointing.

Next time on Planet Pailly, please don’t hate anybody, not even the people who deserve it.