The SuperMoon is Back

I saw it on Facebook first, shared by a family member… The meme that will not die…

SuperMoon Hype
The usual Super Moon hype as found on Facebook, source unknown
SuperMoon is back!

The claims are the usual… The Moon will be huge in the sky. The Moon will be closer than is has been in some huge time span.

There is some truth here, the June full Moon will be a bit bigger and brighter than usual. And it will be closer to the Earth than it has been in a long time, if you consider 27.5 days to be a long time.

The SuperMoon meme exaggerates the truth to varying degrees.

It all relates to lunar apogee and perigee. As the Moon’s orbit is elliptical, it does get a little further and closer during each orbit, but the difference is fairly minor, the distance varies from 405,000km (251,000miles) to 360,000km (223,000miles) from the Earth. This difference in distance results in the Moon appearing up to 12% larger at perigee compared to apogee. For a better explanation you can go to another post that explains this more fully, with graphics.

12% difference, noticeable if you look close, but hardly a “SuperMoon”.

The Moon passes through perigee, the closest point every 27.5 days, about once each orbit. Not a very long time. But SuperMoon only occurs if perigee happens to coincide with full Moon. As these two cycles are usually out of sync with each other people do not usually notice. About once a year the two cycles coincide and we get a slightly larger, brighter full Moon… The SuperMoon. Interesting, but not as dramatic as the hype.

Lunar Apogee & Perigee
The apparent size of the moon as seen at perigee versus apogee
Another theme that pops up in the SuperMoon meme is a prediction for more earthquakes or volcanic eruptions. I found this one again touted in some YouTube video on the June 2013 full Moon. This claim would at least seem to be somewhat logical, lunar tidal forces do have notable effects on the Earth.

Geologists have studied the lunar earthquake/volcano possibility for decades with varying results. Indeed, some older studies seemed to indicate a link. More recent studies have pretty much ruled out any association, better data associated with more instrumentation and improved worldwide coverage has shown that if there is any effect it is quite small.

Besides, if there were a link, the earthquakes should occur every 27.5 days as the Moon passes through perigee, they do not. There is no reason to make anything special of the full Moon/perigee synchronicity.

June 23rd will offer a nice, bright full Moon. A great time to take a moonlit walk, or a night dive. Ignore the scaremongers, and use this as an excuse to enjoy our beautiful universe.

Author: Andrew

An electrical engineer, amateur astronomer, and diver, living and working on the island of Hawaiʻi.

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