Supermoon Summer: Not much new to see here but check it out anyway
Did you know it was Supermoon Summer?
There’s a mini-moon, a blue-moon, a harvest-moon and so on. So what’s a supermoon?
Well, it’s one of those cosmic coincidences that humans like to point out but, in this case, isn’t that dramatic. The science behind it is pretty cool though.
A supermoon is not where superman’s fortress of solitude is (I think). It occurs when a full moon takes place around the time of it’s closest approach to earth and it’s happening now. We also had one in July and the third occurs this September but the best one of 2014 is now though.
Yes, the moon’s distance from earth varies in the course of its monthly trip around earth. This is because it has an elliptical orbit instead of a circular one. This causes its distance from earth to vary from around 225,000 miles to 250,000 miles. As a result, its apparent diameter is about 8% larger than an average full moon with a concomitant brightness increase of about 30%. This also makes it about 15% bigger than the smallest the moon can appear.
The term supermoon is not generally appreciated by astronomers. It came from a 1979 astrology publication (yuck) but has become increasingly popular since then. They prefer more geeky and less sensationalistic terms like “perigee full moon” or “proxigean moon”. You may come across the term perigee a lot if you look into this phenomenon. That simply means “closest approach”, opposed to apogee which is the opposite. To remember the difference between these terms, I imagine putting my face real close to a periscope in a submarine. That mental image of my eye close to a periscope still pops up whenever think of the word perigee even after 20 years or so.
The bottom line about this supermoon is not to get your hopes up too high…or perhaps up at all. Only the most eagle-eyed among us will notice much of a difference if even at all. You’d think that 30% increase in brightness would be impressive but even that is highly variable due to haze and cloud cover. Also, the peak size and brightness was Sunday August 10th but the next couple nights will be little different.
If you do go looking for it you may want to find the moon on the horizon. The “moon illusion” makes this extra enjoyable even for “plain” old normal full moons. This illusion is a psychological phenomenon in which the moon on the horizon appears bigger due to its proximity to foreground objects like houses and trees (that’s one of the theories anyways).
The major downside to this month’s supermoon though is that it occurs during one of the best annual meteor showers, the Perseids. Full moons greatly attenuate meteor displays though some of the biggest streaks will still be visible. I’m not too disappointed though because for the past 15 years (literally) there has always been something that totally ruins the Perseids for me, so I’m kinda used to it and don’t cry any more (much).
If it’s gotta be something, it may as well be a Supermoon.
Image Credit: Marco Langbroek, the Netherlands, using a Canon EOS 450D + Carl Zeiss Jena Sonnar MC 180mm lens.