“Don’t tell me the moon is shining; show me the glint of light on broken glass.” –Anton Chekhov
Ahh, Chekhov, you old sour puss, what do you have against the brilliance of our Moon?
Beautiful in our sky, the Moon typically takes up half-a-degree in the night sky, where it’s by far the largest and brightest object visible to the naked eye (well, for those of you who can’t see the full Andromeda galaxy with your naked eye). But the Moon actually varies in its apparent size in the sky! If you photograph the Moon when it appears to be at its largest, it actually appears about 14% bigger than when it’s at its smallest!
Why’s this? The Moon orbits in a giant ellipse around our Earth, where sometimes it’s at its closest to us and sometimes it’s at its farthest. And most of the time, this is what’s responsible for how large the Moon appears.
Not only that, but some perigees — the point of the Moon’s closest approach to Earth — are closer to us than others! These slight variations are due to the gravitational forces of other objects (mostly the Sun) in our Solar system, and it causes the actual perigee and apogee (when the Moon is farthest from Earth) distances to vary, periodically, over time!
In addition to that, the Moon is exactly 100% full only one instant a month, and that moment is very unlikely to line up with the exact moment of perigee. In other words, sometimes we see the Moon full near perigee, sometimes near apogee, and most of the time somewhere in-between.
Well, the last near-perfect alignment between the full Moon and perigee happened in 1992, and the next one happens on Saturday! And that’s what the Supermoon is!
Of course, it won’t look like this! The Moon will, in actuality, still be some 350,000 kilometers away from us, and instead of taking up the meager “half-a-degree”, will take up about 0.56 degrees on the sky!
And, as you may have heard, some people are attributing natural disasters galore to the “Supermoon.”
So what are the real facts? Well, we told you earlier this week what causes Earthquakes, and it isn’t the tides. But the “Supermoon” will cause the highest high tides and the lowest low tides we’ve seen in a long time, but only by about an inch.
The Moon is so gravitationally weak and distant, compared to the Earth, that it simply can’t affect us nearly as much as our internal processes do; and that’s what really causes things like earthquakes, volcanoes, etc.
But it could work the other way around! Back during the Apollo Moon Landing Missions, we installed seismometers on the Moon, and know what we found? We get Moonquakes all the time!
Above was the first one, installed by Buzz Aldrin, who’s pictured above. The causes of all the Moonquakes — particularly the deep ones — are still unknown, and the Earth’s tidal forces on the Moon are one possibility! But the Moon won’t be doing anything more than looking huge and beautiful in the night sky, where it will be the biggest and brightest it’s been in 18 years on Saturday!