Supermoon (or not)

Super Moon
Monday, November 14, 2016 


Several people on campus have been asking us astronomers what the deal is with the "supermoon" on Sunday, November 13, and tonight, November 14. A supermoon happens whenever the full Moon coincides with the Moon's closest approach to Earth (perigee) in it's slightly elliptical orbit. Because of the way the orbits work, this one will be the closest approach during a full Moon since 1948. Here is some information from NASA and space.com.

The "supermoon" over D.C. Photo by Flickr User Stan Mouser

Now, astronomers are actually fighting as to wether or not the supermoon is noticeable to the naked eye, with some going to the extreme saying that it may even be misleading to mention it in the press. This superest of supermoons will appear about 15 percent larger that a regular full Moon. One camp argues that the human eye/brain is notorious for distorting angular sizes based on what is in the eye's field of view, and that a 15 percent difference lies well within the noise of that effect. Indeed, we have all observed the Sun, Moon, and constellations appear much larger when low in the horizon, where the eye has other objects in the field of view. Similarly, they argue that the about 30 percent increase in brightness is too small to be noticed by the eye's logarithmic response. Others will swear that they notice the effect and that it is not a placebo. Who is right and who is wrong? Go out and judge for yourself!

The Moon rose Sunday at 4:43 p.m. and at 5:30 p.m. on Monday. It is rising slightly North of East. Just like the Sun this time of the year, it stays low on the horizon for a few hours after rising, which, if you have a clear view, will give you a good opportunity to see it when your brain tricks you into thinking that it is actually much larger than when it is high in the sky. My guess is that, unfortunately, the trees and hills at Carnegie's Broad Branch Road campus will prevent us from seeing it from there until a few hours after dark.

Written by Sergio Dieterich
November 14, 2016

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