Supermoon

The media has made a big deal this week about the “Supermoon.” CNN did a story and posted number of images. I have seen stories on the evening new on all of the networks.

I find the entire story a bit overblown.

The usual hype is that the moon is 11% or 14% bigger and 30% brighter. What the stories don’t say is what they are comparing to. As it turns out the ratios are the smallest the moon gets to the largest it gets as seen from the Earth. The 11% figure is based on averages while the 14% figure is based on the extremes over several centuries. The size of the full moon varies over a cycle with a length of about a year as the full moon occurs at various points in the moon’s orbit about the Earth.

Wikipedia does a fine job of explaining the orbital dynamics involved. But better than that a German site provides some of the relevant numbers to do a few useful calculation. I did a few of them and they gave me the results I expected.

On June 23, 2013 at the time of the full moon it was 356,991 kilometers from the Earth. On January 16, 2014 it will be 406,528 from the Earth. So this month is was almost 14% bigger than it will be next January when it will be at its smallest. Does that qualify it as a “Supermoon?”

Not so fast. The next full moon will be on July 22. At that time the moon will be 359,169 kilometers from the Earth. Guess what. It was less than 1% bigger this month and just over 1% brighter than it will be next month at the time of the full moon.

Somehow I don’t get the feeling I missed much by not making any effort to go out and see this media defined rare event.