A short post about something that is all over the news now. No, not the election. I’m talking about the latest “supermoon”. This is a term I don’t believe I had ever heard before about five years ago. I don’t know who to blame for it, but it refers to a full moon that is—what?—bigger than average? I don’t know who decides what qualifies. OK, enough complaining and eye rolling. Anything that gets people looking at and thinking about the moon is a good thing!
So why would one full moon be bigger than another? The only way would be if the moon were closer to the Earth sometimes than it is at others, right? Correct! You win!
And that is the case because the moon’s orbit around the Earth is not a circle, but an ellipse. The point in the lunar orbit when it is closest to the Earth is called perigee; the most distant point in the orbit is apogee. The diagram below is exaggerated to illustrate the point.
And here is an image showing the extremes of the moon’s apparent size at these two points in its orbit.
What’s so special about the upcoming full moon? The time at which it will be full is only two and a half hours after the time it reaches perigee. It will not be full when it is this close again until 2034. The exact moment for this November’s full moon phase is 8:52 am on November 14th, but either Sunday night the 13th or Monday night the 14th should be equally special.
Enjoy! And if you hear any howling, watch from inside.