Aug 102014

Moons for All SizesWhat is a Super Moon?

Coined in 1979 in an astrology magazine, the “Super Moon” is simply the full moon (or new moon) that occurs within 90% or closer of its closest possible approach to the Earth during a given orbit.  It’s also a lot easier to say than its astronomical term, perigee-syzygy Moon.

Today at 2pm Eastren, the full moon will reach perigee just a hair under 220,000 miles from the Earth.  It will appear as much as 14% bigger than usual and correspondingly brighter.  However, astropotamuses in North America won’t see it since it happens in the middle of the day.  In fact, this ‘potamus will be at a baseball game.

Even if it were visible, you probably wouldn’t notice.  That’s because we don’t remember the full moon from one to another with enough clarity to be able to tell.  Photographic evidence would show a difference if you were careful enough to take pictures with the same camera, lens, and settings on a Super Moon night versus a “normal Moon” night.

From 1990 to 2020, the Moon’s closest approach to Earth will occur on November 14, 2016.  It will be 221,524 miles away and be a full moon.  Since astronomers measure astronomical distances from the centers of bodies, that means the surfaces of the Earth and the Moon will be almost 5,000 miles closer than distance between their centers.

The smallest full moon of 2014 was on January 15th with the moon 252,607 miles away.  That means today’s full moon will be over 30,000 miles closer, which is 12.2% closer and therefore 26% brighter.  That’s a mangitude difference of .25 or the difference between Betelgeuse at magnitude 0.58 and Aldebaran at magnitude 0.85.

If you look a these two stars in the same night in North America (and they are visible together) you could generally tell that Betelgeuse is brighter.  But if you looked at Aldebaran in January and then seven months later looked at Betelgeuse in August, would you remember how much brighter the first one was?

I’ll leave you with a picture that I did not take (Anthony Ayoimanitis did) that shows a full moon in 2006 and a full moon in 2005.  The 2006 moon on the left is at apogee (the farthest point away) and the 2005 moon on the right is at perigee (the closest point in its orbit).  Decide for yourself if you would notice a difference if they were hanging in the sky outside your backdoor, a month apart from each other.

Aug 032014

This old Astropotamus is about to dust off the Time Machine again.  It’s been a while.  Please excuse the lateness of my reply, but do start looking for upcoming posts again.