Astroblog: A not so Super "Super Moon"

Saturday, November 12, 2016

A not so Super "Super Moon"

By now everyone has seen the stories that the Full Moon of Monday November 14 is a "Super Moon".

Not just that, a "Super Moon" the likes of which we have not seen since 1948, and will not see again until 2034.

Well, yeah, sort of. Technically, the Moon will be at perigee, when it is closest to the Earth. This is the closest perigee since 1948 (and the next closest will be in 2034).

A full Moon at perigee has been called a "Super Moon", this is not an astronomical term (the astronomical term is perigee syzygy, but that doesn't trip off the tongue so nicely), but an astrological one first coined in 1979 (see here).

However,astronomical outreach groups started using the term "Super Moon" for perigee Moons and it stuck.

Chart comparing the binocular/telescopic appearance of Novembers Full Perigee Moon with the apogee Moon of April 21. Click to embiggen.

What can you expect to see with the "Super Moon" of November 14?

Not much really, unless you are a regular observer of the Moon, have good visual acuity and a good memory.

The problem is, while the Moon is close this time round, it doesn't actually translate into something you can easily see with your unaided eye. Mondays Full Moon will be around 14% larger and 30% brighter than Aprils apogee Full Moon.

So how's you memory?

If you can remember back that far, and remember seeing the Full Moon in April, you now come up against the limits of human eyesight.

The limit of distances that someone with good vision can distinguish between is 1 minute of arc (about the width of a human hair). So, for the vast majority of people any difference smaller than 1 minute of arc cannot be seen. The difference between the Apogee full Moon of 21 April (29'56") and this Mondays perigee "Super" full Moon (33'55") is around 3 minutes of arc, that is 3 human hair widths, doable for most people, but you do have to remember what the Moon looked like back in April, 8 months ago.

Some of my astronomical friends who are regular Moon viewers can do this. On the other hand I have been trying to image perigee and apogee Moons for a couple of years, and I can never tell the difference.

In contrast, the October 16th Full Moon, which you probably can remember, was 33'45'' wide (compared to this months "Super Moon" of 33'55") so the difference is less than one minute of arc, the Full Moon of 17 September was 33'11" wide, again less than one minute of arc, the Full Moon of 14 December will be 33'40" wide so you will not be able to tell the difference between these full Moons and this Monday's "Super Moon".

Recent perigee Full Moons compared to the 2034 and 1948 perigee full Moons, note that there is only a handful of kilometres between them. (source)

Date   Time      Distance    Moon Phase      Year
Nov  25 22:08 356447 km  ++  F-    0h 2034
Jan  26 11:17 356462 km  ++  F+    4h  1948
Nov 14 11:24 356511 km ++ F- 2h 2016
Mar 8 8:36 356529 km ++ F- 1h 1993
Jan 19 22:13 356548 km ++ F+ 0h 1992
Dec 12 21:38 356567 km ++ F+ 4h 2008
Mar 19 19:10 356577 km ++ F+ 0h 2011
Jan 30 9:04 356592 km ++ F+ 2h 2010
Nov 4 0:42 356614 km ++ F- 4h 1998
Dec 22 11:01 356654 km ++ F- 6h 2001
Dec 22 11:01 356654 km ++ F- 6h 1999
Oct 26 11:52 356754 km ++ F+ 6h 2007
Feb 7 22:20 356852 km ++ F- 8h 2002
Sep 28 1:47 356876 km ++ F- 1h 2015
Aug 10 17:44 356896 km ++ F- 0h 2014
Apr 25 17:18 356925 km ++ F- 2h 1994
Jul 30 7:37 356948 km ++ F- 2h 1996
May 6 3:34 356953 km ++ F- 0h 2012
Sep 16 15:25 356965 km + F- 3h 1997
Jun 23 11:11 356989 km ++ F- 0h 2013
Jun 13 1:06 357006 km + F- 2h 1995
Apr 17 4:59 357157 km + F+ 9h 2003
Jul 21 19:46 357159 km  F+ 8h 2005
Sep 8 3:08 357174 km + F+ 8h 2006
Jun 3 13:11 357248 km ++ F+ 8h 2004
Jan 10 10:53 357500 km + F- 16h 2009
Dec 22 9:29 358353 km  F+ 23h 1991
Nov 14 22:59 366050 km  F+3d 1h 2000

Another twist is that the time of perigee is 11:24 UT, which is 22:24 AEDST, so reasonably later at night. The reason why I emphasis this is that many people will see the Moon rising on the horizon, where it will look bigger due to the Moon illusion and say "I've seen the super Moon" , when no, they haven't, the Moon won't be "super sized" until two hours after it rises.

While all but a few dedicated Moon watchers will be able to see the difference between this "Super Moon" and an apogee Moon, photographing it is another thing entirely. Here are some images of the "Super Moon" of August 2014 that I took. Again, it helps to have images of an apogee Moon to compare with, but you are going to have to wait until 8 June 2017 for your next apogee Moon opportunity.

However, as the Moon is rising it is also increasing in size, so a series of images could capture the size increase towards perigee. However, you WILL need a good zoom lens, binoculars or telescope to capture this, the magnification of an ordinary camera will be insufficient to pick up the size difference.

So, the once in 70 years "Super Moon" will be a little bit disappointing if you are not an obsessive Moon watcher with a good memory, but it will still be a beautiful Full Moon, and if you are handy with a camera and telescope you can capture the Moon as it increases in size, and if you capture next years apogee Moon you can make some nice contrasting images.

Labels: astrophotography, Moon, public outreach

# posted by Ian Musgrave @ 1:20 am

Comments:

Supermoon is "super" if we use telephoto lenses. But if we're about to see it with naked eyes, then it's not totally remarkable. At least in papers it would look as if people with zoom lenses get a glimpse of it.

# posted by