Super Moon – Super Bad Science

Graphic Credit: Heart Touching Fun

Graphic Credit: Heart Touching Fun

   File this under the ‘here we go again’ category on Facebook and other social media where this piece of misleading science is floating around.
   According to graphics like this one from Facebook and presumably re-posted and shared on other social media websites the full Moon of 23 June would be the biggest one this year as well as the closest one for the year – a “Super Moon”. So while the part about closest and largest is correct, using the term “Super Moon” is misleading in the sense that there is nothing for comparison and so there will be folks going outside expecting to see a really large appearing full Moon. But how large? As large as the graphic suggests!!
   So what is a “Super Moon”; how “super” is this next full Moon; and in comparison to other full Moons, how significant, if at all, is this ‘event’?
   A “Super Moon” is a full Moon that occurs very near to its time of perigee, the closest the Moon comes to the Earth for that particular orbit, or month. By definition, “very close” would be when the Moon is less than 10% of its orbital period (about 2.9 days to 3.2 days) from the time of perigee. Use the data in the table below to compare the full and new Moon dates, with the apogee (farthest) and perigee dates and distances. Dates for apogee and perigee are given showing how many days and or hours before or after the date of the new or full moon these two distances occur. The June 23rd perigee date is the same as the date for full Moon while the others are offset.
   Here is an idea – use the apogee dates to determine when we will have a “Super Mini-Moon”!
The 2013 Full Moon

The 2013 Full Moons

   By comparing the 23 June distance with other dates and distances, you will see that there are several “Super Moon”s in 2013. In fact, each year there are from four to six occurrences when the full Moon and perigee are close enough to be considered a “Super Moon” – the full Moon closest to the time for perigee is the “Super Moon” for that year. So a “Super Moon” is not that unique nor worthy of the hype this one will receive since we can have several “Super Moon” ever year.
   Carry this analysis further by comparing dates for full Moon and perigee over a several year period, and you’ll find a pattern in the regularity of “Super Moon” events. How? There are two regular time periods, or cycles, involved in the pattern for “Super Moon”. First, the time period between each full Moon, the synodic month, is approximately 29.53 days; second, the time period between each perigee, the anomalistic month, is approximately 27.55 days. With a two-day difference between these two cycles, there is obviously not a super Moon every month. However, with a ratio of 14 synodic months to 15 perigee periods,the closest of the “Super Moons” to perigee will occur about every 14 months. Because of this ratio relationship between these two cycles, 14 full Moons after the full Moon of June 23, 2013 (356,989 km), there will be the closest full Moon of August 10, 2014 (356,896), which will be followed by the closest full Moon of September 28, 2015 (356,877 km), and so on.

   The above has been adapted from my October 2012 Scope on the Skies column in Science Scope Magazine “Apparent Sizes, or It Was This Big”. Click here to download a copy of that column (PDF).

                    
             Perigee                             Apogee
     (N=New Moon; F=Full Moon '-' = before; '+' = after)
           All times are shown in UT (Universal Time)
Jan 10 10:27 360047 km    N-1d 9h   Jan 22 10:53 405311 km    F-4d17h
Feb  7 12:10 365313 km    N-2d19h   Feb 19  6:31 404473 km    F-6d13h
Mar  5 23:21 369953 km    N-5d20h   Mar 19  3:14 404261 km    N+7d 7h
Mar 31  3:56 367493 km    F+3d18h   Apr 15 22:23 404864 km    N+5d12h
Apr 27 19:49 362267 km    F+1d23h   May 13 13:32 405826 km    N+3d13h
May 26  1:46 358374 km    F+  21h   Jun  9 21:41 406486 km -  N+1d 5h
Jun 23 11:11 356989 km ++ F-   0h   Jul  7  0:37 406491 km -- N-1d 6h
Jul 21 20:28 358401 km    F-  21h   Aug  3  8:54 405833 km    N-3d12h
Aug 19  1:27 362264 km    F-2d 0h   Aug 30 23:47 404882 km    N-5d11h
Sep 15 16:35 367387 km    F-3d18h   Sep 27 18:18 404308 km    N-7d 6h
Oct 10 23:07 369811 km    N+5d22h   Oct 25 14:26 404560 km    F+6d14h
Nov  6  9:29 365361 km    N+2d20h   Nov 22  9:51 405445 km    F+4d18h
Dec  4 10:16 360063 km    N+1d 9h   Dec 19 23:50 406267 km +  F+2d14h

   

  Date/Time of New Moon   Date/Time of Full Moon
   2013 Jan 11 19:45        2013 Jan 27  4:40
   2013 Feb 10  7:23        2013 Feb 25 20:29
   2013 Mar 11 19:54        2013 Mar 27  9:30
   2013 Apr 10  9:39        2013 Apr 25 20:00
   2013 May 10  0:32        2013 May 25  4:27
   2013 Jun  8 15:59        2013 Jun 23 11:34
   2013 Jul  8  7:16        2013 Jul 22 18:17
   2013 Aug  6 21:52        2013 Aug 21  1:45
   2013 Sep  5 11:36        2013 Sep 19 11:13
   2013 Oct  5  0:34        2013 Oct 18 23:38
   2013 Nov  3 12:50        2013 Nov 17 15:17
   2013 Dec  3  0:22        2013 Dec 17  9:29     

Data Table Source: Lunar Perigee and Apogee Calculator. http://www.fourmilab.ch/earthview/pacalc.html

   Click here to go to the Qué tal in the Current Skies web site for more observing information.

One thought on “Super Moon – Super Bad Science

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