October 20, 2017

AstroEvent: A Mutual Western Elongation.

January 8th, about a half hour before sunrise looking west from Tampa, Florida. (Created by the Author in Starry Night).   

One of the more unique events of 2011 occurs this weekend. The interior planets of Mercury and Venus both reach greatest western elongation within 24 hours of each other in the dawn skies. First, Venus reaches an elongation of 47° from the Sun on Saturday, January 8th at about 16:00UT/11:00 EST. Then, about 23.6 hours later, Mercury reaches the height of its morning apparition 23° west of the Sun. The pair will be easily visible to the southeast starting about an hour before local sunrise. Just how rare is a mutual elongation of these two worlds? Reader Ed Kotapish calculates that the last time this occurred was on November 3rd, 2005 and March 29th, 2004 with a spread of 3.3 hours and 2.9 hours respectively, and will next occur on August 16th, 2012 with a wider spread of 26.3 hours. Now is the time to catch these two innermost worlds at their best!  

The astro-term for this week is Inferior Planet. This simply refers to worlds that are interior in their orbits to our own, in other words Mercury and Venus. Mercury orbits the Sun once every 88 days, while Venus orbits the Sun once every 224.7 days. The term dates back to Ptolemy, and was later modified for use by Copernicus as part of the central tenet of heliocentric theory.  These two worlds are also the only two capable of passing through an inferior conjunction between the Earth and the Sun.  In fact, Venus will perform a transit in front of the Sun during its next inferior conjunction on June 5th-6th, 2012, the last of our lifetimes!

…and just how does this week’s mutual elongation stack up? Below is a list spanning a century’s worth of simultaneous apparitions of the inner worlds, again, thanks to Ed Kotapish for working these out!

MUTUAL ELONGATIONS OF MERCURY AND VENUS
1950 TO 2050
ELONG EAST = EVENING, WEST = MORNING
DATE IS FOR MERCURY’S ELONGATION
DIFF (IN DAYS)+ = VENUS AFTER, – = VENUS BEFORE (14 DAYS IS THE MAX)

ELONG MMM DD YYYY  DIFF
 EAST FEB 06 1961  -8.3
 EAST SEP 10 1962  -7.2
 EAST APR 07 1964   2.7
 EAST NOV 13 1965   2.8

 WEST APR 18 1966 -11.9

 EAST JUN 12 1967   8.5

 WEST NOV 17 1967  -8.3

 EAST JAN 13 1969  13.2

 WEST JUN 23 1969  -5.8
 WEST JAN 19 1971   1.6
 WEST AUG 25 1972   1.5
 WEST MAR 23 1974  11.3
 WEST OCT 25 1975  13.2

 EAST JAN 28 2001 -11.2
 EAST SEP 01 2002  -9.9
 EAST MAR 29 2004   0.1
 EAST NOV 03 2005   0.1
 EAST JUN 02 2007   6.8

 WEST NOV 08 2007 -11.2

 EAST JAN 04 2009  10.4
 WEST JUN 13 2009  -7.6

 EAST AUG 07 2010  13.1

 WEST JAN 09 2011  -1.0
 WEST AUG 16 2012  -1.1
 WEST MAR 14 2014   8.6
 WEST OCT 16 2015  10.1

 EAST AUG 22 2042 -12.5 
 EAST MAR 20 2044  -2.6
 EAST OCT 25 2045  -2.5
 EAST MAY 23 2047   5.0
 EAST DEC 26 2048   7.5

 WEST JUN 03 2049  -9.5

 EAST JUL 28 2050  10.6

 WEST DEC 31 2050  -3.5

 

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