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Mercury Spotting Guide for 2007
Submitted: Tuesday, 26th September 2006 by Edosaurus Rex

Mercury Spotting:

Altitude at Civil Twilight versus Day of the Year of Greatest Elongation

In hunting for the elusive planet Mercury you have the best chance to catch it near its Greatest Elongations. You will notice however that there are some times of the year when it is easy and others when it is difficult to find.  Whether you are looking for a “morning” or an “evening” Mercury will matter as well. 

With an orbital eccentricity hovering around 0.2 the resulting maximum elongation is about 27 degrees when Mercury is near aphelion and a minimum of 18 degrees when near perihelion.  One would think the near aphelic elongation is the easiest to see but position along the Ecliptic and latitude are also very key players.

Below are two graphs that show the elongation and altitude at Civil Twilight of Mercury when greatest elongation happens on the given day of the year. The Civil Twilight altitude is based on a latitude of S30 degrees and takes atmospheric refraction into account.  For example, we just had a Greatest Western Elongation (morning appearance) on Aug 8th.  From the graph below you can see that the elongation was about 19 degrees and the altitude at Civil Twilight around 7 degrees – normally a challenge this one was made easier by Mercury’s proximity to bright Venus.

Mercury Elongations for 2007

EASTERN         07 FEB      18.2 DEG
WESTERN         22 MAR      27.7 DEG
EASTERN         02 JUN      23.4 DEG
WESTERN         20 JUL      20.3 DEG
EASTERN         29 SEP      26.0 DEG
WESTERN         08 NOV      19.0 DEG

Get your young children involved in helping you search.  Figure out ahead of time if Mercury will be near another planet or bright star, if not you’ll have to “wing it”.  Once you find it move around so a nearby tree, chimney, light pole, or other object is below Mercury.  Have your child stand in front of you and say, “Just look above the tree/chimney/light pole/etc”  Nothing is neater when you hear them say (with enthusiasm), “I see it!” or “There it is!”.


Click to Enlarge
Eastern Elongation (Evening)

Click to Enlarge
Western Elongation (Morning)
Article by Ed (edosaurus_rex). Discuss this article on the IceInSpace Forum.
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