July 23, 2017

Mercury-Spotting during the First Elongation of 2013.

Mercury as seen by Messenger during its

3rd flyby in 2009.

(Credit: NASA/JPL).

I SEE IT! Catching a glimpse of fleeting Mercury can be an unforgettable experience; orbiting the Sun once every 88 days, the innermost planet never strays far from its perch low in the dawn or dusk sky. February offers your first shot at catching the world low in the dusk as it approaches its first of six elongations in 2013. Though not the best of 2013 for most viewers worldwide (see below), this month’s elongation does offer roughly equal prospects for both northern and southern hemisphere observers as the ecliptic approaches near-perpendicular to the horizon headed towards the March equinox. And as you’ll see, this apparition will set us up for some of the best prospects for catching Mercury later this spring.

Looking west post-sunset… the apparent path of Mercury through February.

(Graphics created by the author in Starry Night).

And speaking of which, one caveat is in order; several sites have already been touting the February dusk elongation as “the best for 2013,” but this only holds true for perhaps those located above latitudes 45° degrees north. The further south you go, the less this is so. It’s a funny thing with the modern day web; like meteor showers and perigee Full Moons, each Mercury apparition is now hyped as “the best!!!” But as astute watchers of the planets know, not all appearances of the innermost planet are created equal!

Mercury versus Mars during closest approach on February 8th.

But there is one sure “Best of 2013″ in the offing. Be sure not to miss the closest conjunctions of two naked eye planets in 2013 involving Mercury and Mars on the evening of February 8th. Mars has been “hanging out” in the dusk sky for several months enroute to its conjunction with the Sun and subsequent transition into the dawn sky on April 18th, 2013. Mercury will pass less than 15’ arc minutes from Mars on February 8th at 17:00UT/12:00EST. For contrast, Mercury will shine at magnitude -1.0 and be 77% illuminated with a 6” disc, while Mars will be 7 times fainter at magnitude +1.2 with a 4” disc. Can you spy both with the naked eye? Binoculars will be a definite help with this one. This pairing will be visible worldwide with closest approach favoring areas around Eastern Europe & the Middle East at dusk.

An even tougher challenge, Mercury also passes +8th magnitude Neptune on February 6th around 23:00UT with less than 25’ arc minutes of separation. Both of these pairings would be a fun time to try and catch an image of Mercury with a “faux moon” around either date. Fun fact: did you know that for a very brief time, researchers thought they’d discovered a moon around Mercury during the flyby of Mariner 10? Messenger has even been on the lookout for any Mercurial satellites as well as Vulcanoids during its exploration of the planet. Another spurious “Mercurial Moon” dubbed Caduceus was added to astronomy lore during an April Fool’s Day prank in 2012!

But back to reality. Adding to the action, the 33-hour old Moon then passes within 5° degrees of Mercury on February 11th. This will provide a great guidepost to the planetary action; just how soon after New can you spy the Moon? This is always a great feat of “visual athletics” to try. First sightings of the uber-thin crescent Moon below Mercury favors northeastern North America on the evening of February 10th.

Looking west 30 minutes after sunset on February 10th from latitude 30 north.

The evening February 17th sees the best chance of spying Mercury, with a greatest eastern elongation of 18.1° degrees from the Sun occurring at 21:00 UT/4:00 PM EST just 5 hours prior to perihelion. Thus, this is very nearly the shortest elongation that can occur, which is 17.9° degrees; the last time we had a “perihelion-elongation” was on September 3rd, 2011 & the next won’t occur until October 16th 2015.

And of course, this sets us up for an exceptionally loooong aphelion-elongation of 27.8° degrees in the dawn sky at the end of March… more to come on that this spring! Good luck, and happy “Mercury-Hunting”!



  1. [...] Mercury passes 0.3° degrees north of Mars. Both are about 15° degrees east of the Sun at dusk. This is the closest naked eye [...]

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