Mercury, the innermost planet of the solar system, swings to its greatest evening elongation (26o east of the setting sun) on September 21, 2014. Then, a little more than one day later, it’ll be the September equinox. So, in September 2014, Mercury’s greatest evening elongation pretty much comes concurrently with the September equinox. And that means Mercury will not be easy to see from the Northern Hemisphere, but Southern Hemisphere viewers will have a grand view.
Mercury pairs up with the star Spica, the brightest star in the constellation Virgo the Maiden, around this time. Mercury, slightly brighter than Spica, takes stage in the same binocular field of view for several days, centered around September 20.
The most favorable time to see Mercury in the evening sky is when this planet’s greatest eastern (evening) elongation closely coincides with the spring equinox. Because the September equinox is the Southern Hemisphere’s spring equinox, southerly latitudes get to see a wonderful evening apparition of Mercury throughout the month of September.
However, in the Northern Hemisphere, the September equinox is the autumn equinox. Unfortunately, Mercury’s presence in the evening sky is most subdued when its greatest evening elongation happens in close conjunction with the autumn equinox. That’s why the Southern Hemisphere has it better than the Northern Hemisphere for this particular evening apparition of Mercury.
At southern temperate latitudes, Mercury sets about 2.5 hours after the sun, while at mid-northern latitudes Mercury follows the sun beneath the horizon less than one hour after sundown.
There is a consolation prize, however! Even at mid-northern latitudes, we should be able to catch the planets Mars and Saturn, plus the star Antares, in the southwest sky at nightfall. See the chart below.
Bottom line: As seen from around the world, Mercury, the innermost planet of the solar system, reaches its greatest evening elongation of 26o east of the setting sun on September 21, 2014. Thus Mercury is at its best for this evening apparition around September 21. It’s an awesome apparition for the Southern Hemisphere, and a poor one for the Northern Hemisphere. If you get pics, post them at EarthSky Facebook, or submit photos here.