On February 16th, Mercury the innermost planet reaches greatest eastern elongation (18 degrees) and is therefore visible as an early evening object during the first part of the month. As always, opportunities to view Mercury are limited by it closeness to the Sun; the planet never ventures more than 28 degrees from our star, is easily visible on only a few occasions per year, almost always in twilight and never against a black midnight sky.

Due to the angle of the ecliptic, an apparition of Mercury is often better seen from a particular hemisphere. For this apparition, Mercury is best seen from the northern hemisphere. This also happens to be the most favourable evening apparition of the year for northern hemisphere observers. The planet is also visible this month from tropical latitudes, but unfortunately from the southern hemisphere, Mercury is inconveniently placed and not readily observable.

Observing Mercury

A clear unobstructed view of the west-southwestern horizon is essential when searching for Mercury. At the time of greatest elongation east, Mercury is positioned only 18 degrees from the Sun. This means after sunset and when the sky is dark enough to spot the planet, it will be only a few degrees above the horizon at best. For example, the diagram below shows the altitude of Mercury 45 minutes after sunset when viewed from latitude of 51.5N (e.g. London, England). A similar view exists at other northern temperate latitudes.

Mercury Northern Hemisphere view - February 2013 - pdf format

Of course, Mercury reaches it's highest point in the sky on February 16th, the date of greatest elongation east. With an altitude of 9 degrees and shining at magnitude -0.7, the planet should be an easy naked eye target towards the west-southwestern horizon, 45 minutes after sunset. Mercury should also be visible from about February 6th until just after February 20th, although the planet will be lower in the sky. A good idea is to try and spot Mercury early in the month and then observe it on subsequent evenings, watching it rise up to peak altitude before heading back down again.

However, there is a twist in the tail. Ideally we would like Mercury to be at its brightest when highest in the sky. Unfortunately, this is not the case. Mercury starts February at magnitude -1.1 and then decreases in brightness as the month progresses. By February 16th, it shines at magnitude -0.7 and by the 21st its down to magnitude 0.2. As Mercury then draws in towards the Sun the planets brightest decreases dramatically and by months end it shines at only magnitude 3.1.

It is best to start looking for Mercury about 20 to 30 minutes after sunset. Allow your eyes time to relax in the evening twilight and then you should be able to pick out Mercury hovering gently above the horizon.

Mars conjunction

An interesting event occurs on February 8th when Mercury passes 0.3 degrees north of Mars. The "Red planet" is now edging nearer to its April conjunction with the Sun and although visible during the early part of the month, Mars is faint (magnitude 1.2) and an extremely difficult object to spot, especially with the naked eye. However, Mercury at magnitude -1.0 is much brighter than Mars. The best time to start looking for the two planets is about 30 minutes after sunset towards the horizon. As the sky darkens, the bright Mercury should be relatively easy to find and acts as the perfect marker to spot Mars. A pair of binoculars will significantly aid the search, but as always take extreme care when using binoculars at this time of day. The best advice is to start scanning when the Sun is well below the horizon so that you don't accidentally look at it and risk permanent eye damage.

The diagram below illustrates the event with 21 UT the hour of closest approach.

Summary

February offers the best opportunity for northern hemisphere observers this year to catch a glimpse of illusive planet Mercury. The planet will be visible just after sunset, low down towards the west-southwest for a couple of weeks from about February 6th. An added bonus is that Mercury will past within 0.5 degrees of Mars on February 8th, offering an excellent chance to spot both planets.

From the southern hemisphere, Mercury is not suitably placed for observation this month.

Mercury Data Table February 2013