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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.

Mercury as seen by the Messenger space probe (NASA)

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

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.

Mercury and Mars - February 2013


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

DateRight AscensionDeclinationMagnitudeApparent SizeIllumination (%)Distance from Earth(AU)Constellation
February 121h 38m 45.1s-15d 53m 17.9s-1.15.2"951.301Capricornus
February 221h 45m 31.8s-15d 13m 38.3s-1.15.2"931.286Capricornus
February 321h 52m 14.3s-14d 32m 45.0s-1.15.3"921.269Capricornus
February 421h 58m 52.0s-13d 50m 43.3s-1.15.4"911.252Aquarius
February 522h 05m 24.1s-13d 07m 39.4s-1.15.5"891.234Aquarius
February 622h 11m 49.6s-12d 23m 40.9s-1.15.5"871.214Aquarius
February 722h 18m 07.4s-11d 38m 56.5s-1.15.6"851.194Aquarius
February 822h 24m 16.3s-10d 53m 36.6s-1.05.7"831.172Aquarius
February 922h 30m 15.0s-10d 07m 53.1s-1.05.9"801.149Aquarius
February 1022h 36m 01.8s-09d 21m 59.7s-1.06.0"771.126Aquarius
February 1122h 41m 35.0s-08d 36m 12.0s-1.06.1"741.101Aquarius
February 1222h 46m 52.7s-07d 50m 47.2s-0.96.3"711.076Aquarius
February 1322h 51m 53.0s-07d 06m 04.4s-0.96.4"671.049Aquarius
February 1422h 56m 33.6s-06d 22m 24.5s-0.86.6"631.022Aquarius
February 1523h 00m 52.3s-05d 40m 09.8s-0.86.8"590.994Aquarius
February 1623h 04m 46.7s-04d 59m 43.8s-0.77.0"540.966Aquarius
February 1723h 08m 14.6s-04d 21m 30.8s-0.67.2"500.938Aquarius
February 1823h 11m 13.8s-03d 45m 55.7s-0.47.4"450.910Aquarius
February 1923h 13m 42.3s-03d 13m 23.1s-0.37.6"400.882Pisces
February 2023h 15m 38.1s-02d 44m 17.1s-0.17.9"360.855Pisces
February 2123h 16m 59.9s-02d 19m 00.2s0.28.1"310.828Pisces
February 2223h 17m 46.5s-01d 57m 53.1s0.58.4"270.802Pisces
February 2323h 17m 57.6s-01d 41m 13.7s0.88.7"220.777Pisces
February 2423h 17m 33.0s-01d 29m 16.2s1.18.9"180.754Pisces
February 2523h 16m 33.7s-01d 22m 10.5s1.69.2"150.732Pisces
February 2623h 15m 01.2s-01d 20m 01.4s2.09.4"110.712Pisces
February 2723h 12m 57.8s-01d 22m 47.7s2.59.7"080.694Pisces
February 2823h 10m 26.5s-01d 30m 21.7s3.19.9"060.677Pisces