See Mercury at its best, Venus and a young Moon in the March evening sky

By Ade Ashford

12 March 2018 Ade Ashford

Mercury attains a greatest easterly elongation of 18 degrees from the Sun on 15 March, the innermost planet’s best evening showing for Northern Hemisphere observers for the entire year. This looping animation simulates the horizon view due west in bright twilight 45 minutes after sunset from 12–20 March as seen from the heart of the British Isles. Note the changing configuration of planets Mercury and Venus over the next eight days, but they remain almost 4 degrees apart and hence visible in the same field of view of typical 7× to 10× magnification binoculars. The Moon’s size has been enlarged for clarity. AN animation by Ade Ashford.
Mercury passed through superior conjunction on 17 February making it an evening object, but northern observers have had to wait for the innermost planet to move far enough from the solar glare to be glimpsed low in the west in bright twilight. Mercury attains a greatest easterly elongation of 18 degrees from the Sun on 15 March, so the coming week offers the planet’s best evening showing for the entire year for Northern Hemisphere observers.

For observers in the British Isles, the best time to look for Mercury from 12 –20 March is about 45 minutes after sunset (hint: you can use our interactive online Almanac to calculate sunset times for your location) when the planet remains high enough above the horizon to be seen yet twilight is not too bright. To ensure success, you will need to find a location that offers a level horizon due west unobstructed by houses or trees.

The task of spotting Mercury is currently made somewhat easier due to its close proximity to sibling planet Venus. From 12 –20 March, the two planets change configuration with respect to the horizon, but their angular separation hovers close to 4 degrees. This means that over the next eight days, once you locate bright magnitude -3.9 Venus, Mercury lies in the same field of view of typical 7× to 10× magnification binoculars.

Mercury is brightest and hence easier to spot over the next few nights. Shining at magnitude -0.6 on Monday, 12 March, the planet fades to magnitude zero by 16 March. By the time the slender crescent of a young Moon arrives on the scene on 18 March, Mercury will be magnitude +0.4.

If the sky remains clear 45 minutes after sunset on Monday, 19 March, don’t miss an attractive conjunction of the 2¼-day-old crescent Moon, Venus and Mercury all encompassed by little more than half the span of an outstretched hand at arm’s length.

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