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Mercury reaches greatest elongation east (GEE) on April 18th when it's positioned 19.9 degrees from the Sun. The nearest planet to the Sun will be visible during April low down above the west-northwestern horizon shortly after sunset. This months apparition offers the best opportunity (evening) for observers at northern latitudes to spot the elusive planet this year. From equatorial regions Mercury is also visible during April but from mid-southern latitudes unfortunately not.

Mercury as seen by the Messenger space probe (credit - NASA)

Observing Mercury

When searching for Mercury a clear unobstructed view of the west-northwestern horizon is essential. Observers should be able to spot the planet about 45 minutes after sunset against the twilight backdrop. What is surprising when looking for Mercury is how close the planet clings to the horizon. For example from London, England (51.5 degrees N) Mercury will be 6 degrees above the horizon 45 minutes after sunset on April 8th. On this evening the nearby thin nearby waxing crescent Moon will acts as a convenient marker. A good period to look is between April 13th and April 23rd when Mercury will be at it's highest in the sky about 10 degrees above the horizon. After that it's altitude decreases quickly until it's lost to the bright twilight near the end of the month. Observers should note that the planet is at its brightest at the start of the month - it decreases from mag. -1.4 to +2.1 as the visibility period progresses.

Thin crescent Moon and Mercury just after sunset from mid-northern temperate latitudes on April 8, 2016 (credit:- stellarium)

The diagram below shows the altitude of Mercury 45 minutes after sunset when viewed from London, England. The view will be similar from other northern temperate locations.

April evening apparition of Mercury as seen from mid-northern temperate latitudes, 45 minutes after sunset (credit:- freestarcharts)

Mercury Data Table April 2016

DateRight AscensionDeclinationApp. Mag.App. SizeIllumin. (%)Dist. from Earth (AU)Constellation
April 0101h 13m 49.1s07d 48m 19.3s-1.505.3"941.266Pisces
April 0201h 21m 06.6s08d 44m 10.2s-1.505.4"921.250Pisces
April 0301h 28m 21.8s09d 39m 17.3s-1.405.5"901.233Pisces
April 0401h 35m 33.5s10d 33m 26.9s-1.305.5"881.214Pisces
April 0501h 42m 40.6s11d 26m 25.6s-1.305.6"851.194Pisces
April 0601h 49m 41.7s12d 18m 00.0s-1.205.7"831.174Aries
April 0701h 56m 35.7s13d 07m 57.1s-1.105.8"801.152Aries
April 0802h 03m 21.1s13d 56m 04.8s-1.006.0"761.129Aries
April 0902h 09m 56.7s14d 42m 12.0s-1.006.1"731.105Aries
April 1002h 16m 21.0s15d 26m 08.6s-0.906.2"691.081Aries
April 1102h 22m 32.8s16d 07m 46.1s-0.806.4"661.056Aries
April 1202h 28m 31.0s16d 46m 57.0s-0.706.5"621.031Aries
April 1302h 34m 14.2s17d 23m 35.3s-0.606.7"591.006Aries
April 1402h 39m 41.6s17d 57m 36.2s-0.506.9"550.980Aries
April 1502h 44m 52.0s18d 28m 55.9s-0.407.0"510.955Aries
April 1602h 49m 44.5s18d 57m 31.8s-0.307.2"480.929Aries
April 1702h 54m 18.2s19d 23m 21.9s-0.207.4"440.904Aries
April 1802h 58m 32.5s19d 46m 24.9s0.007.6"410.880Aries
April 1903h 02m 26.5s20d 06m 40.1s0.107.9"370.855Aries
April 2003h 05m 59.7s20d 24m 07.1s0.308.1"340.831Aries
April 2103h 09m 11.4s20d 38m 46.0s0.508.3"310.808Aries
April 2203h 12m 01.4s20d 50m 36.7s0.608.6"280.786Aries
April 2303h 14m 29.0s20d 59m 39.8s0.808.8"250.764Aries
April 2403h 16m 34.2s21d 05m 55.6s1.109.0"230.743Aries
April 2503h 18m 16.7s21d 09m 25.1s1.309.3"200.724Aries
April 2603h 19m 36.6s21d 10m 09.2s1.509.5"170.705Aries
April 2703h 20m 34.1s21d 08m 09.5s1.809.8"150.686Aries
April 2803h 21m 09.3s21d 03m 28.0s2.110.0"130.669Aries
April 2903h 21m 23.0s20d 56m 07.6s2.410.3"110.654Aries
April 3003h 21m 15.8s20d 46m 12.0s2.710.5"090.639Aries

See also

The Planets this Month - April 2016