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On March 31st, the inner planet Mercury reaches greatest western elongation and on this date is positioned 28 degrees from the Sun in the morning sky. This is an excellent opportunity for observers located at southern hemisphere and tropical latitudes; the planet is visible for an extended period of up to 6 weeks from about the middle of March. Unfortunately for those located further north, the angle of the ecliptic is unfavourable and consequently the planet is not suitably placed for observation.

MESSENGER spacecraft image of Mercury's southern hemisphere (NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

Observing Mercury

A clear and ideally unobstructed view of the eastern horizon is recommended when searching for Mercury. On March 16th, from latitude 35S (approx. equal to Sydney, Cape Town and Santiago) Mercury will appear 11 degrees above the eastern horizon 30 minutes before sunrise. Although placed in the morning twilight, at magnitude 1.4 the planet should be a relatively easy naked eye target.

For this apparition, a good time period to look for Mercury is between March 21st and April 15th, when the planet will be at least 17 degrees above the eastern horizon, 30 minutes before sunrise. Its magnitude will also increase from 0.7 to -0.1 and therefore spotting Mercury should be very easy now, weather permitting of course! The peak altitude occurs on March 31st, the date of greatest elongation west, when Mercury is just over 20 degrees high with a magnitude of 0.2.

Once past greatest elongation west, Mercury continues to brighten as it begins to draw towards the Sun. For this apparition, the planet does not reach maximum brightness (mag -1.0) until the very end of the visibility period, more than 4 weeks after greatest elongation west!

The diagram below shows the March and April morning apparition of Mercury from latitude of 35S. The view will be similar for observers at latitudes near 35S.

Mercury morning apparition as seen from 35S, 30 minutes before sunrise

Mercury data table from March 15 to April 30, 2013

DateRight AscensionDeclinationMag.SizeIllum. (%)Distance from Earth (AU)
Mar 15, 201322h 27m 55s-07d 39m 51s1.610.1"170.663
Mar 16, 201322h 27m 22s-07d 58m 56s1.410.0"190.674
Mar 17, 201322h 27m 13s-08d 15m 40s1.209.8"220.685
Mar 18, 201322h 27m 27s-08d 30m 03s1.109.7"240.696
Mar 19, 201322h 28m 03s-08d 42m 02s0.909.5"260.709
Mar 20, 201322h 29m 00s-08d 51m 39s0.809.3"280.721
Mar 21, 201322h 30m 18s-08d 58m 55s0.709.2"310.734
Mar 22, 201322h 31m 54s-09d 03m 53s0.609.0"330.748
Mar 23, 201322h 33m 48s-09d 06m 35s0.608.8"350.762
Mar 24, 201322h 35m 59s-09d 07m 06s0.508.7"370.776
Mar 25, 201322h 38m 26s-09d 05m 29s0.408.5"390.790
Mar 26, 201322h 41m 07s-09d 01m 48s0.408.4"410.804
Mar 27, 201322h 44m 02s-08d 56m 06s0.408.2"430.818
Mar 28, 201322h 47m 09s-08d 48m 27s0.308.1"440.833
Mar 29, 201322h 50m 29s-08d 38m 55s0.307.9"460.847
Mar 30, 201322h 53m 59s-08d 27m 33s0.307.8"480.862
Mar 31, 201322h 57m 41s-08d 14m 25s0.207.7"490.877
Apr 01, 201323h 01m 31s-07d 59m 33s0.207.5"510.891
Apr 02, 201323h 05m 31s-07d 43m 01s0.207.4"520.906
Apr 03, 201323h 09m 40s-07d 24m 52s0.207.3"540.920
Apr 04, 201323h 13m 57s-07d 05m 09s0.107.2"550.935
Apr 05, 201323h 18m 21s-06d 43m 54s0.107.1"570.950
Apr 06, 201323h 22m 52s-06d 21m 10s0.107.0"580.964
Apr 07, 201323h 27m 31s-05d 56m 60s0.106.9"590.978
Apr 08, 201323h 32m 16s-05d 31m 25s0.106.8"610.993
Apr 09, 201323h 37m 07s-05d 04m 28s0.006.7"621.007
Apr 10, 201323h 42m 05s-04d 36m 11s0.006.6"631.021
Apr 11, 201323h 47m 08s-04d 06m 37s0.006.5"651.035
Apr 12, 201323h 52m 17s-03d 35m 47s0.006.4"661.049
Apr 13, 201323h 57m 32s-03d 03m 43s-0.106.3"671.063
Apr 14, 201300h 02m 52s-02d 30m 28s-0.106.2"681.077
Apr 15, 201300h 08m 17s-01d 56m 02s-0.106.2"701.091
Apr 16, 201300h 13m 48s-01d 20m 28s-0.206.1"711.104
Apr 17, 201300h 19m 25s00d 43m 48s-0.206.0"721.118
Apr 18, 201300h 25m 07s00d 06m 04s-0.205.9"731.131
Apr 19, 201300h 30m 54s00d 32m 44s-0.305.9"751.144
Apr 20, 201300h 36m 47s01d 12m 31s-0.305.8"761.157
Apr 21, 201300h 42m 46s01d 53m 17s-0.305.8"771.170
Apr 22, 201300h 48m 51s02d 35m 00s-0.405.7"791.182
Apr 23, 201300h 55m 01s03d 17m 37s-0.405.6"801.195
Apr 24, 201301h 01m 18s04d 01m 06s-0.505.6"811.207
Apr 25, 201301h 07m 41s04d 45m 25s-0.505.5"831.218
Apr 26, 201301h 14m 11s05d 30m 30s-0.605.5"841.230
Apr 27, 201301h 20m 48s06d 16m 19s-0.705.4"851.241
Apr 28, 201301h 27m 32s07d 02m 48s-0.705.4"871.251
Apr 29, 201301h 34m 23s07d 49m 54s-0.805.3"881.262
Apr 30, 201301h 41m 22s08d 37m 32s-0.905.3"891.271