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Mercury reaches greatest western elongation on May 17th, when it will be positioned 25.8 degrees from the Sun. This apparition offers an excellent opportunity for observers at southern and tropical latitudes to spot the elusive planet. From such locations, Mercury can be seen low down above the east-northeastern horizon just before sunrise throughout May and until the second week of June. However, from northern temperate locations the planet is not well placed, although from some locations it can be spotted around the time of greatest elongation but always very close to the horizon.

Mercury as imaged by the MESSENGER spacecraft (credit - NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

On May 1st, from latitude 35S (approx. equal to Sydney, Cape Town and Santiago), Mercury was a difficult object due to its brightness at magnitude +2.5 and position close to the horizon. As the month progressed the visibility of Mercury improved and will continue to do so until greatest elongation is reached. On that day, the planet will shine at magnitude +0.5 and be 15 degrees above the east-northeastern horizon, 45 minutes before sunrise. For the remainder of the month it gradually sinks back towards the horizon. It should be noted that Mercury improves in brightness throughout May and on the 31st it will shine at magnitude -0.3. Brilliant Venus is positioned above Mercury throughout this time.

The thin waning crescent Moon passes 2 degrees south of Mercury on May 24th.

Mercury, 45 minutes before sunrise, from mid-latitude southern locations (credit:- freestarcharts)

Mercury and Venus as seen from mid-southern latitudes, 45 minutes before sunrise, on May 17, 2017 (credit:- stellarium/freestarcharts)