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)


Sky Highlights - June 2017

Saturn
Saturn reaches opposition on June 15

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for June

Northern Hemisphere
Evening
Southwest:- Jupiter (mag. -2.2)
Southeast:- Saturn (mag. 0.0)
Midnight
West:- Jupiter
South:- Saturn
Morning
Southwest:- Saturn
Southeast:- Neptune (mag. +7.9)
East:- Venus (mag. -4.3), Uranus (mag. +5.9)

Southern Hemisphere
Evening
North:- Jupiter
East:- Saturn
Midnight
West:- Jupiter
North:- Saturn
Morning
West:- Saturn
Northeast:- Neptune
East:- Venus, Uranus, Mercury (first half of month (mag. -0.4 to -1.2)

Deep Sky

Small telescopes:-
Messier 13 - M13 - Great Hercules Globular Cluster
Messier 92 - M92 - Globular Cluster
Messier 11 - M11 - The Wild Duck Cluster (Open Cluster)
Messier 7 - M7 - The Ptolemy Cluster (Open Cluster)
Messier 6 - M6 - The Butterfly Cluster (Open Cluster)
Messier 4 - M4 - Globular Cluster
Messier 8 - M8 - Lagoon Nebula (Emission Nebula)
Messier 16 - M16 - Eagle Nebula (Emission Nebula with Open Cluster)
Messier 20 - M20 - Trifid Nebula (Emission and Reflection Nebula)

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