27 May 2013 -- Evening Sky
By Martin Lewicki, Adelaide Planetarium, South Australia.
On the evening of 27 May skywatchers can spot a close triangle of Mercury, Venus and Jupiter low in the west just after sunset. They will be within a circle diameter 2.4° and 16° elongation from the Sun. Due to the low angle of the ecliptic they will be only a few degrees above the horizon in the west and may be difficult to pick in the bright twilight, so binoculars should help in finding them.
Venus (mag -3.9) is emerging into the twilight as the Evening Star, as it swings around from the far side of the Sun after superior conjunction on 28 March. Mercury (mag -0.7) is also swinging around from the far side of the Sun from its superior conjunction on 11 May and both line up with Jupiter (mag -1.9) on the 27th.
While they all look as though they are near each other, they are merely aligned along a line of sight from Earth's view point and are spread apart by hundreds of millions kilometres, as seen in the accompanying solar system illustration.
In the following days the planets will spread apart. Jupiter will drop to the horizon disappearing from the evening sky by mid-June while Mercury and Venus will climb higher in the western sky. They will stay within 6° of each other until Mercury drops back to the horizon by late June to its inferior conjunction leaving Venus to dominate the evening sky for the remainder of the year.
Martin Lewicki is an Astronomy educator at the Adelaide Planetarium in South Australia. A member of the Astronomical Society of South Australia he heads their light pollution section and especially enjoys following the meanderings of the planets and looking out for those occasional enchanting groupings in the night sky.
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