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The night sky for May 2015

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during May 2015.

The winter constellations of Orion, Taurus and Gemini are setting in the west after sunset, with Auriga close behind. Leo is higher in the sky to their left, and further over is the bright star Arcturus in Bootes. Between them, in an otherwise fairly blank part of the sky, the Realm of the Galaxies offers 18 Messier objects to telescopic observers. The Summer Triangle rises in the east later in the evening, consisting of the bright stars Vega in Lyra, Deneb in Cygnus and Altair in Aquila. The constellation of Hercules is between Arcturus and Vega, and its four brightest stars make a trapezium called the Keystone. Two-thirds of the way up the Keystone's right-hand side, binoculars can locate the globular cluster M13. The asterism of the Plough is overhead, its hindmost stars, Merak and Dubhe, pointing towards Polaris in the north. Below Polaris is the W-shaped constellation of Cassiopeia.

The Planets


Southern Hemisphere

Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during May 2015

Three bright planets are visible in the early evening. Venus appears low in the north-west as the Sun sets, outshining everything except the Sun and Moon as its atmosphere reflects almost 70 percent of the sunlight that falls on it. Jupiter appears soon after Venus, just to the left of the head of Leo the Lion in the north. It sets around midnight NZST (New Zealand Standard Time, 12 hours ahead of Universal Time) at the beginning of the month and 22:00 at the end, and is near the Moon in the sky on the 24th. Saturn rises a little later in the east, officially in Libra but close to the Claw of Scorpius and to the left of the star Antares. It is at its brightest and closest to us around the time of opposition on the 23rd, and appears high in the north at midnight. Its rings are inclined favourably for viewing, and the Moon passes within 2 degrees of it on the 6th.

On the same night, the Earth's passage through debris from Comet Halley causes the peak of the Eta Aquariid meteor shower, so named because the meteors appear to radiate from a point (the radiant) near the fourth-magnitude star Eta Aquarii in Aquarius. The radiant rises around 02:00 NZST in New Zealand, and up to a meteor a minute may be spotted streaking across the sky - although the Moon will obscure the fainter ones. The more minor Alpha Scorpiid meteor shower peaks on the 13th, its radiant near to Antares and Saturn. Although visible throughout the night and largely unhindered by the thin crescent Moon, it provides no more than 5 meteors per hour.

To the lower-left of Saturn, in the constellation of Serpens, is the globular cluster M5, also called NGC 5904. At magnitude +5.7, binoculars can be used to view it, while a small telescope picks out some of its hundreds of thousands of stars. It is home to over one hundred variable stars, the brightest of which is called Variable 42 and changes from magnitude +10.6 to +12.1 and back every 26.5 days. M5 is around two-thirds of the way from the red star Antares to the orange star Arcturus in Bootes, which rises in the north-east after dark. Above Arcturus is the bright blue star Spica, in Virgo, which is actually a double.

On the opposite side of the sky, Comet C/2015 G2 (MASTER) is expected to reach a peak brightness of magnitude +5.4 on the 14th, making it easily visible in binoculars. The comet begins May in the constellation of Sculptor, resides in Fornax from the 9th to the 14th, moves through Eridanus, Lepus and Canis Major and ends the month in Monoceros. It is visible above the south-western horizon after dusk on the 14th, setting just after 21:00 NZST.

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The Night Sky This Month is one part of the Jodcast. The full show contains the latest news, interviews with astronomers, answers to listener questions and more.

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