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The night sky for September 2014

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during September 2014.

The Summer Triangle consisting of the stars Vega, Deneb and Altair is still high in the sky. The asterism of the Northern Cross, near to Deneb, contains the multicoloured double star Albireo. Another double star, Epsilon Lyrae, can be found using binoculars near to Vega, and a telescope reveals that it is itself a pair of doubles. The constellation of Delphinus is below the Summer Triangle, with Aquarius and Capricornus further down still. The Square of Pegasus rises in the east as the evening progresses, and following the arc of the head of Pegasus leads to the globular cluster M15, while the top-left corner of the Square (or, alternatively, the topmost stars of Cassiopeia) can be used to locate the Andromeda Galaxy. Perseus is in the north-east, below Cassiopeia, and binoculars show that the Double Cluster, a pair of open star clusters, lies between them.

The Planets


Southern Hemisphere

Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during September 2014.

The spring equinox arrives this month, so the nights are rapidly getting shorter. The bright stars Vega and Canopus mark the northern and southern horizons at dusk, with the band of the Milky Way passing overhead between them. Vega is part of the Winter Triangle, along with Deneb and Altair. Between Vega and Altair is the lovely double star Albireo, marking the beak of Cygnus the Swan. The winter constellations of Scorpius and Sagittarius are sliding towards the western horizon night by night, with Orion rising opposite them as they set. Between them are Capricornus, Aquarius and Pisces.

Capricornus, often depicted as a cross between a goat and a fish, appears as an elongated triangle of stars, while a smaller triangle marks its head and horns. Its brightest star is Delta Capricorni or Deneb Algedi, and it changes significantly in brightness because it is an eclipsing binary, in which two stars partially block one another from our view as they orbit. The system is now known to contain four stars. Alpha Capricorni, or Algedi, is a double star whose members can just be distinguished with the naked eye, but the two stars are not in a binary system as they are at very different distances from us. The watery constellations in this part of the sky are associated with autumn and winter rains in the northern hemisphere, and to the south-east of Capricornus is Piscis Austrinus, the Southern Fish. The bright star Fomalhaut, marking its mouth, has a planetary companion that was directly imaged by the Hubble Space Telescope.

The constellation of Aquarius the Water-carrier, lying between Fomalhaut and Altair, contains a number of beautiful deep-sky objects. M2 is a globular cluster near to the third-magnitude star Beta Aquarii. Visible in binoculars, a telescope of 20 centimetres in aperture shows up individual stars. The Helix Nebula, or NGC 7293, is a planetary nebula positioned south-west of Delta Aquarii that appears as a hazy circle in binoculars. A telescope reveals the darker area in the centre, while a long-exposure photograph brings out the nebula's colours. Pisces, Cetus and Delphinus are more water-themed constellations in this area of the sky.

The Planets


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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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