Pensford Field Night Sky, September to October 2010
Look south between the horizon and the zenith early in September around 10 pm and see the big triangle of stars. Altair is the lowest and Vega is the brightest high up on the right. Deneb high up on the left is the least bright of the three but it is the leading star of the four that make up the wing of Cygnus (the swan) flying away from Vega. This big triangle was only just rising in the east in early summer. It will still be prominent at the end of October but will be lower in the west. All the constellations rotate around the Pole Star at the rate of 30 degrees per month, anticlockwise if you are looking north, clockwise if you are looking south. (Of course, the night sky or 'celestial sphere' also rotates around the pole at the same daily rate as the earth, once in 24 hours.)
The Plough or Big Dipper, which was overhead in early summer, is now lower down in the north-west. The two stars furthest from the handle always point to Polaris, the not-very-bright Pole Star. On the other side of Polaris, high up towards the east, are the 5 stars of Cassiopeia in the shape of a stretched out W. Like the Plough, this group is 'circumpolar' (above the horizon throughout the year).
Jupiter, the only planet visible in this period, is bright in the east and will be prominent throughout this period. With binoculars, you may be able to see up to 4 of its many moons, faint and in a straight line close to the planet. The square of Pegasus can be seen in the south-east between Jupiter and Cassiopeia; its side length is about one and a half fists held at arm's length. The 4 stars are a bit out of square and not very bright. At the end of this period they will be past south at 10pm. Go to the star of the square nearest to Cassiopeia; now go from that star towards Cassiopeia about the side length of the square. In that region on a clear night you may be able to see with the naked eye a faint fuzzy object, or see it with binoculars. This is the Andromeda galaxy. It is about the same size as our own galaxy, which of course includes all the stars in our Milky Way, and it is over 2,000 million light-years away. The number of galaxies in the universe is of the same order as the number of stars in our galaxy, that is, thousands of millions. On a clear night we can see about 5,000 stars with the naked eye but never more than a few galaxies. The bright star rising in the east early in September is Capella, another circumpolar star. In the early hours of the morning it will be overhead and the constellation of Orion will be rising.
There are new moons on 8 September and 7 October; look for them in the west an hour or two after sunset, two or more days later, when the thin crescent has become thick enough to be seen. Full moons are on 23 September and 23 October. See them rising in the east shortly before or after sunset on, or the day before or after, these dates. It's easier to see the stars when there is no dazzling moon.
The International Space Station (ISS) will be visible and very bright on the following dates in early September. The sightings start low down in the west and last about 4 minutes. The ISS vanishes in the earth's shadow before reaching the eastern horizon. There is a crew on board.
4th: starts 9.45pm, climbs to 84 degrees above horizon.
5th: starts 8.42pm, climbs to 85 degrees above horizon.
6th: starts 9.04pm, climbs to 54 degrees above horizon.
8th: starts 8.23pm, climbs to 50 degrees above horizon.
Roy Singham, 31 August 2010