The Sky at Night
The Milky Way crosses the sky in September from north-east to south-west passing through the constellations of Cassiopeia, Cygnus and Aquila and it is worth seeking a dark location on a moonless night to enjoy this spectacular band of light in the sky. Let your eyes adapt to the darkness and you should be able to see dark areas within the Milky Way which denote areas of gas and dust which block the light from the stars beyond. Cygnus, the Swan, is high in the night sky, an apparent cross shape with Deneb, the brightest star, at the swan's tail and Albireo at the tip of its beak. A small telescope will show Albireo as a double star with one of the stars a golden yellow and the other a beautifully contrasting blue.
Cygnus is home to some very interesting deep sky objects which can be seen with a small telescope. Just to the left of Deneb is a large area of gas and dust which can be seen even with binoculars. Looking like a faint patch of light, this area is transformed in photographs into a likeness of the shape of Mexico and Central America and because of this is popularly known as The North America Nebula. This nebula is at a distance of 2,600 light years and is a place of new star birth which is being illuminated by some of the bright, hot young stars within the gas cloud.
Just beyond the left hand star which forms the cross of Cygnus and marks the Swan's left wing is a fascinating object known as the Veil Nebula. It is only possible to see this nebula with a telescope and ideally with a special filter. The Veil Nebula is the remains of a supernova which exploded about 15,000 years ago and is at a distance of 2,400 light years. Photographs today show the expanding nebula with rope-like or lace filaments. Parts of this nebula were first discovered in 1904 by Dundee's own Williamina Fleming.
September is the month of the autumnal equinox when the Sun crosses the equator and heads into the sky of the southern hemisphere. This crossing will occur on the 23rd September at 7am and will result in a gradual shortening of hours of daylight in the northern hemisphere. One consolation may be that, at this time of year, the Sun's north pole is tilted towards the Earth. This means that we may receive stronger and more frequent bursts of the solar wind around the equinox and, with the Sun becoming more active, this may be a time when we might be fortunate enough to see an auroral display. Reported aurorae show clearly that there are more displays in March and September than at any other time of the year.
Mercury is to the west of the Sun and will be seen before sunrise low towards the east from mid-September until the end of the month. It will only reach about 10 degrees elevation at best before swinging back towards the Sun.
Venus is higher and more westerly than Mercury but being considerably brighter it will be quite obvious in the east before sunrise during September when it will reach 25 degrees elevation before fading into twilight.
Mars sets shortly after the Sun in early September but then moves eastwards towards the Sun and will not be visible throughout the month.
Jupiter rises at 10pm and is highest in the sky, due south, at around 5am at an elevation of almost 50 degrees. The planet will continue to be visible throughout the year and by November will be at its best.
Saturn rises at 8.30pm and will be at its highest elevation in the south at 1am. With its long 29 year orbit of the Sun it has been very low in the northern sky for a few years but is gradually gaining elevation and will reach 23 degrees this year.
The Moon is at last quarter on the 6th, new on the 15th, at first quarter on the 22nd and full on the 29th September.