Triangle of stars mark last of summer
Autumn’s advance gathers pace throughout the month but does not officially start until the 23rd, which is known as the autumnal equinox. After this darker skies really set in from mid-evening, allowing earlier access to the night sky.
The summer triangle rides high in the sky marked by Deneb in Cygnus the Swan, Vega in Lyra the Harp and Altair in Aquila the Eagle. These three bright stars are easy for beginners to locate, so get yourself a star map (or refer to the diagram in the June 2005 Newsletter) and see if you can identify these. Start with Vega, a blue-white star nearly overhead in mid-evening, and then look south to find Altair and east for Deneb (see August notes). Once these have been located you’ll be able to put some pattern to the jumble of stars in at least one part of the night sky.
Vega appears the brightest star of the three and Deneb the faintest, but appearances are deceptive because of the varying distances of the stars from the Earth. If all these three were placed at the same distance away Deneb would be so brilliant that it would cast shadows and be obvious in daylight. Deneb is actually 1800 light years away – so far in fact that its light takes 1800 years to reach us! Think about that for a moment: we are looking backward in time and seeing Deneb not as it is now but as it used to be in Roman Britain. Therefore it could have exploded 1799 years ago and we would not even know it yet!
September is a relatively poor period for planetary observing, although Jupiter can be seen low down in the south-west after sunset.
The waxing moon can be seen moving away from the sun and western horizon from the 25th to first quarter on the 30th. This is always a great celestial sight when viewed through binoculars or a telescope. The various shades seen with the naked eye suddenly turn into much more detail, including myriad craters. When the moon is advancing to first quarter the relief of the surface is very visible, due to the shadows cast by the angle of the incoming sunlight. Once seen through binoculars or telescope for the first time you will never forget it.
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