I hope you have been enjoying some of the clearer evenings we have had with the Summer Triangle prominent high in the sky and with Cassiopeia rising higher as The Plough drops lower towards the horizon.
The following chart represent the night sky at 11.00pm BST on the 8th of September and at 10.00pm BST on the 23rd September. To use the chart, face your southern horizon at the appropriate time and you will see the stars in the chart.
The chart looks a bit messy but The Summer Triangle and part of Cassiopeia are included just to help us find our bearings. This month we are concentrating on the constellation Pegasus- The Winged Horse. The constellation Andromeda- Princess Andromeda, daughter of Queen Cassiopeia and King Cepheus in Greek mythology, is included but we shall say more about that next month.
So facing south, look upwards to your zenith and to the right hand side there is the bright star Deneb, the tail of Cygnus the swan, and further to the right the even brighter star, Vega, which enables us to pick out The Summer Triangle with Altair closer to the horizon.
Enjoy that for a moment then identify Cassiopeia to your east. You should now be able to pick out the asterism, the Great Square of Pegasus, lying south of Cassiopeia and to the east of The Summer Triangle. The stars aren’t particularly bright but they are away from the Milky Way in an empty area of the sky. The Great Square is part of the constellation, Pegasus- the Winged Horse in Greek mythology, but like many constellations it is difficult to make out the image which it is meant to represent and there is nothing which looks like wings. Let us not quibble that The Square isn’t actually a square or that the star, Alpheratz, at the top of the square isn’t even in Pegasus! The important point is that The Great Square of Pegasus gives us another signpost in the sky. The stars, Markab and Scheat, are similar in brightness with magnitudes of 2.5 and 2.7 respectively, but the former is a blue-white star while Scheat is a red giant variable. The final star, Algenib, is marginally dimmer at magnitude 2.8.
Something to look out for
Planets aren’t usually shown on the chart because they move slowly against the starry background but Saturn passed opposition at the middle of last month and Jupiter will be at opposition on the 26th of this month and they are both in the area of the sky discussed above. The planets have been missing from our evening sky for some time so it is good to have them back in good viewing locations. Saturn and Jupiter are in Capricornus and Pisces respectively but these constellations have relatively faint stars so find the correct area in the sky using the Great Square of Pegasus and the Summer Triangle and with magnitudes of 0.4 and -2.9 you can pick out the two planets fairly easily any time throughout the month because they outshine anything in their locality. On Thursday 8th there is a close approach of Saturn and a bright gibbous Moon and Jupiter has a similar close approach on Sunday 11th.
For those of you who are really keen and don’t mind staying up into the ‘small hours’ there is the added bonus of catching Mars as well. It will be lying a good distance further east in the constellation Taurus and best observed after midnight but shining at magnitude -0.2 it would complete a planetary parade!
Finally on Friday 23rd the Sun crosses the celestial equator, marking the autumn equinox in the northern hemisphere, and after which there will be more hours of darkness than daylight.