Astronomy Guide to the night sky, September 2023



This is the first monthly guide for the 2023 – 2024 session (last will be May 2024) 

With the Newbury Astronomical Society

The chart above shows the night sky at 22:00 on 15th September 2023

Click on the chart to enlarge and click to the side of the chart to close

The chart above shows the night sky looking south at about 22:00 BST on 15th September.  West is to the right and east to the left.  The point in the sky directly overhead is known as the Zenith and is shown (in red) at the upper centre of the chart.  The curved brown line across the sky at the bottom is the Ecliptic or Zodiac.  This is the imaginary line along which the Sun, Moon and planets appear to move across the sky.  The brightest stars often appear to form a group or recognisable pattern; we call these ‘Constellations’.

Constellations through which the ecliptic passes this month are: Libra (the Scales), Scorpio (the Scorpion) Sagittarius (the Archer), Capricornus (the Goat), Aquarius (the Water Carrier), and Pisces (the Fishes).

Prominent in the southern sky is the Summer Triangle that dominates the Summer Sky and was described in detail on the previous pages.  The term Summer Triangle was first suggested by Sir Patrick Moore and is defined by three obvious bright stars: Deneb in the constellation of Cygnus, Vega in Lyra, and Altair in Aquila.  The Milky Way (our Galaxy) flows through the Summer Triangle and passes through Aquila and Cygnus.

The Summer Triangle is bigger than may be expected but once it has been found it is very easy to find again.  See Pages 4 and 5.  As the Summer Triangle is so easy to find it is very useful to use as a starting place for finding our way around the night sky.

To the west (right) of the Summer Triangle and almost overhead is the constellation of Hercules (the Strong Man).  Hercules has a distinctive distorted square shape, at its centre, called the ‘Keystone’.  This is due to its resemblance to the centre stone of an arch or bridge.  The jewel of Hercules is without doubt the Great Globular Cluster, Messier 13 (M13) that can be found in the western vertical imaginary line forming the ‘Keystone’.

It is just visible using a good pair of 9 x 50 binoculars.  The spherical cluster, of about a million stars can be seen using a 90mm f10 telescope but will look even more impressive when using a larger telescope.

To the East (left) of the Summer Triangle is the constellation of Pegasus (the Winged Horse).  The main feature of Pegasus is the square formed by the four brightest stars.  This asterism (shape) is known as the Great Square of Pegasus.  The square is larger than might be expected but once found is easier to find again.

The square can be used to judge the seeing condition of the night sky.  Under perfect conditions about ten stars can be seen inside the square this would indicate a very good night for observing.  If three to five stars can be seen then conditions will still be good.  If fewer or none can be seen then stick to looking at the Moon or planets.  There is a very nice Globular cluster in Pegasus it is known as Messier 15 (M15) and is a lovely sight to see in a medium to large telescope.

The Ecliptic is low in the sky during the summer months so the Moon and planets appear close to the southern horizon.  Saturn is well placed in the south and Jupiter will be well placed later in the night but due to their low altitude will not be at their best for observation this year.  The thick, murky and turbulent air above the horizon will cause the planets to appear quite unsteady.


Mercury is the smallest planet and closest to the Sun.  It rises over the eastern horizon 05:20 about one hour before the Sun so will not be observable this month.

Venus is also in the early morning sky and rises at 03:25 about three hour before sunrise.  It will appear as a very thin crescent and almost as large in diameter as it can be.  So it will be bright but close to the eastern horizon.

Mars is currently located on the other side of the Sun so is almost as far away as it can be so it appears very small.  It is also close to the Sun in the sky so is difficult to see and make out any detail on the surface.

Jupiter is observable for most of the night from about an hour after it rises over the eastern horizon at about 21:00.  Jupiter will be at its best position for observing at about 04:00 when will be due south and a little higher in the sky.  So it will be a little clearer as it will be higher above the horizon and in clearer and less turbulent air.  The cloud markings and the four brightest (Galilean) moons will be visible, even using a smaller telescope, and with the turbulent air just above the horizon.

Saturn is the first planet to rise over the eastern horizon at about 18:45 so it will be seen low in the south eastern sky as soon as it gets dark.  Saturn was at opposition on 27th August.  This was the night when Saturn was due south at midnight 24:00 GMT (01:00 BST) and at its highest point above the southern horizon.  The best time to observe Saturn this month will be 23:00.

Uranus is just observable this month as it was in conjunction with the Sun on 5th May.  It rises in the east just as the sky darkens.  Uranus will be best seen later is the night as it rises higher in the sky.  It will be best at about 04:00 and just before sunrise.

Neptune has rises at about 19:10 so can be in the sky as the Sun sets and at its best in the south at 01:15.  It will be difficult to see in the late summer sky and will need a telescope to see looking like a small blue ‘fuzzy’ star.

The Newbury Astronomical Society is currently commissioning a new website.

Link to Newbury Astronomical Society website: Home – Newbury Astronomical Society

Direct link to full What’s Up (observing guide) September 2023: Whats_Up_September_2023.pdf – Google Drive

To read our monthly magazine click on: 232401 September 2023.pdf – Google Drive

Our next meeting will be at Stockcross Village Hall on Wednesday 20th September 2023 starting at 19:00 until 21:00.


Leave a Reply

Your email address will not be published. Required fields are marked *

Sign up to the free weekly

Penny Post


For: local positive news, events, jobs, recipes, special offers, recommendations & more.

Covering: Newbury, Thatcham, Hungerford, Marlborough, Wantage, Lambourn, Compton, Swindon & Theale