Astronomy guide to the night sky September 2025
With the Newbury Astronomical Society
The chart above shows the night sky at 21:00 on 15th September 2025
(Click on the image above to enlarge and click away from the image to return here)
The chart above shows the night sky looking south at about 21:00 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 is a good place to start to explore the night sky. 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. 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 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. M13 is thought to be the centre of a small galaxy that ventured too close to our galaxy
To the west of Hercules and moving towards the western horizon is the bright orange coloured star called Arcturus in the constellation of Boötes. Arctaurus is a star similar to our Sun but more advanced and is developing into a Red Giant star that is nearing the end of its ‘life’ as a normal star. It has used almost all of its Hydrogen fuel and has expanded to become a Red Giant, 25 times the diameter of our Sun. At the moment it shines 115 times brighter than our Sun but it is destined to collapse and become a White Dwarf and Planetary Nebula.
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 southeast later in the evening but due to its low altitude will not be at its best for observation until later this year. The thick, murky and turbulent air above the horizon will cause the planets to appear quite unsteady.
WHERE TO FIND THE PLANETS THIS MONTH
MERCURY is the smallest planet and closest to the Sun. It is very close to the Sun this month so not observable.
VENUS is very close to the eastern horizon as the Sun is about to rise at about 05:00. It is moving back towards the Sun and its Superior Conjunction on 8th January 2026. Venus is heading back to the Sun in the east at 05:00
MARS is moving further away from us as we on Earth moves faster along our orbit leaving Mars behind.
JUPITER Is well placed for observing in the early hours of morning before sunrise at about 05:00 in the east. It will not be observable in the evening sky until next year.
SATURN in the east but will be better placed later in the evening. It is very close to Neptune. The two planets were close together during August but are now moving a little further apart.
URANUS rises over the eastern horizon about 21:00 but is best observed at about midnight when it has moved into the southern sky and is higher above the horizon.
NEPTUNE is very close to Saturn in the north-eastern early evening sky. It is a good time to find Neptune.
To see a full version of this article and a guide to the night sky with charts, read the monthly magazine on the Newbury Astronomical Society website at: Magazine September 2025
For details and directions visit the Newbury Astronomical Society website at: Home – Newbury Astronomical Society
Our next meeting will be at Stockcross Village Hall on Wednesday 15th September 2025, from 7pm until 9pm.
