What Can I See in the Sky in September 2021?

Now that September is here, the nights are getting noticeably longer again. On 1st September, sunset is 20:16 and by 22:25 it is completely dark. The weather in September is usually still mild enough so that you can go out and observe comfortably, although the nights can get chilly so it’s time to start taking out the heavy clothes again. Wrapping up and keeping warm can be the difference between enjoying a nights astronomy and coming inside early.

Sun and Moon

DateSunrise (Irish Time)Sunset (Irish Time)
Sunrise and sunset times
Moon PhaseDate
New Moon7/09/2021
First quarter13/09/2021
Full Moon21/09/2021
Third Quarter29/09/2021
Moon phases



Mercury is in the evening sky this month but is very difficult to see as it sets very soon after the Sun.


Venus will also be in the evening sky. It will be hard to see but not as difficult as Mercury. Look west after sunset. It sets about 1 hour after the Sun but should be bright enough to see through the twilight.


Not visible this month.


Jupiter remains well placed in September. It has already risen when darkness falls. It will be an unmistakably bright star in the south.


Saturn is visible close to the right of Jupiter, it also has risen before darkness falls. It will be a bright star in the south.

Stars and Constellations

Sky chart for August 2021 23:00 15/09/2021 credit: Heavens above

The above sky chart is for 23:00 on 15/09/2021. You can click on the chart to open a new tab and bring you to Heavens Above. On this website you can generate a custom chart for the time and date you wish. The spring constellations of Leo (the lion) and Virgo (the virgin) are gone with Bootes (the herdsman) now setting in the west soon after sunset.

High overhead are Cygnus (the swan), Lyra (the liar) and Aquila (the eagle). The brightest stars in these constellations are Deneb, Vega and Altair and they make up the Summer Triangle which hangs on high in the sky during September. The misty path of the Milky Way also runs through this area of sky.

In the south at this time of year, is the constellation of Scorpius (the scorpion). This is the direction of the centre of our galaxy, the Milky Way. It never rises very high in the sky from Ireland, but if you look in the direction you should be able to make out that it is almost misty or milky with stars.

The autumn constellations are gaining height in the east early the night and as the night goes on they will rise higher and higher. The great square of Pegasus (winged horse) is visible along side Andromeda (mythical princess). If you live in a very dark location you may be able to see the Andromeda Galaxy with your naked eye. If you have binoculars you will easily pick it out. from the square of Pegasus follow the curve of Andromeda until you get to the T shaped turn. Go to the right here for a short distance to find it. It is the most distant object visible without binoculars or a telescope.

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