Stargazing Challenges - October 2025
- 22nd Sep 2025
- Author: Dhara Patel
Each month, we'll be sharing a trio of stargazing challenges for you to try your hand at.
This October, look out for the Moon and Pleiades star cluster appearing close together, see if you can spot the Keystone asterism - an easily recognisable pattern of stars, and try to find the M13 Globular Cluster hiding in the constellation of Hercules.
Challenge 1 - Moon and Pleiades
On 9 October, can you catch the Moon beside the Pleiades?
Look towards the east during the late evening of 9 October to catch the waning gibbous moon close to the Pleiades star cluster. Both should be visible to the naked eye, providing you have clear skies. In the hours before midnight, they should be high enough in the sky making the pair easy to spot without obstacles that could obstruct your view.
The Pleiades is an open star cluster – a group of a few hundred newly-formed stars. These hot blue stars are only about 100 million years old – astronomically speaking, they’re infants! Having all formed from the same cloud of gas and dust, over time these siblings will disperse due to the gravitational influence of other stars and structures in our galaxy. Test your eyesight by seeing if you can spot seven individual points of light with the naked eye – it’s why the Pleiades is also known as the Seven Sisters.
It's also a great time to look for details on the Moon during is gibbous phase. In fact, the dark grey patches known as mare often look flat when the Moon is fully illuminated, but look towards the top right edge of the Moon on 9 October and you may be able to see that Mare Crisium looks three-dimensional with lots of detail. This is because the terminator (the boundary between the light and dark parts of the Moon) lies over it, and shadows appear more prominent.
The Moon and Pleiades will begin rising above the horizon shortly after 19:00 and will appear to move closer together as the night unfolds. It might be tricky to spot the Pleiades after midnight as the light of the almost adjacent Moon may outshine the star cluster. Therefore, they’re probably best viewed around 22:00.
Challenge 2: Keystone asterism
On 16 October, are you able to spot the Keystone asterism?
Facing in a westerly direction around 20:00 on 16 October, try looking for a familiar star pattern in the constellation of Hercules known as the Keystone asterism. It will be visible throughout the month but towards the end of the month it’ll appear closer to the horizon when viewing at the same time.
Hercules is the Roman name for the Greek demigod, Heracles, famed for his mighty strength and courage. The constellation is best seen in the night sky between the spring and autumn in the UK and is the fifth largest of the 88 constellations identified by the IAU – International Astronomical Union. Hercules can quickly be recognised by spotting four stars in a lopsided square shape that make up the torso of the hero – known as the Keystone asterism. It gets its name from an architectural term - a keystone is the central stone at the top of an archway that holds the whole structure together.
The star in the bottom right corner is called Zeta Herculis and following round clockwise, is Epsilon Herculis, Pi Herculis and top right is Eta Herculis. Zeta Herculis is actually a double star system made up of a yellow-orange subgiant star and a yellow dwarf star (a bit like our Sun), orbiting each other every 34.5 years.
The star system is 35 light years away, and due to its relatively close distance, it can be resolved or separated into its two parts by any budding astronomer with a medium-aperture (sized) telescope. And because the components of the system are widening, reaching a maximum separation, they’ll be easier to view through amateur telescopes in 2025.
Challenge 3 - M13 Globular Cluster
Are you able to find the M13 globular cluster on 25 October?
Once you’re familiar with spotting Hercules in the night sky, the final challenge of the month is to try and spot a deep sky object within it. On 25 October look towards the west around 19:30 to locate the keystone asterism from Challenge 2. It lies roughly one third of the way along the imaginary line that connect the star Eta Herculis (top right) and Zeta Herculis (bottom right). Again, you’ll be able to look for the M13 Globular cluster throughout the month, but you’ll need to get familiar with the Keystone asterism first to help you lock-in on its precise location.
M13, also known as the Hercules Globular Cluster, is a densely packed group of several hundred thousand stars located roughly 25,000 light years away. To the naked eye on a dark night, it will appear as a fuzzy blob and is one of the brightest globular clusters visible form the Northern Hemisphere. With a pair of binoculars or a small telescope, you’ll be able to resolve a hazy round patch and with a larger aperture telescope, you could even resolve or separate individual stars.
The M13 Globular Star cluster contains the famous ‘blue straggler’ stars which were the target of the 1974 radio transmission known as the Arecibo message. This interstellar message included some basic information about humanity and Earth and was intended to demonstrate how we could initiate contact with potential intelligent extra-terrestrial life. The message has a long journey time though – about 25,000 years!
How did you get on? Were you able to spot our stargazing highlights this month?
If you enjoyed putting your stargazing skills to the test, then keep a look out for the astronomy challenges we'll be sharing each month. And don't forget to share your photos with us using #NSCstargazers
And find out what else you can see this month with our 'What's in the Night Sky' video.
Full references / credits:
(Banner) Skyscape. Credit: © National Space Centre
(1) Moon and Pleiades on 9 October. Credit: © National Space Centre
(2) Keystone asterism on 16 October. Credit: © National Space Centre
(3) M13 Globular Cluster on 25 October. Credit: © National Space Centre
