The night sky in September – equinox stars and hidden constellations

In the sixth of her popular stargazing series, Omara Williams explores the northern sky as the September equinox approaches. She shows how to find the dimmer constellations of Cepheus, Draco and Hercules, while guiding readers through the month’s eclipses, meteor showers, planetary pairings and seasonal change

As the equinox approaches on 22 September, the balance of the year begins to shift. Nights draw in earlier, the air carries the first crisp hint of autumn, and conditions for stargazing become some of the best of the year. The summer constellations are still with us, but slowly they start to give way to the stars of the new season.

Low in the north, the Big Dipper hovers just above the horizon, its familiar shape easy to spot even as it sinks. Overhead, the brilliant star Vega in Lyra gleams almost at the zenith, while nearby the five stars of Cassiopeia form their unmistakable “W”. These bright patterns act as natural signposts, guiding the eye onwards to constellations that are less obvious but no less rewarding. Cepheus, Draco and Hercules may not shine with the intensity of summer’s stars, yet each holds remarkable sights: pulsing giants, ancient nebulae and clusters of countless suns.

To see them at their best, choose a dark location well away from city lights, avoid tall buildings or trees that block the horizon, and allow your eyes at least 20 minutes to adjust to the darkness. With patience and clear skies, September’s heavens reveal treasures that might otherwise be overlooked.

Find Alderamin and Delta Cephei in Cepheus

Look up towards the northern sky and find the familiar “W” shape of the Cassiopeia constellation. Its brightest stars, Caph and Schedar, shine on the top side of the “W.” From Schedar, follow an imaginary line through Caph to reach the next bright star, Alderamin, which is part of the Cepheus constellation.

Although Cepheus is a relatively dim constellation, its shape is easily recognisable, resembling an upside-down square house with a triangular roof. Alderamin, a white star located at the top left corner of the house, is more massive and luminous than our Sun and is situated 49 light-years away.

Alderamin is the brightest star in the Cepheus constellation, but the most famous is undoubtedly the yellow supergiant Delta Cephei, located at the opposite corner from Alderamin, just outside one of the house walls.

Delta Cephei is a remarkable star, known for its consistent changes in brightness. It doubles in brightness, fades to a minimum, and then doubles in brightness again every 5.36 days. This predictable behaviour is significant for astronomers, as it allows them to calculate distances throughout the cosmos. A similar type of star, also known as a “standard candle”, enabled renowned astronomer Edwin Hubble to conclude that the Andromeda Galaxy is a celestial object outside our galaxy, opening new frontiers in our understanding of the universe.

In Greek mythology, Cepheus was the king of Ethiopia. He was married to the beautiful queen Cassiopeia and was the father of Princess Andromeda. Their stories of conflict and triumph are vividly represented in the constellations of the night sky, showcasing their lasting impact on both culture and astronomy.

Find Eltanin and Thuban in Draco

From Alderamin, draw an imaginary line to your left towards the northwest to locate the next brightest star, Eltanin, shining below and to the right of Vega in the Draco (Dragon) constellation.

Eltanin, an orange giant star 148 light-years away, is positioned at the top left corner of a small trapezium-shaped group of stars forming the head of the dragon. You can follow a trail of stars coming off the head and coiling around the Little Dipper, separating it from the Big Dipper.

One of the most interesting stars in Draco is Thuban, a binary system whose primary star is a blue-white giant 309 light-years away. You can find Thuban shimmering just above Mizar, the star at the bend of the Big Dipper’s handle.

In ancient times, around 2830 BC, Thuban was the northern pole star, and it will occupy this position again around the year 21000 AD. The Egyptian Pyramids were built to have one side facing north, with an entrance passage geometrically aligned so that Thuban would be visible at night.

At the heart of the first curve in Draco’s winding star trail lies one of the most visually captivating deep-sky objects ever observed through astronomical telescopes: the Cat’s Eye Nebula. Located approximately 3,000 light-years away, this planetary nebula forms a series of concentric rings of dust and gas around the ejected material from a binary star system in a stunning and complex display of cosmic interaction.

In Greek mythology, Draco fought against the Olympian gods until the goddess Athena defeated him and threw him into the sky, where he remains twisted to this day. Draco also represents the dragon that the hero Hercules killed in one of his legendary twelve labours.

Find the Keystone asterism in Hercules.

From Eltanin, continue moving to your left towards the northwestern horizon to find a seemingly empty patch of the sky below the bright star Vega. Still, as your eyes get accustomed to the dark, you will start to notice the feeble starlight of one of the largest constellations of the night sky: Hercules.

The Hercules constellation is marked at its centre by a trapezoid-shaped pattern that makes it easy for observers to identify it: the Keystone asterism. Formed by four relatively bright stars, the Keystone asterism represents Hercules’ torso, as he stands victoriously on Draco’s head.

The brightest of the four stars that form the Keystone is the yellow-white binary system Ruticulus, located at the bottom left corner of the group and to the right of the brightest star in Hercules, the yellow giant Kornephoros. From Ruticulus, and along the same line forming the Keystone, lies one of the most significant celestial objects in astronomy: the Great Globular Cluster M13.

M13, located 25,000 light-years away, is home to hundreds of thousands of stars, mainly concentrated at its centre. While it can be seen with the naked eye in dark skies, it is best viewed with binoculars or telescopes. This globular cluster is a treasure trove for astronomers studying stellar evolution, as the stars interact, merge, and even form new stars in the crowded environment.

Nearly fifty-one years ago, in November 1974, scientists sent encoded information about humanity and our solar system to the M13 globular cluster using the Arecibo radio telescope in Puerto Rico. This groundbreaking initiative, known as the Arecibo Message, aimed to reach potential extraterrestrial civilisations in our galaxy. Although it will take 24,949 years for the message to arrive, it serves as a symbol of human curiosity and optimism regarding communication with other life forms.

As we continue to explore the cosmos, the question remains: will we ever make contact with other civilisations, and what challenges might await us if we do?

Night Sky Events in September

The month of September brings us some spectacular night sky events: Sun and Moon eclipses, the autumn equinox, Moon and planet encounters and more meteor showers to enjoy.

September 1 – Peak of the Alpha Aurigids meteor shower.

Look towards the northeastern sky below the bright star Capella in the Auriga constellation after midnight. Typically, you can expect to see an average of 9 meteors per hour, but there have been occasions when over 30 meteors per hour were registered.

September 7 – Full Moon (Corn Moon) and Total Lunar Eclipse.

Watch the full Moon rising in the east at 7:30 p.m. The term “Corn Moon” refers to the harvest season for corn in North America. As the Moon ascends, it will be entirely behind Earth’s shadow, resulting in a total lunar eclipse that will cause the Moon to glow in a deep red colour. This unforgettable spectacle will last for an hour and a half, making it an event you won’t want to miss!

September 8 – The Moon and Saturn alignment.

Watch the Moon and Saturn rising together after 8 p.m. in the eastern sky, shining under the Square of Pegasus asterism.

September 9 – Peak of the Epsilon Perseids meteor shower.

Look towards the northeastern sky after midnight, near Algol, the second brightest star in the Perseus constellation, and above Capella, the brightest star in the Auriga constellation. Unlike the August Perseid meteor shower, this event has a much lower rate, only producing up to 5 meteors per hour at its peak.

September 12 – Moon near the Pleiades star cluster.

The waning crescent moon rises in the northeastern sky after 9 p.m. next to The Pleiades star cluster and shining above the bright orange star Aldebaran, in the Taurus constellation.

September 16 – Moon near Jupiter

Watch the thin crescent Moon shining above bright Jupiter and to the right of the twin stars Castor and Pollux in the Gemini constellation during the early hours.

September 19 – Moon near Venus and Regulus

The thin waning crescent Moon shines above brilliant Venus and Regulus, the brightest star in the Leo constellation, in the eastern sky before dawn.

September 21 – Partial solar eclipse

Although not visible from the UK, it’s important to note that on this day, a partial eclipse will occur over the Southern Pacific Ocean. This event will only be visible from New Zealand and Antarctica, but it will be streamed live for online viewers. The next partial solar eclipse visible from the UK is happening on August 12, 2026, when the Moon will cover up to 91% of the Sun’s disc. This 2026 eclipse will be a total solar eclipse visible from western Iceland and northern Spain. Sadly, the centre of the Moon’s shadow will skim past the UK, leaving us just a few hundred miles out of the path of totality, when the Sun is 100% covered by the Moon.

September 22 – Autumn Equinox

The word equinox comes from the Latin aequus (equal) and nox (night), and from this day, days and nights are getting equal in length for everyone across the globe, an event known as the equilux. In London, the equilux will happen on Thursday, September 25.

During the equinox, Earth’s orbital position results in sunlight reaching both the Northern and Southern Hemispheres equally. At the September equinox, the Sun is positioned directly above the equator as it moves from north to south, marking the approach of winter in the Northern Hemisphere.

September 27 – Peak of the Daytime Sextantids meteor shower.

Look towards the eastern sky after 5 a.m. to the right of bright Venus. You can expect to see around five meteors per hour during this time, with fast fireballs creating a unique display in the early dawn. The elusive shooting stars make it more thrilling to observe. Be sure to find a dark location before sunrise for the best viewing experience.

Omara Williams is a nuclear and software engineer whose multi-award-winning debut science-fiction novel, The Space Traveller’s Lover, shot to international bestseller status. Outside of her literary pursuits, she enjoys stargazing and chasing total solar eclipses.

READ MORE: Catch up with all of Omara’s previous articles on stargazing series here.  

Main image: Hristo Fidanov/Pexels