Perimeter Institute is celebrating 25 years of curiosity, wonder, and groundbreaking research in September, and we’re inviting the public to join us. Get your free tickets to come inside our award-winning building, have conversations with scientists, and take part in science activities for all ages.
Can’t make it to Waterloo? It’s a big, beautiful universe, and there’s plenty to discover, wherever you are. Just look up.
For centuries, humans have become lost in big questions about what’s going on up there in the cosmos. In the 17th century, Galileo famously made use of early telescopes to document and share what he discovered in the night sky. Today, some of those discoveries are observable with a decent pair of binoculars.
Shorter days in fall make for longer nights to watch the night sky. The universe itself provides a wonderful laboratory, and observing the night sky is a great place to start a journey into science. Whether you’re camping out or just have a couple hours to escape city lights, here’s what you might see in the sky in September, 2025. To find exact locations for your time and place, we recommend using an astronomy app or site like The Sky Live or Sky Safari.
September equinox
While you’re waiting for night to fall, you may notice days are getting shorter. On September 22, 2025, Earth will experience the September equinox, when the sun appears directly above the equator. The September equinox marks the official start of autumn if you’re in the Northern hemisphere and the start of spring for the Southern hemisphere. The whole thing happens again, with seasons reversed, in March.
Know what’s cool about this day? Around the equinox, days and nights are approximately equal. The word equinox is derived from two Latin words – aequus (equal) and nox (night).
Got Milky Way?
The Milky Way Galaxy is a spiral galaxy that is home sweet home to Earth. Galaxies consist of stars, planets, and clouds of gas and dust, all held together by gravity. From the ground, the core of the Milky Way looks like a faint “milky” band of light across the night sky, from our perspective out on one of the galaxy’s spiral arms.
September marks the end of Milky Way season in the Northern Hemisphere, so there’s still time to enjoy it before it dips below the horizon. Just find a clear, dark night when the moon is new, so it doesn’t throw off too much light. The new moon on September 21 — when the sun and moon are aligned — will be the darkest sky of the month.
How many stars can you count? The Milky Way contains at least 100 billion stars. Earth is located about halfway out from the Milky Way centre. After September, the Milky Way becomes harder to see at some latitudes, but we can look for it again in Canadian skies in February.
Look for Saturn
Approximately once an Earth-year, Saturn comes to opposition. That means Saturn and the sun align, with Earth smack in the middle. It happens because Earth and Saturn orbit the sun at different rates. Earth orbits the sun every 365 days, but Saturn takes approximately 29.4 Earth-years to complete its orbit.
When Saturn reaches opposition, it’s because Earth has caught up to and passed Saturn. And opposition is great news for skywatchers, because it means Saturn is at its brightest and easiest to see, staying up all night long. If you have a telescope, you’ll notice Saturn’s thousands of rings are nearly edge on at the moment, but will appear very bright in the run-up to opposition.
Venus and Jupiter
Just before dawn in the first few weeks of September, you might spot two more planets, Venus and Jupiter. The two planets —along with Saturn in the west — lie along the sun’s daytime path. If you have access to binoculars or a telescope, you can add Uranus and Neptune to the list. Don’t forget to check your local astronomy guides for specific times when they’ll be most visible.
Want to discover more about what’s happening in the night sky? Dig deeper into the science behind black holes, exoplanets, and the expanding universe through space and astronomy resources from Perimeter Institute.
About PI
Perimeter Institute is the world’s largest research hub devoted to theoretical physics. The independent Institute was founded in 1999 to foster breakthroughs in the fundamental understanding of our universe, from the smallest particles to the entire cosmos. Research at Perimeter is motivated by the understanding that fundamental science advances human knowledge and catalyzes innovation, and that today’s theoretical physics is tomorrow’s technology. Located in the Region of Waterloo, the not-for-profit Institute is a unique public-private endeavour, including the Governments of Ontario and Canada, that enables cutting-edge research, trains the next generation of scientific pioneers, and shares the power of physics through award-winning educational outreach and public engagement.
