From a bright comet to zodiacal light, we’ve made a list of all the remarkable sky events for this month. Keep reading to find out more!
Astronomical events in September 2023
We provide event dates in Greenwich Mean Time. For your location, the exact date may differ. To find out the time of the event at your location, use the Sky Tonight application.
- September 1: Aurigids’ peak (ZHR = 6).
- September 3: Moon passes 3°05' from Jupiter (mag -2.6).
- September 4: Venus ends retrograde motion; Jupiter begins retrograde motion.
- September 5: Moon passes 1°6' from the Pleiades (mag 1.2).
- September 6: Last Quarter Moon; Mercury at inferior solar conjunction.
- September 9: September ε-Perseids’ peak (ZHR = 5).
- September 10: Moon passes 1°30' from Pollux (mag 1.1).
- September 11: Moon passes 10°49' away from Venus (mag -4.8).
- September 13: Moon passes 4°6' away from Regulus (mag 1.4), 5°59' away from Mercury (mag 2.0); C/2023 P1 (Nishimura) makes closest approach to the Earth. 🌟
- September 15: New Moon; Mercury ends retrograde motion.
- September 16: Moon passes 0°35' from Mars (mag 1.7).
- September 17: Moon passes 2°24' from Spica (mag 1.0); C/2023 P1 (Nishimura) reaches perihelion.
- September 18: Venus (mag -4.8) at its greatest brightness. 🌟
- September 19: Neptune at opposition.
- September 21: Moon passes 0°54' from Antares (mag 1.0); lunar occultation of Antares (mag 1.1) (visible from Japan, eastern Russia, Guam, and the Northern Mariana Islands).
- September 22: Mercury at greatest morning elongation; First Quarter Moon.
- September 23: September equinox. 🌟
- September 27: Moon passes 2°38' from Saturn (mag 0.5); Daytime Sextantids (ZHR = 5).
- September 29: Full Harvest Moon (Supermoon). 🌟
Planets in September 2023
Mercury (mag -0.8) is in Leo in the morning, low above the eastern horizon. It will be visible for no more than an hour from the middle to the end of the month. Venus (mag -4.8) will be in the east in the morning, first in Cancer and then in Leo. The planet reaches peak brightness this month and will be perfectly visible in the sky. See Mars (mag 1.7) in the evening, very low above the western horizon in Virgo for no more than an hour. Jupiter (mag -2.5) is visible in Aries from midnight until morning. Saturn (mag 0.6) is in Aquarius all night at the beginning of the month. Then, in the middle of the month, the planet is visible from evening to night. Grab a pair of binoculars or a telescope to see dimmer Uranus (mag 5.6) in Aries and Neptune (mag 7.8) in Pisces during the night.
Mercury (mag -0.8) can be seen mid-month in the morning, near the eastern horizon in Leo. Venus (mag -4.8), at its brightest this month, is in the northeast in the morning, first in Cancer, then in Leo. Mars (mag 1.7) can be found in the evening, low above the western horizon in Virgo for no more than an hour. Jupiter (mag -2.5) is visible all night and morning in Aries. Saturn (mag 0.6) is visible all night in Aquarius. Uranus (mag 5.6) is in Aries, and Neptune (mag 7.8) — in Pisces, all night. Uranus and Neptune are faint planets, so you’ll need binoculars or a telescope to see them.
Constellations in September
For those watching from the Northern Hemisphere, well-placed constellations in September include Cygnus, Delphinus, and Corona Borealis. If you’re in the Southern Hemisphere, your top picks for September’s constellations are Capricornus, Microscopium, and Indus.
We could go into the nitty-gritty of how to track down these star patterns by other stars, but let’s face it — spotting small constellations like Delphinus or Indus can be tricky, especially for beginner stargazers. That’s where technology comes to the rescue! You can make things easier by using a stargazing app, such as Sky Tonight, to navigate the night sky.
All you need to do is open the app, type in the name of the constellation you’re trying to find, and tap the target icon next to the matching result. Voila! The app will immediately show you exactly where that constellation is located in the sky for your specific location. And if you’re curious to learn more about what you’re looking at, just tap on the object’s name to get all the details you need. With this tool, you can explore the wonders of the night sky like a seasoned pro.
September Equinox 2023: first day of a new season
This year, the September equinox falls on September 23 at 06:50 GMT (02:50 a.m. EDT). At this time, neither of the Earth’s hemispheres will be tilted towards or away from the Sun. As a result, both hemispheres will receive almost the same number of hours of sunlight. This is why this day is popularly known as the day of equal day and night (read our dedicated article to find out why this isn’t quite true).
The September equinox brings autumn to the Northern Hemisphere and spring to the Southern Hemisphere. After the equinox, the Earth’s Northern Hemisphere gradually tilts away from the Sun, causing temperatures to drop, plant life to slow down, and other signs of autumn to appear. Find out why we have seasons in our dedicated article.
Equinoxes and solstices aren’t events observable from the Earth — you can only see their after-effects. To find out the science behind them, and the interplay between the Earth’s orbit, celestial equator, and ecliptic, watch our 40-second video.
And if you’re confused about the difference between equinoxes and solstices, take a quiz. You might not get 10/10 on the first try, but here’s a hint — start the quiz again for a better result and new questions!
Around equinoxes, you can spot the curious phenomenon called the zodiacal light. It looks like a hazy pyramid of light located above the sunrise or sunset points on the horizon.
Not to mistake it for the light of the nearby town, remember that in autumn, the zodiacal light appears just before dawn. In spring, it can be seen just after dusk. So in September, Northern Hemisphere observers should look for the zodiacal light in the morning, and Southern Hemisphere observers in the evening. If you’re lucky enough to live in tropical latitudes, you can see the zodiacal light all year round!
The source of the zodiacal light is the dust orbiting our Sun in the inner Solar System. Sunlight reflects off the dust grains to create this beautiful light effect. Find out where these dust grains come from and how to tell the zodiacal light from the Milky Way in our dedicated article.
Equinox Full Moon
This month’s Full Moon will occur on September 29, at 09:57 GMT (05:57 a.m. EDT). It will be the first Full Moon of the new season and the closest one to the equinox. In astronomical terms, it’s also considered a Supermoon.
Near the autumnal equinox, the Full Moon rises much faster than usual, because this is when the angle of the Moon’s orbit relative to the Earth’s horizon is at its minimum. For several nights in a row, a large Full Moon rises shortly after sunset. The extra light extended the evening working hours for farmers, that’s why it’s called a Harvest Moon.
While observers in the Northern Hemisphere can enjoy the faster-rising Full Moon in September, those in the Southern Hemisphere can see this phenomenon around the March equinox.
Meteor showers in September 2023
Only three minor meteor showers will peak in September — the Aurigids on September 1, the September Epsilon (ε) Perseids on September 9, and the Daytime Sextantids on September 27. At maximum, they produce about 5 meteors per hour.
The Aurigids are the most powerful of the above (ZHR = 6), but at their peak, the Moon will be 98% illuminated and is likely to outshine the meteors. During the peak of the September Epsilon Perseids, the Moon will be 27% illuminated, providing better viewing conditions. But don’t confuse the September Epsilon Perseids with the August Perseids! The September stream is much weaker. You can read more about these two meteor showers in our dedicated article.
The Daytime Sextantid meteor shower occurs during the day (hence the name), as its radiant point is close to the Sun. Most of the meteors are washed out by the sunlight, but you can catch some “shooting stars” in the twilight before the Sun is fully up. Look for them around 4 or 5 a.m., when the Sun isn’t blocking the view. Learn more about astronomical events that can be visible during the daytime.
Comets in September 2023
Here are some of the best visible comets this month. To observe most of them, you’ll need at least powerful binoculars or a telescope. To locate these comets in the sky, use the Sky Tonight app.
The spotlight of September is the newly discovered comet C/2023 P1 (Nishimura). It was first discovered on August 15, 2023, and is rapidly brightening. By the time it passes the closest point to the Sun on September 17, it should have a magnitude of 1.8, which is brighter than the “green comet” C/2022 E3 (ZTF). The downside is that the Nishimura comet is too close to the Sun in our sky. So start observing it around September 7, when it will be a bit further from our star. At around magnitude 5, it will be visible to the naked eye from dark locations, favoring the Northern Hemisphere. Find it a few hours before dawn in the constellation Leo. We have published an article listing all you need to know about comet C/2023 P1 (Nishimura).
In September, keep an eye out for 2P/Encke. This comet has a very short orbital period of 3.3 years. The 2023 apparition is not the best, but the comet should be visible low in the east from the Northern Hemisphere a few weeks before perihelion on October 22. After perihelion, it will remain too close to the Sun. The predicted brightness varies: Gideon van Buitenen predicts a magnitude of 4.2 at perihelion, the Minor Planet Center — a magnitude of 4.9, and Seiichi Yoshida forecasts a magnitude of around 8. Let’s hope for the best!
September is your last chance to see C/2021 T4 (Lemmon) this year. This comet reached its closest point to the Sun in July and is now fading away. It resides very low above the horizon for observers in the Northern Hemisphere and rises higher for those in the Southern Hemisphere. In September, it will have an apparent brightness of 10–11.
Another comet that should have a magnitude of 10 in September is 103P/Hartley. This comet returns to the Solar System every 6.5 years, and its appearance in 2023 will be a favorable one. The comet will approach our planet at 0.39 AU at the end of September, just before perihelion on October 12. According to Gideon van Buitenen, 103P/Hartley could brighten to magnitude 7.5 around perihelion, meaning it will be visible with binoculars from dark locations. The comet will be visible from both hemispheres but will be higher above the horizon for Northern Hemisphere observers in September-October.
How to navigate the night sky?
Want to discover objects in the sky, like stars and planets? Try out the Sky Tonight app on your phone. It’s like a map that shows what’s up there when you look up. And guess what? You don’t even need the internet once you get on your phone. So, if you’re camping or hiking, it still works.
Just open the app, point your phone at the sky, and it tells you the names of constellations, stars, and more. And if you want to get really good at knowing what’s in the night sky, there are videos that can teach you how to use the app.
In September 2023, there are some really cool things happening in the sky. You can check out super bright Venus, look for a naked-eye visible comet, watch the Moon and planets hang out together, see the zodiacal light, enjoy nights with a Super Harvest Moon, and welcome the new season. And to help you make sense of it all, don’t forget to use the Sky Tonight astronomy app so you never feel lost among the stars.