Sky Tour Podcast for September 2025

I’m Kelly Beatty of Sky & Telescope magazine, and tonight we’re going on a tour of the stars and planets that you’ll see overhead during September. This month we celebrate the equinox; take note of two eclipses; welcome Saturn to the evening sky; and explore the Summer Triangle. So grab your curiosity, and come along on this month’s Sky Tour.
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If you live in the Northern Hemisphere, by now you’ve surely noticed that the daylight hours are getting shorter. Back in July, the change was oh so subtle. But now we’re losing a couple minutes of Sun each day, more so if you live farther north. So it is with mixed emotions that I tell you that the equinox falls on September 22nd at 2:19 p.m. Eastern Daylight Time.
You probably grew up calling this the “autumnal equinox,” because it marks the beginning of autumn, celestially speaking, for northern latitudes. But this also marks the beginning of spring in the Southern Hemisphere, so to avoid any confusion I always refer to it as the “September equinox.” 
In any case, on this date the Sun momentarily shines directly down on Earth’s equator as it heads south in declination. Equinox comes from the Latin word aequinoctium, meaning “equal nights” — days and nights everywhere are both 12 hours long, and the Sun rises due east and sets due west no matter where you are. 
This equinox also plays a role in how we determine full-Moon names. Usually, the full Moon closest to the equinox falls sometime in September, and traditionally we call that the Harvest Moon. But this month, full Moon is on September 7th, which is rather early and almost exactly 15 days before the equinox. The following full Moon falls on October 6th, at least in the Americas, 14.6 days after the equinox — just barely closer. So that will be the Harvest Moon this year, and one in September is dubbed the Full Corn Moon, a consolation prize of sorts.
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Now, don’t feel bad for September’s full Moon, because on the night of 7th it will plunge directly into Earth’s shadow, creating a total lunar eclipse. You might recall that we had one of these blackouts back in March, which was visible (weather permitting) all across the Americas. But the one this month will be positioned much differently, providing oohs and ahhs across eastern Europe and Africa, all of Asia, and Australia. From western Europe, say, England or Spain, the Moon will rise just after totality is over. And we’ll see nothing from the Americas. Too bad!
Now fast-forward two weeks later, to September 21st, by which time the Moon will have swung halfway around its orbit to create a new Moon. On that date the Sun, Moon, and Earth will line up again, this time creating a partial solar eclipse — and a very deep one at that. Trouble is: the best viewing will be off the coast of Antarctica. But sunrise from New Zealand that day will be spectacular, with 60% to 70% of the Sun’s disk missing.
It’s not unusual for eclipses of the Sun and Moon to occur two weeks apart, and it’s even possible to have three eclipses — two lunars sandwiched around a solar, or vice versa — within a one-month span. That last occurred in 2020, and the next set will come in 2029.
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   “Now, Kelly,” I hear you saying, “that’s all well and good, but I don’t live in Europe or Asia or New Zealand. What’s in the night sky for the rest of us?” Fair enough! If you’re up before sunrise, you can gawk at dazzling Venus down near the eastern horizon and somewhat dimmer Jupiter higher up. You’ll recall that these two brightest planets passed very close to one another last month, and they’ve gradually separated in the sky ever since. One noteworthy date is September 19th, when, before dawn, a thin crescent Moon, Venus, and the bright star Regulus will be stacked vertically within 1½° of sky about an hour before sunrise. Very striking!
Meanwhile, Mercury has wrapped up its nice showing before dawn, and Mars is so low in the west after sunset that you’ll be very challenged to pick it out from the glow of twilight.
So that leaves Saturn, and here the viewing prospects are very good. On September 21st Saturn reaches opposition, meaning it’s opposite the Sun in our sky. So you can expect to see Saturn rising an hour or so after sunset early in the month, and by the end of September you should be able to spot it low in the east during early twilight. There aren’t any bright stars nearby, so you shouldn’t have much trouble picking it out. Or, if you want a little help, wait until the Moon rises on September 8th, and Saturn will be 5° or 6°  to its lower right.
Here's a little fun quiz for you: How many moons do you think Saturn has? 20? 40? Nope, the tally is now 274! Incredible, right? This time last year it only had about half that many, but in March astronomers announced the discovery of 135 new Saturnian satellites. They’re all so tiny — at most a few miles across — that they barely registered on images taken with the world’s most powerful telescopes.  
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Summer might be ending astronomically, but most of summer’s stars can still be seen. Topping the list is the trio of bright stars collectively called the Summer Triangle. Finding them is easy, even if your backyard is hopelessly awash with light pollution. Lift your gaze up, way up, to find a bright star that’s almost directly overhead. That’s Vega [VAY-guh — or some say VEE-guh]. It’s in the constellation Lyra [LIE-ruh], the Lyre, and it’s relatively close as stars go, just 25 light-years away. Vega and its relative closeness to us figured prominently in Contact, one of my very favorite movies.
Astronomers gauge a star’s brightness by a number called its magnitude, and Vega is an important star in this scheme. Some 2100 years ago an ancient Greek astronomer named Hipparchus decided to create a method for organizing stars according to their brightness. He called the most luminous ones “stars of the first magnitude,” and he ranked the fainter ones “second,” “third,” “fourth,” and “fifth” — like the prize order in a contest. The ones that are sixth mark the limit of visibility with the human eye. Modern astronomers have assigned Vega the magnitude of 0.00, thought honestly its brightness varies a little bit over time. Now, it turns out that four other nighttime stars are brighter than Vega, and so their magnitudes are negative. One of them is in the evening sky during September. I’ll reveal its identity in a moment, but look around yourself to see if you can figure which one it is. 
If you’re looking up at Vega, you should also be seeing the other two corners of the Summer Triangle. One is to the south of Vega, by about three times the width of your fist. That’s Altair, and it’s the main star is the constellation of Aquila, the Eagle. The name Altair, an Arabic word, means “the flying eagle” and has been in use since medieval times. 
The third star is about two fists from Vega toward east. That star is called Deneb, a Westernized version of the Arabic phrase for the “hen’s tail.” Deneb does mark the tail of a bird, but it’s a graceful swan, the constellation Cygnus. At the swan’s other end is a medium-bright star called Albireo, Arabic for “the hen’s beak,” and it lies close to the middle of the Summer Triangle. 
In between Deneb and Albireo is a row three stars that mark the Swan’s body. The brightest of these, and the one closest to Deneb, is named Sadr, Arabic for the “hen’s chest,” and from this point you can make out the swan’s wings extending on both sides of its body. If you’re able to get away from city lights and out under a really dark, moonless sky, you’ll see that the Swan is gliding right down the middle of the Milky Way’s softly glowing river of starlight.
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By now you’ve figured out that the Summer Triangle isn’t really a constellation but rather an easy-to-spot trio of bright stars. But it turns out that two small, dim constellations lie inside the Summer Triangle. If you sky is decently dark, you can look for them. The first is called Sagitta [suh-JI-tuh], which is Latin for “arrow.” Slide your gaze one fist higher up than Altair, then look for four stars in a compact horizontal line with two very close together on the right end. That’s the “feather” of an arrow that points to the left. There’s actually a fifth star marking the arrowhead, but it’s quite dim and harder to spot.
The other constellation is close by, tucked directly below Albireo in the head of Cygnus. It’s called Vulpecula, which is Latin for “little fox.” All the stars of Vulpecula are quite faint, so you’ll have to take my word that there’s a celestial fox here. In fact, even though this constellation name has been used since the 1600s, there’s not anything close to being shaped like a fox among these faint stars.
OK, time’s up — have you found the star that’s brighter than Vega? Well, if you look west, well above where the Sun set, there’s a star that looks just about as bright. That’s Arcturus, the anchor star in a constellation called Boötes [bow-OH-teez], and technically it does outshine Vega, but only by 5%. Actually, Vega probably looks like the brighter star — both because it’s overhead, where there’s the least haze, and because Arcturus is slightly reddish.
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That’s about it for this month. If you want more tips for viewing the night sky, check out our website, SkyandTelescope.org, which offers great star- and planet-gazing activities.
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And if you want to explore the solar system and universe more deeply, please do check out the full line of binoculars and telescopes available at Celestron.com.
Sky Tour is a production of Sky & Telescope, a division of the American Astronomical Society, and is produced by me, Kelly Beatty.
Next month we’ll spend a little more time with the Lyre, Eagle, and Swan, and explore the myths and legends surrounding them. Until then, I wish you clear skies.