Sky Tour Podcast for May 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 May. This month we’ll look for tiny bits of Halley’s Comet; track down four planets; take stock of bright stars in the late-spring sky; and learn what astronomers call all the stars that don’t have names.
So grab your curiosity, and come along on this month’s Sky Tour.
*****
Most of us know about Halley’s Comet, but this famous object hasn’t been anywhere near us since the mid-1980s. In fact, right now it’s out well beyond Neptune, 3¼ billion miles away. But it made a turnaround of sorts in late 2023, and it’s finally starting to move back toward the Sun and Earth.
Each year about this time, planet Earth glides across Halley’s orbit, and when that happens, we run into rocky grit shed by the comet centuries ago. The bits that slam into our atmosphere are tiny — most no more than one-thousandth of a gram. But they arrive at 66 kilometers per second — 150,000 miles per hour! That’s a lot of kinetic energy, which gets dissipated high in the atmosphere as brief “shooting stars.” 
Astronomers call this annual cosmic light show the Eta Aquariid meteor shower, because these crumbs from Halley’s Comet appear to be plow into us from the direction of the constellation Aquarius, and specifically near its star Eta. Now, since Aquarius isn’t in the evening sky right now, to enjoy this shower you’ll need to get up really early on the mornings of May 5th or 6th, say, at 2 or 3 a.m., a couple of hours before dawn. By then the first-quarter Moon will have just set or nearly set, so its light won’t be a problem. And Aquarius is relatively low down in the sky, which reduces the resulting meteor rates. You might see one every 5 to 10 minutes. If you lived in, say Argentina, it’d be a different story. From there, in early May Aquarius is roughly halfway to overhead as dawn begins, so you might expect to see an Eta Aquariid every couple of minutes. 
Hmm, got a bunch of frequent-flier miles you’d like to share?
If you do get up early to watch this meteor shower, or any other date really, you’ll be greeted by dazzling Venus low in the east as dawn twilight begins, with much dimmer Saturn to its upper right. These two planets start the month rather close together, only 4° apart, but they drift farther apart as we get deeper into May. The waning crescent Moon makes a nice pairing with Saturn on the morning of May 22nd, and with Venus on the 23rd.
*****
Not an early riser? Well, there’s still lots to see after sunset. In particular, two of the five bright planets are in the evening sky right now. Most obvious is Jupiter, over in the west at nightfall. The King of Planets has been with us for many months, but now he’s started his gradual exit from the evening sky. Look to the west an hour after sunset. Jupiter is about twice the width of your clenched first above the horizon as May begins, but at month’s end you’ll be challenged to see it at all, very low in the bright glow of twilight.
The other planet in view is Mars, which you can spot pretty easily. It’s well to the upper left of Jupiter, about halfway to overhead and sitting in a somewhat isolated patch of sky without any other bright stars close by. A very fat crescent Moon makes a dramatically close pass by Mars on the evening of May 3rd, and then again (though not as close) at month’s end. 
We can use Jupiter and Mars to navigate our way to some of the evening’s bright stars and constellations. Are you ready for some stargazing? Then let’s go!
*****
At nightfall in early May, the western half of the sky is littered with bright stars. For example, to Jupiter’s upper right is the bright star Capella. To Jupiter’s upper left, about halfway to Mars, are Castor and  slightly brighter Pollux, the Twins of Gemini. At this time of year these celestial siblings are oriented so they’re standing upright in the sky. To their immediate left is Procyon, the alpha star in Canis Minor, the Little Dog. Slide your gaze toward lower left for a bright beacon just peeking over the southwestern horizon. This is Sirius, the brightest star in the nighttime sky. To its right, below the Twins and halfway to Jupiter, is Betelgeuse, one of the final bits of Orion to remain in view as we pivot toward June. All of these stars are the last vestiges of wintertime constellations that are past their expiration dates and sinking into the western twilight.
Much higher than all of these, about two-thirds of the way to overhead, is Regulus, the alpha star in the constellation Leo, the Lion. Regulus sits at the bottom of a star pattern called the Sickle, because it looks like the hand tool with a curved blade used for harvesting crops. It’s about the size of your clenched fist. Or maybe you’ll see it more easily if you look for a question mark facing the wrong way. In any case, the stars of the Sickle trace out the head of Leo, Regulus marks the lion’s heart, and its body extends off to the left.
Now look to the lower right of Regulus, back to Procyon, and then to its upper right to Castor and Pollux. These stars enclose a big triangle of sky that, apart from Mars, appears fairly empty. But really, it’s not. The triangle’s center marks the location of Cancer, the Crab. This constellation isn’t very big, and it doesn’t have any bright stars. But here’s where you’ll find a star cluster called the Beehive. In a dark sky that’s free of light pollution or strong moonlight, the cluster looks like a soft glow. Binoculars will reveal dozens of individual stars.
*****
We know the brightest stars in the sky by names that have evolved over the last two millennia and which may (or may not) have logical meanings. And the International Astronomical Union has been on something of a tear recently to create new star names, now totaling just shy of 500. But what about all the medium-bright stars that don’t have common names? How do astronomers identify one from another?
Let’s talk about that a bit, using Leo as an example. Regulus means “little king.” The star to its left, at the lion’s back end, is called Denebola, a short form of the Arabic words for “the lion’s tail.” Just above Regulus is Algeiba, Arabic for “the lion’s mane.” Well, that all makes sense. 
However, due to its prominence, Regulus is called the “alpha” star in Leo. In the mid-1500s, German astronomer Johann Bayer assigned a Greek letter to every bright star in a given constellation. The brightest was Alpha, the next brightest Beta, and so forth. By the time he’d finished, Bayer had used this scheme to identify 1,564 stars. So Regulus is also known as Alpha Leonis (the constellation’s genitive form). Denebola is Beta Leonis, and Algeiba (al-JEE-buh) is Gamma Leonis. And earlier you heard me mention the star Eta Aquariid when describing this month’s meteor shower. These Bayer designations cover pretty much all the stars you can see from a location with moderate light pollution, and that’s why you see so many Greek letters on the star charts in Sky & Telescope. 
But what about fainter stars that are still visible by eye? Well, in the 1700s English astronomer John Flamsteed came up with a numerical list for the stars within each constellation. These Flamsteed numbers aren’t based on brightness; instead, they’re sequential from west to east throughout a given constellation. Flamsteed’s system was applied to 2,554 stars — and only for the ones visible from Great Britain!
Astronomers use Flamsteed numbers to identify fainter stars that lack one of Bayer’s Greek letters. But they’re given to brighter stars too. So it’s OK to call Leo’s brightest star Regulus, Alpha Leonis, or 32 Leonis. Take your pick!
*****
Now turn away from Leo and look high up in the northern part of the sky. There you’ll see an obvious star pattern that just about everyone knows: the Big Dipper. You’ll see the Big Dipper looming over you, with its curved handle bent upward and its four-sided bowl apparently overturned as if dumping soup into some imaginary pot.
Even though it’s so well known, the Big Dipper isn’t truly a constellation. It’s what astronomers call an asterism, which is simply any group of stars that make a pattern. The dipper is part of a larger constellation called Ursa Major, the Big Bear. Right now this woolly beast is on its back, with the stars in the Dipper’s handle serving as the bear’s tail, the bowl marking its back, and its head off to the left.
Many constellations and asterisms are chance alignments of stars that lie at different distances from Earth. But the Big Dipper breaks this rule. Five of its seven stars are equally far away, about 80 light-years from Earth. The two exceptions are at the end of the handle and on the lip of the Bowl. What’s more, these five stars are racing in formation across the sky at roughly 28,000 miles per hour. As a result, the Big Dipper’s shape is very gradually changing. In 100,000 years or so, its bowl will flatten out and its handle will bend sharply.
 I think of the Big Dipper as the “Swiss Army Knife of the sky,” because it helps me find so many other key springtime stars. For starters, find the two stars at the left end, forming one side of the bowl. Skywatchers call these the Pointer stars, and here’s why. Draw an imaginary line through the pointers, and follow that line downward by three fists. You’ll come to a moderately bright star. That’s Polaris, the North Star. You can use this little trick anytime you want — just remember that those two stars Point to Polaris.
Are you surprised that the North Star isn’t the brightest star in the sky? In fact, 45 other stars outshine it. But brightness isn’t the North Star’s claim to fame. Instead, it lies very nearly at the point where a line extended out into space from Earth’s north pole would go. So as Earth spins throughout the night, Polaris hardly moves. Now go back to the Pointers in the Big Dipper. Follow that line through them in the opposite direction, up through overhead, and four or five fists later you’ll reach Regulus, the brightest star in Leo. So now you can “Point to Polaris”, and “Leap to Leo”.
But wait, there’s more! Follow the curve formed by the Dipper’s handle until, about three fists away, you reach a very bright star called Arcturus in the east. Arcturus is an ancient Greek star name that means watcher or guardian of the bear. So, congratulations! You now know how to “Arc to Arcturus”.
And did you know that you can even use the Big Dipper to tell time? It’s really easy — to find out how, go to SkyandTelescope.org and type “Star Clock” in the search box. That do-it-yourself Star Clock is just one of many features for beginning stargazers at S&T’s website.
*****
That’s about it for this month. If you want more tips for viewing the night sky, check out “Sky at a Glance” on our website, which offers great star- and planet-gazing activities on a day-by-day basis.
If you haven’t already subscribed, you can find Sky Tour on Apple Podcasts, Spotify, Stitcher, or wherever you listen. And please leave a rating or review! It will help others find the show. 
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.
Join me next month, when we’ll explore the stars found in and near the celestial scorpion. Until then, I wish you clear skies.