Transient Events That Can Give Us a Good Enough Reason to Get Outside and Do a Little Observing
All month: the pre-dawn sky sees the return of planets this month, gladdening the hearts of early-rising solar system observers. Neptune is first to break the eastern horizon, rising just before 4:30 am as May begins and by 2:30 am as it ends. The blue planet’s tiny 2 arcsecond disk glows at a relatively feeble mag 7.9, making it a tough catch in morning twilight. Look for it towards the end of the month. Saturn is an easier find, rising 20 minutes after Neptune: its disk spans 16 arcseconds and shines at mag +0.9 all month. Mars brings up the rear in the morning planetary parade, rising less than an hour before the Sun on May 1 but 90 minutes before sunrise on May 31, reaching mag +1.2 across its 4 arcsecond disk. It will become a viable morning target around mid-month. Mercury reaches superior conjunction on May 14 and emerges into the evening sky near the end of the month, its gibbous disk sitting 6° above the horizon at mag -1.1 a half hour after sunset on May 25, and 10° up at mag -0.6 by month’s end. Venus continues its late evening frolic, setting after 10 pm when May opens and a few minutes before 11 pm when it ends, its gibbous disk blazing at mag -3.9 and growing from 11½ to 13 arcseconds over the course of the month. Uranus reaches conjunction on May 22 and is hidden in the Sun’s glare throughout May. Jupiter still holds on, setting shortly after 1 am at the beginning of the month but before 11:30 pm at month’s end. Its magnitude slips slightly from -2.0 to -1.9 during May, as its disk appears to shrink from 35 to 33 arcseconds. May begins a year-long season of mutual events among the Galilean moons, but offers little worth seeing this month. As their setting times imply, Venus and Jupiter – the two brightest planets – grow closer and closer to each other over the course of the month, separated by only 8° at month’s end, as they head towards an even closer conjunction in June. We have no easy targets (brighter than mag 10 all month) among the asteroids, but it might be time to start looking out for comet 10P/Tempel (Tempel 2), currently around mag 11 but expected to brighten a few more magnitudes in the coming months as it ambles through prime summer observing territory between Sagittarius and Aquila and into Capricornus. It reached mag 6.5 in 1925, so let’s hope for another bright apparition this time!
May 3: watch the bright (94% illuminated) gibbous Moon rise less than 2° behind ruddy Antares (Alpha [] Scorpii) around 10:30 pm CDT. The pair’s separation gradually widens as they cross the sky, but they’re still only a few degrees apart when morning twilight erases the tableau.
May 5: the Eta Aquarids meteor shower peaks overnight tonight. Never a great show in the northern hemisphere, this year’s peak comes with a bright gibbous Moon (81% illuminated) that will rise shortly after midnight, set in morning twilight, and wipe out most of the action in between. You’ll probably see no more than 3-5 meteors/hour, although this shower is known for producing a fair number of bright fast-movers with persistent trains, so some of them may be worth seeing despite their modest numbers.
May 6: Jupiter’s most distant Galilean moon, Callisto, transits the planet from 9:33 pm until after it sets at 12:47 am CDT. Transits of Callisto are relatively rare: it usually appears to pass above or below Jupiter, due to its large orbit. Callisto has a very low albedo, and looks like the dark shadow of a Jovian moon as it crosses the cloudtops, making it easier to spot than the other moons in transit. While you’re at it, keep an eye on Europa as it disappears behind the planet’s disk at 10:36 pm.
May 13: if you’re up before sunrise (5:32 am CDT), see if you can spot mag +0.9 Saturn: at 4:30 am, it will be 6° above the east horizon, and 6° below a delicate, 16% illuminated crescent Moon.
May 14+15: early risers get a treat on May 14 as mag +1.2 Mars rises at 4:23 am CDT (about an hour before sunrise) just 7° below left of a slim (8% lit) crescent Moon, with mag +0.9 Saturn watching from its perch 10½° to the Moon’s right. On May 15, the red planet and a paper-thin (3% lit) Moon rise in tandem, with Mars 8½° to the Moon’s right, and Saturn keeping an eye on things from 16° above right of Mars.
May 17: new Moon arrived yesterday at 3:01 pm CDT, so at 8:52 pm tonight (45 minutes after sunset) it will be a paper-thin crescent, 30 hours old and only 2% illuminated, perched 8½° above the horizon and almost directly above the spot where the Sun went down. A line from Jupiter (34° above the horizon) through Venus (15° up) will lead you right to it.
May 18: it’s a gorgeous scene as brilliant mag -3.9 Venus squires the slim (8% illuminated) crescent Moon down to the horizon. Take a peek before the pair drop below the edge of the Earth around 10:45 pm CDT.
May 19+20: bright mag -1.9 Jupiter dances with the crescent Moon both nights, forming a triangle with shy mag +1.2 Pollux (Beta [ Geminorum) hoping to cut in, while Venus stands off to the side like a vigilant chaperone, blazing at mag -3.9. Pollux will be above right of Jupiter both nights.
May 20: at 9:02 pm CDT, mag 6.0 star 9 Cancri will slip behind the dark edge of the 24% illuminated Moon. As with all occultations, start watching at least 10 minutes ahead of time so you don’t miss it.
May 22: if you’re up for a challenge, give Mercury a try tonight. At 8:41 pm CDT (a half hour after sunset), the little planet will be 3½° above the horizon, directly above the spot where the Sun went down, glowing at mag -1.4 (which will be surprisingly faint in the evening twilight). If you miss it tonight, don’t give up: it will get higher each passing day until June 10. Later, mag +1.4 Regulus (Alpha [] Leonis) shepherds the 46% lit Moon across the sky. Watch Luna step backwards and gobble up mag 5.3 star Nu () Leonis at 10:00 pm.
May 23: the closest and farthest Galilean moons march across Jupiter tonight. Dark, distant Callisto does it from before sunset until 9:24 pm CDT, followed by hot little Io from 9:17 until 11:34 pm, and Io’s shadow from 10:16 until the planet sets at 11:50 pm.
May 26: Spica (Alpha [] Virginis) escorts the gibbous Moon across the heavens at a respectful 5° distance.
May 30: Jupiter and Venus are less than 10° apart tonight. The two bright beacons come about a degree closer to one another each night from now until June 9, when there’s only 1.6° of space between them. In another close pairing, the almost-full Moon rises at sunset, just 2½° from red Antares (Alpha [] Scorpii). The pair get closer as the night goes on, reaching a separation of only 1° by 4:30 am CDT.
Rick Gering / May 2026
Rick’s Picks May 2026 overrun: more action involving the Galilean moons
May 4: Ganymede disappears behind the disk of Jupiter at 10:06 pm CDT, and does not reappear until after Jupiter sets at 12:54 am.
May 10: Europa nudges the shadow of Io as the two moons pass within 10 arcseconds of each other from 9:37 to 10:48 pm CDT.
May 15: Europa transits the face of Jove from 8:14 pm CDT (nine minutes after sunset) to 11:03 pm, followed by its shadow beginning at 10:20 pm – shortly after Io slips behind the planet’s disk at 10:03 pm. Meanwhile, the shadow of Ganymede makes the same trek beginning at 8:58 pm. Neither shadow completes the trip before Jupiter sets at 12:17 am.
May 16: Io crosses the planet’s disk from before sunset to 9:34 pm CDT, followed by its shadow from 8:21 to 10:38 pm.
May 24: Io occults Europa tonight, but it happens while Europa is out of sight, eclipsed by Jupiter’s shadow. The two moons are still slightly overlapped when Europa emerges from eclipse at 10:27 pm CDT, and they remain within a few arcseconds of each other until Jupiter sets at 11:47 pm.
Mutual Events of the Galilean Moons – May 2026
Events are calculated for Dearborn Observatory, Evanston IL
Like Earth, Jupiter experiences an equinox twice during each of its 11.8 year-long orbits around the Sun. The four Galilean moons – Io, Europa, Ganymede, and Callisto – orbit Jupiter in the same plane. Ordinarily, we see that plane at an angle, so it appears to us that Jove’s moons pass above or below one another when their visual paths cross as they circle the planet. But at Jupiter’s equinoxes, we see the Galilean moons’ orbital plane edge-on, which means they no longer appear to pass above or below one other. Instead, we can see them pass behind and in front of each other in an occultation, or run into each other’s shadows in an eclipse.
Jupiter will reach its next equinox on December 16, 2026. The resulting eclipse season for the Galilean moons begins in May 2026 and continues through May 2027. Here’s what’s on tap this month:
Date Start End Event Impact Dm Notes/Rating
May 10 21:37 22:48 1E2 0.998 0.0 Graze
May 17 19:48 20:19 1E2 0.365 0.4 Sunset 20:08 – x
May 24 21:58 22:37 1O2 0.026 0.6 Partly in planet’s shadow
May 28 19:29 19:41 1E2 0.595 0.2 Sunset 20:17 – x
Start & End: at what time will the event start and end (CDT, 24 hour clock)
Event: which moon will do what to which other moon
1 = Io 2 = Europa 3 = Ganymede 4 = Callisto
O = occultation E = eclipse
Impact: how much overlap will there be between the two disks (in occultations)
or (in eclipses) how much of the disk will be covered by shadow
0 = 100% coverage 1 = just over 0% coverage (graze)
Dm: how much will the moons’ combined brightness drop during the event (magnitudes)
For eclipses, you’ll want to see a drop of 0.3 mag or more
Rick’s Rating: x = not worth setting up for !!! = definitely worth seeing