Transient Events That Can Give Us a Good Enough Reason to Get Outside and Do a Little Observing
All month: Mercury and Mars share the evening sunset this month, but neither of them will be an easy catch. Mercury begins October at mag -0.5 with a 93% illuminated 5” disk, but it sets just 27 minutes after the Sun. By month’s end it sets 51 minutes after sunset – still no easy task, but at least doable – with a 61% lit disk 7” wide, glowing at mag -0.2. Mars sets 63 minutes after the Sun at the start of the month but only 49 minutes after sunset at its end, with a 4” disk at mag +1.5. The evening sky belongs to Saturn and Neptune, which rise together at 6:15 pm as October begins and between 4 and 4:15 pm as it ends. They fit in one binocular field all month, separated by 3¼° on Oct 1 and 4½° on Oct 31. Neptune’s 2½” disk glows at mag 7.8. Saturn’s 19” disk fades from mag +0.6 to +0.9 during the month. The 43” rings flatten from 1.5° to 0.6° from our perspective – only 0.5” thick by month’s end, giving us a chance to see what we missed in March when ring plane crossing occurred while Saturn was lost in the Sun’s glare. The rings begin to re-open in December, and the magic of ringless Saturn disappears until 2038. Meanwhile, Uranus makes its move into the evening timeslot as it nears opposition on Nov 21, rising before 9 pm as October opens and at 6:45 pm as it ends, but still staying up past sunrise. It’s only 4° from The Pleiades (M45) all month, sporting a 4” disk that glows at a binocular-friendly mag 5.6. Mighty Jupiter remains a treat only for night owls and morning people, rising at 12:19 am on Oct 1 and at 10:33 pm on Halloween. During the month, it brightens from mag -2.1 to -2.3 as its disk grows from 37” to over 40” wide. That leaves brilliant Venus, whose morning apparition is beginning to wind down as it rises at 4:42 am when October begins, but not until 5:54 am when it ends. It spends the month almost fully illuminated, its 10” disk gleaming at mag -3.9. Among the asteroids, minor planet 1 Ceres reaches opposition on Oct 2 at mag 7.6, an easy catch southeast of Saturn. This month’s charts will show you where to find it, Uranus, and Neptune.
Oct 3: Jupiter treats us to several double shadow transits this month, starting late tonight from 1:49 to 3:17 am CDT, as Europa’s shadow crosses the planet’s disk from 12:29 to 3:17 am, followed by Io’s from 1:49 to 4:03 am. An even more interesting show is staged by the moons themselves. Io is only 10” behind Europa when Jupiter rises shortly after midnight, but it moves faster than Europa due to Io’s smaller orbit, and when the two moons simultaneously reach the disk at 3:04 am, you’ll need 300x or more to see them as distinct objects. Io then pulls ahead of Europa as the two moons transit. While you’re waiting for the double transit to begin, take a moment to look SW, where mag 5.3 star 42 Aquarii will slip behind the dark (upper left) edge of the gibbous Moon at 1:04 am. As always, start watching several minutes before then, so you don’t miss the star’s disappearing act.
Oct 5: gallant Saturn squires the nearly-full Moon across the sky tonight, hovering protectively just 2° to Luna’s lower right when the pair rise shortly before sunset. They grow more distant as the night goes on, standing more than 5° apart by 4 am. While that’s going on, we’ll also have one final opportunity to see Titan and its shadow march across the disk of Saturn before the rings open enough to block our view of those events. The big moon’s leading edge bumps up against the planet’s disk at 8:25 pm CDT, and 18 minutes later its trailing edge follows suit. Titan reaches Saturn’s meridian around 11 pm. At 11:26, its shadow appears at the very edge ofthe disk, near the north pole. The shadow reaches meridian at 12:38 am, its leading edge exits the disk at 1:17 am, and its trailing edge does so at 1:42 am. Titan itself begins its exit at 1:23 and completes it at 1:44 am.
Oct 9: the gibbous Moon rises 2° ahead of The Pleiades (M45) by 8 pm CDT and harries them across the sky, mowing four of the Seven Sisters down like tenpins. Luna’s first victim is Electra at 10:25 pm, followed by Celaeno at 10:29, Taygete at 10:52, and Maia at 10:54 – but since they disappear against the Moon’s bright limb, you probably won’t be able to see it happen. It’s a different story, however, when they reappear from behind the dark (upper right) leading limb like reborn fireflies: Electra at 11:19 pm, Celaeno at 11:27, Taygete at 11:37, and Maia at 11:55. You’ll need at least binoculars, and preferably a telescope, to watch the show.
Oct 10: it’s another double shadow transit on Jupiter late tonight, but this time the shadows grow closer as the event proceeds. Io’s shadow crosses the disk from 3:05 to 5:53 am CDT and Europa’s follows from 3:42 to 5:56 am, giving us a double shadow from 3:42 until 5:53. The shadows are 7” apart when they first appear, but when the double transit ends there’s less than 1” between them. The two moons move farther apart during this event: at 2:00 am less than 2” separates them, but when Io reaches the disk at 4:57 am they’re almost 9” apart.
Oct 19: we have morning and evening treats today. Early birds can watch the vanishingly-thin (4% lit) crescent Moon rise 4° above right of brilliant mag -3.9 Venus just before 5:30 am CDT. You’ll have an hour to enjoy the view before civil twilight arrives. And if you’re lucky enough to be at a dark site during the next two weeks, be sure to look for the stretched-out triangle of the zodiacal light rising from the east horizon an hour or two before sunrise. Later, at 6:24 pm (20 minutes after sunset), look along the WSW horizon for mag -0.2 Mercury 4° up, with mag +1.5 Mars 1½° above it. Work quickly, before Mercury sets at 6:47 pm. At 12:15 am, you can watch Europa disappear as it moves into Jupiter’s shadow. Night owls see a double shadow transit from 1:24 to 2:18 am, as Io’s shadow crosses Jupiter from 12:04 to 2:18 am, and Ganymede’s does so from 1:24 to 4:28 am.
Oct 20: the Orionids meteor shower peaks tonight, against the perfect backdrop of a moonless sky. The Orionids emanate from Orion’s raised club, and are formed of debris left behind by comet 1P/Halley on its inbound path. They tend to be faint but fast, at 66 km/sec – only the Leonids move more quickly – and they frequently leave persistent trains. Expect to see up to 15 meteors per hour from a dark site, or 5-10 from the suburbs. As with most showers, the best viewing times are between midnight and dawn.
Oct 23: new Moon arrived at 7:25 am Oct 21, and at 6:18 pm tonight (20 minutes after sunset) it will be 2½ days old, 5% illuminated, 3° above the horizon, and 23° left of the spot where the Sun went down. Look for mag -0.2 Mercury 5° above right of the Moon, and mag +1.5 Mars 3° above right of Mercury. Be quick though, because the Moon will set at 6:36, with Mercury (6:44) and Mars (6:50) quickly following it under Earth’s lid.
Oct 24: the crescent Moon crosses tonight’s sky just 1½° below ruddy red Antares (Alpha [] Scorpii).
Oct 27: at 6:30 pm CDT, a fat crescent Moon (33% lit) will step in front of mag 3.3 star Tau () Sagittarii, in the handle of the “teapot” asterism. You’ll need binoculars or a telescope to see it happen.
Oct 28: grab a pair of binoculars or a telescope to see the Lunar X in twilight, on the terminator, midway between the Moon’s equator and its south pole, any time up to 7:30 pm CDT or so.
Oct 30: bright mag 2.8 star Delta () Capricorni winks out behind the dark edge of the gibbous Moon tonight at 7:49 pm CDT. Is it bright enough to see the event naked eye? It pops back out from the bright side at 9:00 pm.
Rick Gering / October 2025