December ’24 – Rick’s Picks

All month: the solar system continues to favor evening observers this month, leaving only Mars and Mercury for the sunrise crowd. Mercury is hidden in the Sun’s glare as December opens, reaches inferior conjunction on Dec 5, then emerges into the predawn sky, rising 64 minutes before the Sun by Dec 11 as a mag 2.1 crescent only 10% illuminated and 9½ arcseconds wide. It will rise progressively earlier, brighter, and fuller, with dichotomy occurring Dec 20 and greatest western elongation on Dec 24. It reaches mag -0.4 as a gibbous disk 6 arcseconds wide by Dec 31. Venus is an evening star all month, setting at 7:15 pm as December begins and 8:16 pm as it ends, its gibbous form brightening from mag -4.2 to -4.5 and growing from 17 to 22 arcseconds during the month. Although Mars remains up after sunrise all month, it moves well into the evening time slot, rising at 8:17 pm on Dec 1 and 5:54 pm on Dec 31, brightening from mag -0.5 to -1.2 and growing from 11½ to 14 arcseconds as it heads towards opposition on Jan 15. From Dec 1 to Dec 20 it will be within 4° of the Beehive Cluster (M44). The December 2022 issue of OGT showed you how to observe Mars at opposition; a map of its surface features is included with this month’s charts. Both Mars and Jupiter reach dizzying heights again this month, each of them rising to 70° elevation at some point every night. Like Mars, Jupiter outlasts sunrise as the month opens, but it sets two hours earlier by month’s end. It rises right about sunset on Dec 5 and before sunset the rest of December, hovering around mag -2.8 and 48 arcseconds’ diameter all month. Uranus rises 1¼ hours earlier and precedes Jupiter across the sky, its mag 5.6 disk measuring almost 4 arcseconds wide. Saturn spans about 17 arcseconds’ diameter, wrapped inside its 38 arcsecond rings, and its brightness is about mag +1.0 all month as its evening apparition begins to wind down: it sets near 11:30 pm when December begins but before 10 pm when it ends. Neptune isn’t far behind, its 2 arcsecond disk glowing at mag 7.9 and setting roughly an hour after the ringed planet. Among the asteroids, 15 Eunomia comes to opposition at mag 8.2 on Dec 14. This month’s charts will show you where to find it. It will be within 1° of cluster M36 from Dec 1-6.

Dec 1: the shadow of Jupiter’s little moon Io transits the planet from 8:02 to 10:14 pm CST, followed by Io itself from 8:12 to 10:23 pm.

Dec 2+3: new Moon arrived yesterday at 12:21 am CST, so at 4:50 pm Dec 2 (a half hour after sunset), the Moon will be 40 hours old, 3% illuminated, 2½° above the horizon, and 14° left of the spot where the Sun set. You’ll have to be quick to spot it before it sets at 5:01 pm. It’ll be easier (but still gorgeous) at the same time Dec 3: 2½ days old, 7% illuminated, nearly 10° above the horizon, and 23° left of where the Sun went down. It won’t set until 6:03 pm, giving you more time to tease it out of the gloaming. The bright beacon of Venus will be above left of the Moon both nights, 25° away on the 2nd and 13° on the 3rd.

Dec 3: Jupiter’s moon Callisto passes beneath its planet’s south pole from 11:00 pm to 2:00 am CST tonight – a trick none of the other Jovian moons can perform. It will be directly under the pole at about 12:30 am.

Dec 4: look to the SW between sunset (4:19 pm CST) and moonset (at 7:12 pm) as the 14% illuminated, 3½ day old crescent Moon slides slowly towards the horizon, with bright Venus 2½° to its upper right. Meanwhile, you can watch mag 4.8 star 60 Sagittarii – one of the stars forming the Terebellum asterism – disappear behind the dark edge of the Moon at 5:23 pm. As with all occultations, be sure to start watching at least 10 minutes before then to be sure you don’t miss the show. The star reappears out of the very bottom of the Moon’s bright crescent beginning at 6:12 pm.

Dec 5: the shadow of Europa crosses the face of Jupiter from 9:11 to 11:45 pm CST, followed by Europa itself from 9:18 to 11:49 pm.

Dec 7: Jupiter reaches opposition this afternoon, so its moons now transit ahead of their shadows rather than behind them. Meanwhile, Saturn crosses tonight’s sky just 4° above and behind the first quarter Moon. Between 7:30 and 9:30 pm CST, you can get a glimpse of the ghostly white Lunar X emerging along the Moon’s terminator, roughly midway between the lunar equator and the south pole – then look farther north to spot its companion, the Lunar V. Stay out later to admire the color contrast between ruddy Mars and the mostly blue-white stars of The Beehive cluster (M44) in the same 5° field – then spend some time checking out the red planet’s surface features as it heads towards opposition next month. Finally, turn your attention to asteroid 15 Eunomia, in the same half-degree field with NGC 1931, a small emission/reflection nebula with a tiny collocated mag 11.3 open cluster – in small to medium scopes, the pair resemble a comet, with the cluster as its “head.”

Dec 8: Io transits Jupiter from 9:55 pm to 12:07 am CST, followed by its shadow from 9:57 pm to 12:09 am.

Dec 13: the Geminids meteor shower peaks tonight. It’s usually a prolific shower, capable of producing 120 meteors/hour (ZHR), but tonight a nearly-full (98% illuminated) Moon will rise before sunset and stay up until a half hour before sunrise, reducing the Geminids’ frequency to ho-hum levels below 20 meteors per hour. The shower is active from Dec 4-20, however, so keep an eye out for off-peak streakers throughout the month.

Dec 14: look around 65° up in the SE sky around 10 pm CST to see mag +0.9 Aldebaran (Alpha [] Tauri), mag -2.8 Jupiter, and the full Moon in a straight and equally-spaced line, like a trio of marching soldiers.

Dec 17: mag -0.9 Mars and the 89% illuminated Moon edge closer and closer to each other tonight, but you’ll have to crane your neck to see them at their closest: they’re separated by 2° at 10 pm CST (at 30° elevation), 1° by 1 am (at 62°), a half degree at 2 am (at 69°), and only 17 arcminutes at close approach (3:36 am at 67°).

Dec 21: we reach the solstice at 3:21 am CST, marking the start of another winter. If you’re up early, get your binoculars and look between 4° and 10° above the SE horizon around 6:33 am (40 minutes before sunrise) to spot reddish mag +1.0 Antares (Alpha [] Scorpii) 7° below right of coppery mag -0.3 Mercury.

Dec 22: the Ursids meteor shower peaks tonight. A low-volume shower at best (ZHR 10 meteors/hour), the Ursids are active only from Dec 17-26 and have a sharp one-night peak. The last quarter Moon rises shortly after midnight: until then, you might see 5 meteors/hour from a dark site (and 2 or 3 from the suburbs).

Dec 28: early risers have a treat in store as gibbous mag -0.4 Mercury sits 7½° left of a close (<1°) pairing of mag +1.0 Antares (Alpha [] Scorpii) and the narrow crescent Moon (6% illuminated). The trio form a straight line 8° above the SE horizon at 6:30 am CST (45 minutes before sunrise).

Best wishes to all for a happy and healthy new year, filled with wonders both celestial and mundane!

Rick Gering / December 2024