All the planets of our solar system (except Earth, our viewing platform) appear in a long lineup across December’s early evening sky.
Mercury and Venus begin the month deep in the sun’s glare; emerging from the far side of the sun, they’ll become visible by midmonth from sites with a good view toward the direction of the setting sun, but 30 minutes later. Venus will be possible to see with the unaided eye, and Mercury with binoculars in the same field, as sky darkens a bit.
Watch the moon cozy up to each of the three other naked-eye planets within a 10-day span: Saturn in Capricornus on Nov. 28, Jupiter in Pisces on Dec. 1, and Mars in Taurus on Dec. 7. In a rare occultation of the red planet at opposition and at its brightest (magnitude -1.9), the full moon will actually cover and uncover Mars early that evening.
Uranus and Neptune, discovered in 1781 and 1846, respectively, are fainter and require at least binoculars and a finder chart. It’ll be best to search for them when the moon is absent, or just a crescent and not close by.
The moon returns to the evening sky to sweep past all seven planets in 11 nights, Dec. 24-Jan. 3.
The December 2022 Sky Calendar, the December Evening Skies constellation map and the Uranus finder chart, will help you see the events mentioned in this column and find your way around the sky.
Observers with good-quality telescopes can enjoy views of Jupiter, its equatorial cloud belts, and four satellites discovered by Galileo, as well as Saturn’s rings. Using medium and higher magnifications, try also for a surface feature on Mars discovered in 1659: Syrtis Major, a dark triangular patch of volcanic rock. It passes just north of the center of Mars’ disk on Dec. 1 at 8:48 p.m. One rotation of Mars on its axis takes a bit more than 24 hours, so look for the same feature 36 minutes later each evening—Dec. 2 at 9:24 p.m.; Dec. 3 at 10 p.m., etc.—through Dec. 6 at 11:48 p.m. Continuing, it passes the center of the Martian disk 36 minutes later on the next night, and so on, ending with Dec. 14 at 4 a.m. When our local atmosphere is steady (good seeing), and when Mars isn’t low in our sky, Syrtis Major may be seen for up to two hours before or after these ideal times. Also, if you notice a bright northern edge to the disk of Mars, you may be seeing the North Polar Hood (NPH), a cloud deck above the area above the north pole of Mars. Mars’ northern spring equinox will occur on Dec. 26. In the weeks following, the NPH is expected to dissipate, unveiling the north polar cap of frozen carbon dioxide and frozen water.
At dusk on Dec. 7, the full moon is closely to the upper right of Mars low in the east-northeast, and poised to occult it. Thirty minutes after sunset, Mars appears about one degree to the lower left of moon’s center, or three-quarters of a degree from its edge. From Reno, around 6:37 p.m., the moon takes about 30 seconds to “snuff out” Mars, because the planet is not a point source, but has a sensible disk, at least when viewed with a telescope. Around 7:39 p.m., Mars reappears at the moon’s upper edge.
Using binoculars within 30 minutes after sunset on Dec. 8, try for Mercury 4.8° to the upper left of Venus, very low in the southwest to west-southwest, with the moon rising within 12° to the lower left of Mars in the east-northeast. From a place with unobstructed views in the critical directions—no high mountains—you may be able to spot all six bright members of the lineup, in order from horizon to horizon, Venus, Mercury, Saturn, Jupiter, Mars, and the moon, simultaneously. That’s a 177° span! After Dec. 8, moon rises later and drops out of the early evening sky for two weeks, while Mercury and Venus get easier to see, as both climb higher nightly.
Those folks who enjoy getting out early can follow the moon in the morning sky. It’s near full, in the west-northwest, to the lower right of Mars on Dec. 7, and to its upper left on Dec. 8; waning gibbous, near the “Twin” stars of Gemini, Pollux and Castor, on Dec. 10 and 11; near Regulus, heart of Leo, on Dec. 14; as a crescent near Spica, on Dec. 18; and finally, as a thin, old, 5 percent crescent low in the southeast with Antares, heart of Scorpius, 5-6° to its lower left, on Dec. 21.
Returning our attention to the evening sky, we find Mercury appearing farthest (5.9°) to the upper left of Venus Dec. 16 and 17; reaching greatest elongation 20° from sun and 5.3° to the upper left of Venus on Dec. 21; and ascending highest in twilight on Dec. 23 and 24.
On Dec. 19, Saturn is midway between Venus and Jupiter, 39° from each.
On Dec. 21 at 1:48 p.m., the sun, in the constellation Sagittarius, the Archer, enters the zodiacal sign of Capricorn, and reaches its southernmost excursion directly over the Tropic of Capricorn in the south Pacific Ocean. This marks the beginning of winter for the Northern Hemisphere. That evening, Jupiter is 90° east of the sun, and is only 1.3° south of the place in the constellation Pisces (called the “first point of Aries”), where the sun will appear at the start of spring.
At nightfall that same evening, a line from Jupiter 3.7° west-southwest (to the lower right) to the 5.5-magnitude star 20 Piscium, extended its own length in a straight line past the star, locates 7.9-magnitude Neptune, 7.4° west-southwest of Jupiter. The star 20 Psc marks the end of the handle of an asterism we call Neptune’s Dipper, composed of six stars of magnitude 4.4 to 5.9, all now within 1.7 to 4.7° west-southwest to south-southwest (to lower right, below, and to lower left) of Jupiter. Neptune’s Dipper is easy for almost any binoculars; for fainter Neptune, we recommend at least 50-mm aperture in dark skies.
Uranus at magnitude 5.7 is a much easier target. On our Sky Calendar Extra Content Page, we describe how to get from the head of Taurus (Aldebaran and the Hyades cluster) to the head of Cetus, the Sea Monster, pictured on our constellation map. Then we trace a star hop from Mu in the head of Cetus to the isosceles triangle of Omicron, Sigma and Pi in Aries, shown on our Uranus finder chart. On Dec. 22, Uranus, in retrograde, crosses the line from Pi to Sigma: 1.5° from Pi, and 0.9° from Sigma, entering the triangle, where it will remain for two months until it comes back out on the same side on Feb. 21.
On Dec. 24, the moon returns to the evening sky as a crescent, in a pretty gathering with Mercury and Venus. That day, note sun’s location in southwest to west-southwest, 38 minutes before sunset. On Dec. 24, Venus follows sun’s path, 68 minutes later. You can also find Venus 8° to the lower right of the 4 percent crescent moon. Binoculars will show Mercury 5° to the right of the moon and 4° to Venus’ upper left.
At dusk on Dec. 25, the 10 percent crescent will be in the southwest, with Venus 21° to its lower right; Mercury 3.5° to Venus’ upper left; and Saturn 12° to moon’s upper left.
On Dec. 26, the 19 percent crescent will appear within 6° to the left of Saturn. The moon is midway between Venus and Jupiter, 35° from each. Mercury is 2.8° to the upper left of Venus.
On Dec. 27 at dusk, the 29 percent crescent moon will be high in the south-southwest, with Saturn and Venus respectively 19° and 48° to its lower right, and Jupiter 21° to the moon’s upper left. Mercury will be just 2° above Venus. Mars will be in eastern sky, 90° east of the moon.
Mercury passes within 1.5° north (to the upper right) of Venus on Dec. 28, and will fade sharply and drop lower in twilight in month’s closing days. The moon this evening is a fat crescent, 39 percent full, and 7° to the lower right of Jupiter. Watch Saturn creep along in its 30-year circuit around the zodiac: Tonight, Saturn passes 1.3° north of 3.7-magnitude star Gamma in Capricornus, and will pass 1.4° north of 2.9-magnitude Delta Cap, end of the Sea-goat’s tail, on Jan. 14. Before then, Saturn will form an isosceles triangle with the two stars, 1.6° from each, on Jan. 6.
At dusk on Dec. 29, the moon is at first quarter phase, half full, and is located 90 degrees or one-quarter of a circle east of the sun. Jupiter is 7-8° to the west, or right, of the moon at dusk. Mercury is 1.7° to the right of Venus and slightly higher. On Dec. 29 and 30, the moon and seven planets—in order of their positions in the sky from west to east, Mercury, Venus, Saturn, Neptune, Jupiter, the moon, Uranus and Mars—reach their minimum span during this apparition, 135°.
On Dec. 30, the gibbous moon, 61 percent full, is 21° to the upper left of Jupiter. Mercury, fading rapidly as it faces more of its dark side toward us, is within 2.9° to the lower right of Venus.
At dusk on New Year’s Eve, the 71 percent moon has nearly reached the halfway point of the 68° gap between Jupiter and Mars. Bid farewell to Mercury, 4.4° to the lower right of Venus. Sirius, the “Dog Star,” reaches its high point in the south in the middle of the night, halfway in time between sunset on New Year’s Eve and sunrise on New Year’s Day. Check out Robert Frost’s short poem, “Canis Major,” for an enjoyable description of the canine’s trek from east to west across the southern night sky.
The moon completes its sweep past all the planets, appearing 9° to the upper right of Mars at dusk on Jan. 2, and within 4° to the lower left of the red planet on Jan. 3. The full moon will occur on Jan. 6, just 6° from the “Twin” stars Pollux and Castor at dusk.
Venus will become a prominent evening “star” early in 2023, providing wonderful pairings with stars and other planets, and a farewell display of crescent phases in June-July, all to be covered in Sky Calendar. For $12 per year, subscribers receive quarterly mailings, each with three monthly issues. For info and a sample, visit www.abramsplanetarium.org/skycalendar.
Robert Victor originated the Abrams Planetarium monthly Sky Calendar in October 1968, and still produces issues occasionally, including the December 2022 edition. He enjoys being outdoors sharing the wonders of the night sky. Robert Miller, who provided the twilight charts and the Uranus finder chart accompanying this column, did graduate work in planetarium science and later astronomy and computer science at Michigan State University, and remains active in research and public outreach in astronomy.