The twilight star maps and this summary of sky events for January 2021 are intended to help our readers follow the seasonal westward progress of the stars, and to notice changes in the arrangements of the moon, planets and stars in the sky. Observation of such phenomena has been a source of serenity and joy throughout my life—and I hope to share that with you.
After their historic pairing on Dec. 21, Jupiter and Saturn will still appear strikingly close to each other low in the southwestern sky at dusk. Track them into January’s second week to help find Mercury emerging from the far side of the sun. During Jan. 8-12, Jupiter, Mercury and Saturn form a trio, all fitting within a 5-degree field of view.
The sky frequently offers up pairings of the moon with the five planets whose brightness and motions have attracted attention since ancient times; pairings and groupings of planets; and pairings of the moon and planets with the five stars of first magnitude within the well-known belt of zodiac constellations.
Evening planets: Binoculars are recommended to follow Jupiter and Saturn sinking into bright twilight, and forming a compact trio with emerging Mercury before the giants depart. You’ll also need clear skies and an unobstructed view! Jupiter is very low in the southwest to west-southwest, sinking to the horizon by midmonth. Saturn is to the lower right of Jupiter, by 1.3 degrees on Jan. 1, increasing to 2.1 degrees on Jan. 8. Mercury, emerging from the solar glare, is brighter than Saturn but fainter than Jupiter. Our solar system’s innermost planet passes 1.6 degrees south (to the lower left) of Saturn on Jan. 9, and 1.5 degrees south (to the lower left) of Jupiter on Jan. 11. Their most compact trio occurs on Jan. 10, while Jupiter is still its highest and brightest member. That evening, Mercury is 1.7 degrees to the lower left of Jupiter, while Saturn is 2.3 degrees to Jupiter’s lower right, and 2.1 degrees to the lower right of Mercury. By Jan. 12, Mercury is the highest member, with Jupiter 2.3 degrees to its lower right.
On Jan. 13, use binoculars earlier in twilight, about 24 minutes after sunset, to glimpse a very thin, 1 percent crescent moon, only 20.4 hours after the new moon. Look for the hairline crescent 4 degrees to the lower left of Jupiter, and 5.5 degrees below Mercury. On Jan. 14 at mid-twilight, the 4 percent crescent moon is higher and easy to see, with Mercury within 8 degrees to its lower right, and Jupiter within 5 degrees to the lower right of Mercury.
Both Jupiter and Saturn are gone after midmonth, while Mercury climbs to greatest elongation and its highest altitude at dusk on the weekend of Jan. 23-24. Mercury starts to fade noticeably at month’s end, as it goes through thinning crescent phases.
Mars is very high in the southern sky at dusk all month, while moving 15 degrees east against background stars, from Pisces into Aries. At nightfall on Jan. 20, Mars appears 1.6 degrees north of 5.8-magnitude Uranus, making the faint planet easy to locate. From Jan. 10-29, they’re within five degrees of each other, but be aware of the first quarter moon, 6 degrees from Mars on the evening of Jan. 20, and the full moon lighting up the sky on Jan. 28. Between those dates, watch the waxing gibbous moon pass 4 degrees north of Aldebaran, eye of Taurus, on Jan. 23, and leapfrog past Castor and Pollux of Gemini from Jan. 26 to 27. On Jan. 31, our home Spaceship Earth is racing directly away from Mars by more than 900,000 miles per day, causing the red planet to fade.
Other bright stars at dusk: The Summer Triangle of Altair, Vega and Deneb, in order of departure in the west to northwest, can still be seen in its entirety until mid-January, while the eastern sky is filling up with winter’s bright stars. Try to spot Sirius rising in the east-southeast before losing sight of Altair, setting just north of west, and you’ll see the Summer Triangle and the Winter Triangleof Betelgeuse, Procyon and Sirius simultaneously! Also visible is Fomalhaut, mouth of the Southern Fish, in the southwest, to the left of the planetary traffic jam.
Morning: Venus, sinking to the southeastern horizon before month’s end, is the only morning planet. It rises before the sun, by nearly 1.5 hours on Jan. 1, shrinking to only 40 minutes on Jan. 31. A 3 percent crescent moon will appear just 3 degrees to the upper right of Venus on Jan. 11. This will be your last chance to observe an impressive Venus-moon pairing like this until May 12.
In the morning sky before Jan. 11, watch the waning moon go past Regulus on Jan. 2 and 3, pass north of Spica on Jan. 6, and go past Antares on Jan. 9 and 10.
Stars: Few of the huge Winter Hexagon of stars remain. Procyon and Capella depart, and Pollux and Castor make it almost all the way down to the northwestern horizon. These Twin stars are at opposition to the sun in the second week of January, so you can see them all night, from dusk until dawn. Regulus will be at opposition Feb. 17-18, so it’s still visible well up in the western sky on January mornings.
We find the spring stars Arcturus and Spica crossing high in the southern sky. Spica will be at opposition on April 13-14. Antares, at opposition on May 30-31, is ascending in the southeast. In the coming months, watch the bright zodiacal stars Regulus, Spica and Antares drift over to the western sky as they approach opposition.
In the morning twilight on Jan. 13, the sun is below the horizon in the east-southeast. Spaceship Earth is heading in the direction of Spica. As we curve around the sun, we will pass between Spica and the sun in three months, on the night of April 13, and Spica will be visible all night.
To check for the post-pandemic resumption of star parties hosted by the Astronomical Society of the Desert, visit the club’s website at www.astrorx.org. Rancho Mirage Library’s Observatory is currently closed as well, although the library is open during limited hours; visit www.ranchomiragelibrary.org/observatory.html for updates.
I originated the Abrams Planetarium’s monthly Sky Calendar in October 1968, and still produce issues occasionally. For subscription information and a sample, visit www.abramsplanetarium.org/skycalendar.
Wishing you clear skies!
Robert Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing informal sky watching opportunities for folks in and around Palm Springs. Robert D. Miller 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.