By Robert Victor and Robert D. Miller

These monthly evening and morning twilight star maps, the December 2020 Sky Calendar and evening sky map, and summaries of sky events for December 2020 through March 2021 are intended to help teachers guide students to follow the seasonal westward progress of the stars; to notice changes in the arrangements of Moon, planets, and stars in the sky. Observation of natural phenomena can be a source of serenity and joy throughout your students’ lives.

In December 2020, Jupiter and Saturn appear strikingly close to each other low in the southwestern sky at dusk! Jupiter’s creeping past Saturn at intervals of about 20 years is the least frequent pairing of naked-eye planets. After their very close pairing just 0.1 degree apart on December 21, 2020, their next conjunction will occur in 2040, and next after that, in 2060. But on both those occasions the planets will get no closer than 1.1° apart. In 2020, we observe their closest pairing since 1623. Students must wait until 2080 to see the two giant planets as closely paired again.

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 Moon and planets with the five stars of first magnitude within the well-known belt of zodiac constellations. 

Sky maps for twilight -- introduction

Illustrated calendar of sky events with post-twilight constellation chart

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Sky events in December 2020

Evening planets (see evening twilight chart for December, above):  Jupiter and Saturn form a striking, close pair in SW sky at dusk, within 2.2° apart on December 1, closing to just over 6 arcminutes (0.1°) apart on Monday, December 21, and reopening to nearly 1.2° apart on December 31. During December 12-29, the two giant planets appear within 1°, easily fitting within a low-power telescope field. Evenings around December 21, higher magnifications give close-up views of Jupiter’s cloud belts, system of four Galilean satellites, and Saturn with rings 21° from edge-on, all within one field! The pairing of Jupiter-Saturn in Capricornus on December 21, 2020 is their closest since their conjunction in Cancer in 1623, and until another in Capricornus in 2080. Jupiter-Saturn pairings occur at intervals of about 20 years, just over two-thirds of the way eastward (or nearly one-third of the way westward) around the zodiac on each successive occasion. At their next two pairings, in Virgo on the morning of October 31, 2040, and in Taurus within 5° S of the Pleiades on the evening of April 7, 2060, they’ll appear 1.1° apart. This month, Jupiter at mag. –2.0 is the brightest evening “star”,  following the Sun over WSW horizon by 3.3 hours on December 1, by 2.3 hours on December 21, and 1.7 hours on December 31. Saturn at mag. +0.6 is about one-tenth as bright.

Mars is high in SE sky at dusk. Fading from mag. –1.1 to –0.2 this month as Earth pulls away, the red planet ranks next in brightness after Jupiter among early evening’s “stars; ”claims first place when Jupiter sets; and then drops back to second when Sirius appears in ESE. During December 1-31, Mars goes 10° east against the faint constellation Pisces. Binoculars help you enjoy these passages: Mars 1.0° S of 4.3-mag. Epsilon Psc on December 4; within 6° N of gibbous Moon on December 23; 4.5° S of 3.6-mag. Eta Psc on December 31; 2.5° N of 4.3-mag. Omicron Psc on January 1, 2021; and 1.6° N of 5.7-mag. Uranus on January 20.

Stars: The Summer Triangle of Vega, Altair, and Deneb is well up in western sky at dusk, and lower as the month progresses. Capella is ascending in NE, while Fomalhaut goes from S to SSW. Aldebaran, at opposition on December 1, begins month low in ENE, ascending into east, making way for the rising of Orion’s Betelgeuse and Rigel (with belt stars between them) in east.

Morning planets (see morning twilight chart for December, above):  Venus, rising 2.2 to 1.5 hours before sunrise, shines at mag. –4 in ESE to SE in twilight. Going east 1¼° daily, Venus passes 1.4° N of 2.8-mag. Alpha Librae on December 3; within 0.2° N of 2.6-mag. Beta Scorpii on December 18; and 5.6° N of 1st-mag. Antares on December 23. Mercury drops into bright twilight early in the month; superior conjunction beyond Sun occurs December 19. Stars: Of winter’s bright stars in western morning sky, only the arch of Procyon, Pollux, Castor, and Capella remains visible by month’s end. Regulus is high in SW, to upper left of the arch. Arcturus is high in east, Spica in SE to SSE, Vega in NE. Deneb appears to lower left of Vega. Antares emerges in SE late in the month.

Planets near Moon. On Saturday, December 12 at dawn, don’t miss 6-percent, old waning crescent Moon 3° upper right of Venus.  On Wed. December 16 at dusk, catch 2.4-day-old, 7-percent young waxing crescent Moon within 5° below Jupiter and Saturn. In this event just five days before the planets’ December 21 closest pairing, Ju-Sa will appear one Moon-diameter or just over half a degree apart! On Wed. December 23 at dusk, see 9-day, 69-percent waxing gibbous Moon within 6° S of Mars.

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Sky events in January 2021

Evening planets (see evening twilight chart for January 2021, above): Binoculars are recommended for following 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 SW to WSW, sinking to the horizon by mid month. Saturn is to the lower right of Jupiter, by 1.3° on January 1, increasing to 2.1° on January 8. Mercury, emerging from the solar glare, is brighter than Saturn but fainter than Jupiter. Our solar system’s innermost planet passes 1.6° S (lower left) of Saturn on January 9, and 1.5° S (lower left) of Jupiter on January 11. Their most compact trio occurs on January 10, while Jupiter is still its highest and brightest member. That evening, Mercury is 1.7° lower left of Jupiter, while Saturn is 2.3° to Jupiter’s lower right and 2.1° lower right of Mercury. By January 12, Mercury is the highest member, with Jupiter 2.3° to its lower right. On January 13, look earlier in twilight, perhaps half an hour after sunset,  to glimpse a thin 1-percent crescent Moon 4° lower left of Jupiter and 5.4° below Mercury. On January 14 at mid-twilight, the 4-percent crescent Moon is higher and easy to see, with Mercury within 8° to its lower right, and Jupiter within 5° lower right of Mercury. Both Jupiter and Saturn are gone after mid month, while Mercury climbs to greatest elongation and its highest altitude at dusk on the weekend of January 23-24. Mercury starts to fade noticeably at month’s end, as it goes through thinning crescent phases.

Mars is very high in southern sky at dusk all month, while moving 15° east against background stars, from Pisces into Aries. At nightfall on January 20, Mars appears 1.6° N of 5.8-mag. Uranus, making the faint planet easy to locate. During January 10-29 they’re within 5° of each other, but be aware of the First Quarter Moon 6° from Mars on the evening of January 20, and the Full Moon lighting up the sky on January 28.

Bright stars at dusk: The Summer Triangle of Altair, Vega, Deneb, in order of departure in W to NW, 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 ESE before losing sight of Altair setting just north of west, and you’ll see the Summer Triangle and the Winter Triangle of Betelgeuse, Procyon, Sirius simultaneously! Also visible is Fomalhaut, mouth of the Southern Fish, in the southwest, to the left of the planetary traffic jam.

Morning (see morning twilight chart for January 2021, above):   Venus, sinking to SE horizon before month’s end, is the only planet visible. A 3-percent crescent Moon will appear just 3° to upper right of Venus on January 11. Stars: Not many of the huge Winter Hexagon of stars remain. Procyon and Capella depart, and the Twin stars Pollux and Castor make it almost all the way down to the NW 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 on February 17-18, so it’s still visible well up in 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 SE. In coming months, watch the bright zodiacal stars Regulus, Spica, and Antares drift over to the western sky as they approach opposition.

In morning twilight on January 13, the Sun is below the horizon in ESE. 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.

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Sky events in February and March 2021

Evening (see evening twilight charts for February and March 2021, above):
Follow the Moon nightly at dusk, from a thin crescent low in WSW on February 12, to Full, low, north of east, two weeks later on February 26. Moving an average of 13° per day against the background of the zodiac constellations, the fat 44-percent crescent Moon passes within 4° S of Mars on February 18. On the next evening, the Moon, 53-percent full and just past First Quarter phase, is located in Taurus, almost midway between Aldebaran and the Pleiades star cluster. On February 23, the 88-percent gibbous Moon is just 4° south of Pollux, the brighter of the Gemini twins. The other twin, Castor, is 4.5° from Pollux. On the evening of February 26, the Full Moon appears within 8° lower left of Regulus, heart of Leo, the Lion. If you enjoy watching moonrises, then plan to catch the one on February 27, when the Moon will come up 10° north of east around the middle of evening twilight.

As March opens, Mars, faded to mag. +0.9, is moving eastward about 0.6° per day against the background of Taurus, the Bull. Look nightly March 1-6, and watch Mars pass within 3° south of the Pleiades star cluster. The view through binoculars will be wonderful!  On March 15 and 16, Mars will be about midway between the Pleiades and Aldebaran, the star marking one eye of Taurus. During March 19-21, Mars passes within 7° north of Aldebaran. Compare the brightness and color of the two objects. Aim your binoculars at Aldebaran, and within the same field of view, you’ll see many fainter stars, another star cluster, known as the Hyades. The brighter stars of the Hyades form a “V” with the foreground, non-member star Aldebaran. Together, the Hyades and Aldebaran form the head of the Bull.

The Moon comes around again through the early evening sky on March 14-28, again progressing from a thin crescent to full. Follow the waxing Moon as it moves through Pisces; Aries; Taurus (including the Pleiades, Aldebaran, and Mars); Gemini (including Pollux and Castor); Cancer (including a faint star cluster known as Praesepe, the Manger, or the Beehive; Leo (including Regulus); and Virgo (including Spica, not yet risen at the time of mid-twilight in late March).

Residents of southern California with a clear, unobstructed view toward due south on a very clear evening might enjoy searching for the star Canopus, the second brightest night time star, ranking next after Sirius. From the latitude of Los Angeles and Palm Springs (34° N), Canopus passes only 3° above the south point of the horizon some 21-22 minutes before Sirius reaches its high point. Before about March 6, Canopus reaches its high point after evening twilight ends, and nearly four minutes earlier daily. You might appreciate having a bit of twilight during your search, allowing you to see your distant horizon landscape to use as a reference, so the few days following March 6 might be best. If you spot Canopus one evening and return to the same site on the following evening, the star will appear in exactly the same place 3 min 56 sec earlier. Don’t wait too many days after March 6, or the sky will be too bright to find the star.

Morning (see morning twilight charts for February and March 2021, above): Since Venus has moved into bright twilight, the zero-magnitude stars golden Arcturus high in SW and blue-white Vega high in ENE to E are the most prominent stellar-appearing objects in February until Jupiter emerges in ESE late in month. Look for these first-magnitude stars: Spica to lower left of Arcturus; Altair and Deneb completing the Summer Triangle with Vega; reddish Antares, heart of the Scorpion, in SSE to S; and Regulus, sinking in W to WNW. Regulus on the night of February 17-18 is at opposition as Earth passes between that star and the Sun. That night, look 180° from Sun for Regulus, heart of Leo the Lion: low in E at dusk, high in S in middle of night, and low in W at dawn. As Regulus appears at opposition, the orbital revolution of Spaceship Earth around the Sun is carrying us away from the Pleiades in evening sky and toward a point just west of the head of Scorpius in morning sky.

Moon at dawn: After Full Moon low in WNW on January 28, look for the waning gibbous Moon near Regulus in W on January 30; near Spica in SSW at dawn on February 2 and 3. Catch a waning crescent Moon near Antares in SSE on February 6. The Moon’s finale for this cycle will be on February 9, when it will appear as a 6-percent crescent very low in SE to ESE.

Here come the planets! Binoculars will be useful as the planets emerge from the solar glare. In mid-February, Saturn, of mag. +0.7, emerges very low in ESE morning twilight. By February 19, Mercury brightens to mag. +1.0 and appears 4.7° to the left of Saturn. By February 23, Mercury has brightened to mag. +0.5. Watch for bright Jupiter of mag. –2.0 rising 4.6° to its lower left and 7.5° lower left of Saturn. That same morning, Mercury reaches its least distance of 4.1° lower left of Saturn, in a quasi-conjunction.

About an hour before sunrise on February 25-Mar. 10, the Moon makes an eventful 2-week trek across the morning sky, passing three first-magnitude stars and three planets. On February 26, the nearly full moon is 5° upper right of Regulus low in W to WNW.

On February 27, an hour before sunup, the Full Moon in west is 12° upper left of Regulus. The same morning, Mercury, brightened to mag. +0.2, attains its highest altitude for this apparition, but it’s still very low in ESE, 3.4° upper right of Jupiter and 5.0° lower left of Saturn. Jupiter and Saturn, less than ten weeks after their very close conjunction, have spread to 8.0° apart.

On February 28, Mercury appears 3° upper right of Jupiter;

On March 2, the waning gibbous Moon appears 5° above Spica, while Mercury has moved to within 2° upper right of Jupiter. On March 4, Mercury appears just 0.6° above Jupiter.

On March 5, the Moon, just over half full and approaching the Last Quarter, appears 5° above Antares in the south, while Mercury appears at its least distance 0.4° to left of Jupiter, and 9° lower left of Saturn.

On March 9, find the 16-percent crescent Moon in SE, with an impressive string of planets to its left and lower left. In order, starting closest to the Moon, are Saturn, Jupiter (the brightest), and Mercury. On March 10, the 9-percent Moon sits below the 3-planet lineup, within 9° lower left of Saturn and 5° lower right of Jupiter. Mercury is 4.5° lower left of Jupiter that morning, while Saturn is just over 9° to Jupiter’s upper right.

After the epic close conjunction of Jupiter-Saturn at dusk on December 21, 2020, the giant planets have reappeared at dawn while spreading apart: 7° on February 19; 8° on February 27; 9° on March 9; 10° on March 16; 11° on March 24; and 12° on April 2. The gap between them in the predawn sky will continue to grow until June 11, when they’ll be 19¾° apart. After passing opposition on the nights of Aug. 1 and 19, respectively, Saturn and Jupiter will approach to within 15.4° of each other in the evening sky on October 24, before resuming their widening separation. As Saturn disappears into the WSW evening twilight glow in late January 2022, it will be some 21° lower right of Jupiter.

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Spring and summer 2021, and beyond

Venus will pass superior conjunction on the far side of the Sun on March 26, and by late spring will begin to be seen at dusk. In November and December 2021, Venus will be very prominent in the evening sky.

In March through May 2021, Mars, though much faded from its former glory of October 2020, will still be easy to see in the evening sky, moving against interesting background stars of Taurus and Gemini, including the Pleiades, Aldebaran and the Hyades, and Pollux and Castor. We hope you’ll be watching! On the evenings of July 12 and 13, 2021, Venus will appear very close to Mars.

On August 1 and 19, 2021, the Earth will overtake Saturn and Jupiter, and those showpiece giant planets will be up all night, remaining visible evenings for nearly half a year thereafter. That means that in the last five months of 2021, Venus, Jupiter, and Saturn will all be available for evening naked-eye and telescopic observation. I hope that conditions will then be right for teachers and students to get together to share and enjoy the wonderful views.

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Robert C. Victor originated the Abrams Planetarium monthly Sky Calendar in October 1968, and still produces issues occasionally. For subscription information and a sample, visit www.abramsplanetarium.org/skycalendar/

Evening and morning twilight sky maps by Robert D. Miller, who did graduate work in Planetarium Science and later astronomy and computer science at Michigan State University. He remains active in research and public outreach in astronomy.

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