CSTA Classroom Science

California Skies: February and March 2021

By Robert C. Victor and Robert D. Miller

In your sky watching sessions, we suggest that you begin your outdoor session during evening twilight, so you can experience the joy of discovering and identifying the brighter stars as they first appear. You can begin your session as soon as one-half hour after sunset, or even earlier when the Moon or brightest planets are visible, and can continue until you have enough dark-sky time to observe fainter sky objects.

If you are also interested in doing a predawn session, you have to option to begin early enough to allow time to observe a selection of fainter sky objects before twilight begins. In that case, start the session up to 2 hours before sunrise, and continue long enough into twilight to watch some of the brighter stars disappear.

My friend and former colleague at Michigan State University, Mr. Robert D. Miller, has kindly created computer programs and provided us with monthly sky charts tracking daily locations of the five naked-eye planets and the 16 stars of first magnitude or brighter visible from latitude 34° north. Positions of the stars and planets are plotted each day at the moment the Sun is 9° below the horizon, which we have called “mid-twilight”. Locations of the planets are plotted as a separate dot for each day, with larger, labeled bolder dots plotted weekly on the 1st, 8th, 15th, 22nd, and 29th day of the month. Star positions during the course of the month are plotted as continuous tracks, with all stars drifting westward (left to right on the charts) in the course of the month, owing to the Earth’s revolution around the Sun.

For latitude 34° N, the moment of evening mid-twilight occurs 39 to 47 minutes after sunset, depending on the time or year. Morning mid-twilight occurs a similar interval ahead of sunrise. For locations north of lat. 34° N, the same stage of twilight occurs at a longer time from the times of sunset and sunrise, and for locations farther south, twilights are shorter.

Sometimes a star is below the horizon at the start of a month, but makes its first appearance above the eastern horizon during the course of the month, for example Regulus low in ENE to E in evening mid-twilight in February. Sometimes on a chart, you will notice that a star visible low in the western sky at the start of a month sinks below the western horizon in the course of the month.

Illustrated calendar of sky events

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 the Sun for Regulus, heart of Leo the Lion: low in E at dusk, high in S in the 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-March 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 the 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 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 August  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.

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.

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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