This Week’s Sky at a Glance, March 12 – 20 – Sky & Telescope


■ Spot Arcturus, the Spring Star, glittering pale yellow-orange very low in the east-northeast after nightfall. It climbs higher in the east later in the evening.

By modern measurements Arcturus is visual magnitude –0.05, making it the fourth-brightest nighttime star. It’s bested only by Sirius, Canopus, and Alpha Centauri (counting the combined light of Alpha Cen A and B; they appear as one to the unaided eye).

So for northerners who can never see Canopus or Alpha Cen, Arcturus is bested by Sirius alone. However, Vega and Capella are very close on its heels.

■ February was Orion’s month to stand at his highest in the south in early evening. March pushes him westward and brings his dog, Canis Major sporting Sirius on his chest, onto the south meridian.

In a moonless dark sky, the stars of Canis Major can be connected to form a nice dog profile, but through a brighter sky only his five brightest stars show well. These form the unmistakable Meat Cleaver. Sirius and Murzim (to its right) are the Cleaver’s wide top end, with Sirius sparkling on its top back corner. Down to Sirius’s lower left is the Cleaver’s other end, including its short handle, formed by the triangle of Adhara, Wezen, and Aludra. The Cleaver is chopping toward lower right.

■ Want to try for Sirius B, the famous white dwarf? Sirius A and B are now at the apparent widest apart of their 50-year orbit, 11 arcseconds apart, and will remain so for the next several years before they start closing up again. You’ll want at least an 8-inch scope, a night of really excellent seeing (keep checking night after night), Sirius at its very highest like it is now right after dark, and the Sirius-B-hunting tips in Bob King’s article Sirius B – A New Pup in My Life.

The Pup is east-northeast of the Dog Star and 10 magnitudes fainter: one ten-thousandth as bright. As Bob recommends, put a homemade occulting bar across your eyepiece’s field stop: a tiny strip of aluminum foil held with a bit of tape, with one edge at the center of the field. Looking through the eyepiece, use a pencil point to maneuver the strip into sharp focus. At the scope, hide blinding Sirius A just behind the strip’s edge.


■ The Big Dipper glitters softly high in the northeast these evenings, standing on its handle. You probably know that the two stars forming the front of the Dipper’s bowl (currently on top) are the Pointers; they point to Polaris, currently to their left or lower left.

And, you may know that if you follow the curve of the Dipper’s handle out and around by a little more than a Dipper length, you’ll arc to Arcturus, now rising in the east.

But did you know that if you follow the Pointers backward the opposite way, you’ll land in Leo?

Draw a line diagonally across the Dipper’s bowl from where the handle is attached, continue far on, to go to Gemini.

And look at the two stars forming the open top of the Dipper’s bowl. Follow this line past the bowl’s lip far across the sky, and you crash into to Capella.

■ New Moon (exact at 5:21 a.m. EST).

Daylight-saving time begins at 2 a.m. tonight for most of North America. Clocks spring forward an hour. Tonight there will be no such thing as 2:30 a.m. local civil time.

If in the next seven months the US Congress passes a measure recently introduced to make daylight-saving time permanent, this will be the last time most Americans ever change their clocks, and today’s remaining hours will be the last we will ever have standard time or write EST, CST, MST, or PST. Winter evenings wouldn’t get dark as early, but more of us would get up and off to work or school in darkness, especially in December and January.


■ Return to that triangle of Adhara, Wezen, and Aludra the hindquarters of Canis Major i.e. the handle area of the Meat Cleaver lower left of Sirius. Just left or upper left of that triangle, forming a 3rd- and 4th-magnitude arc, are the three uppermost stars of the constellation Puppis. No, it’s not a puppy, despite following right behind the Big Dog. It’s the Poop Deck (stern) of the giant ancient constellation Argo Navis, the ship of Jason and the Argonauts. These three are the only stars of Argo that are readily visible naked-eye from mid-northern latitudes.

Just 1.4° upper right of the middle of the three, binoculars on a dark night will show the 6th-magnitude open cluster M93. It’s elongated east-west.

The brightest asteroid, 4 Vesta, creeps in eastern Leo at a binocular-easy magnitude 5.9. Use the finder chart with the article about Vesta in the March Sky & Telescope, page 48. If you were to swap Vesta in for our Moon, “the asteroid would look like a baby white potato with an apparent diameter of 4.7 arcminutes, about half the width of the Moon’s Mare Imbrium. But Vesta would look spotlight-bright because it’s nearly four times as reflective as our satellite neighbor.”


■ On the traditional divide between the winter and spring sky is the dim constellation Cancer. It’s between Gemini to its west and Leo to its east. Cancer holds something unique: the Beehive Star Cluster, M44, in its middle.

The Beehive shows dimly to the naked eye if you have little or no light pollution. With binoculars it’s easy, even under worse conditions. Look for it a little less than halfway from Pollux in Gemini to Regulus in Leo.

■ And while you’re working from Gemini to Cancer, consider Ken’s Cancer Cascade, a long asterism of a star line, Kemble’s Cascade style, 2° tall at the Cancer-Gemini border. You’ll want at least a 4-inch scope with its lowest-power eyepiece. See Ken Hewitt-White’s “All Around the Beehive” article, photos, and chart in the March Sky & Telescope, page 54.


■ Bright Sirius, in the south these evenings, is the bottom star of the equilateral Winter Triangle. Its other two stars are orange Betelgeuse to Sirius’s upper right (Orion’s shoulder) and Procyon to Sirius’s upper left. This is the time of year when the Winter Triangle balances on Sirius shortly after dark.


■ By nightfall, the Big Dipper is high in the northeast and beginning to tip left. Look left of its center, by about three fists at arm’s length, for Polaris in the dim Little Dipper. Other than Polaris, all you may see of the Little Dipper through light pollution are the two stars forming the outer edge of its bowl: Kochab (similar to Polaris in brightness) and below it, fainter Pherkad. Find these two “Guardians of the Pole” to Polaris’s lower right by about a fist and a half at arm’s length.

Now is the time of year when the Guardians line up exactly vertically in mid- to late twilight. They’re only 2nd and 3rd magnitude, so use binoculars to pick them out of the deepening blue as early as you can while the stars are coming out.

■ This just in from Wayne Thomas and David Dunham: “Best asteroid occultation of 2021 in s.w. USA, including Phoenix at 9:47 pm MST (& east to Las Cruces, Austin, & Houston) Wed. Mar. 17.” Also parts of Southern California. The star is magnitude 7.2 near Aldebaran on the outskirts of the Hyades; the asteroid is 8 Flora at magnitude 10.9. The occultation will last up to 4.5 seconds. It’s also worth watching and videorecording the star from across most of the continental US and Mexico in case Flora has any small satellites waiting to be discovered. No video capability? Try the drift-scan method with a still photo. Maps, finder charts, and full details are at the link above.


The waxing Moon shines with the delicate Pleiades on the evening of the 18th, then with Mars on the 19th, and between the horn-tips of Taurus on the 20th (for evenings in the longitudes of the Americas). The crescent smiley-Moon is drawn here about three times its actual apparent size.

■ In early evening look for the Pleiades glimmering to the right or upper right of the Moon, as shown above. Aldebaran and Mars shine over the Moon, like two orange eyes over a very tiny smile-mouth (smaller than drawn above). If you were inclined to see this as a face with a personality, what would it be its message to you from up there? Give it a try. That’s what your imagination is for.


■ Now the Moon shines closer above Mars and Aldebaran, as shown above.

■ Pollux and Castor in Gemini pass nearly overhead around 7 p.m. this week if you live in the world’s mid-northern latitudes. They go smack overhead as seen from near latitude 30° N: Austin, Houston, the US Gulf Coast, northernmost Africa, Tibet, Shanghai.

The “twin” heads of the Gemini figures are fraternal twins at best. Pollux is visibly brighter than Castor and pale orange. And as for their physical nature? They’re not even the same species.

Pollux is a single orange giant. Castor is a binary pair of two smaller, hotter, white main-sequence stars, a fine double in amateur telescopes. If Pollux were a basketball, Castor A and B would be a tennis ball and a baseball about a half mile apart.

Moreover, each Castor star is closely orbited by an unseen red dwarf a marble in our scale model with a period of just a few days.

And a very distant close pair of red dwarfs, Castor C, is visible in amateur scopes as a tiny, single 10th-magnitude speck 70 arcseconds south-southeast of the main pair in our scale model, a pair of marbles about 3 inches apart at least 10 miles from Castor A and B.

Read more in Fred Schaaf’s “Gemini’s Like and Unlike Twins” in the March Sky & Telescope, page 45.


■ And now the Moon shines between the horn tips of Taurus, Beta and Zeta Tauri, as shown above. These two stars form a long rectangle with Mars and Aldebaran: a temporary asterism special to mid-March 2021.

■ Earth crosses the March equinox point on its orbit at 5:37 a.m. EDT on this date. This when the Sun crosses the equator (both Earth’s equator and, equivalently, the celestial equator), heading north. Spring begins in the Northern Hemisphere, fall in the Southern Hemisphere. And no, eggs don’t balance today any better than they usually do, in case someone tries to tell you that.


This Week’s Planet Roundup

Mercury, Jupiter, and Saturn have been doing a slow tease very low in bright dawn for the last couple weeks. Now they’re becoming less shy and more ready to catch your attention. Jupiter and Saturn are climbing a little higher and easier to see each morning, while lower Mercury still maintains almost the altitude it’s had for the last two weeks while brightening just a trace.

Look very low in the east-southeast 40 or 30 minutes before sunrise. They form a diagonal line, as shown below; the line changes a little every morning. With a sky this bright, binoculars will help.

Mercury is about magnitude 0.0, Jupiter is mag –2.0, and Saturn is magnitude +0.7.

Venus is out of sight in conjunction with the Sun.

Mars (magnitude +1.1, in Taurus) shines very high in the west after dark. Mars is a very close twin of Aldebaran to its left or lower left, in brightness and almost in color. Which to you looks just a trace redder? They’ll appear closest together (a wide 7°) for several nights centered on March 20th and 21st.

In a telescope Mars is just under 6 arcseconds wide: a bright blob tiny and disappointing.

Uranus (magnitude 5.8, in western Aries) is far below Mars in early evening. Look for it right after dark before it sinks any lower. Finder chart.

Neptune is hidden in the glare of the Sun.

All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world’s mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.

Eastern Standard Time, EST, is Universal Time minus 5 hours. Eastern Daylight Time, EDT, is UT minus 4 hours. (Universal Time is also known as UT, UTC, GMT, or Z time. For all the down-and-dirty details see Time and the Amateur Astronomer.)

Want to become a better astronomer? Learn your way around the constellations. They’re the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential magazine of astronomy.

Once you get a telescope, to put it to good use you’ll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or Jumbo Edition), which shows stars to magnitude 7.6.

Pocket Sky Atlas cover, Jumbo edition
The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and hundreds of telescopic galaxies, star clusters, and nebulae among them. Shown here is the Jumbo Edition, which is in hard covers and enlarged for easier reading outdoors by red flashlight. Sample charts. More about the current editions.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many. The next up, once you know your way around, are the even larger Interstellarum atlas (stars to magnitude 9.5) or Uranometria 2000.0 (stars to magnitude 9.75). And be sure to read how to use sky charts with a telescope.

You’ll also want a good deep-sky guidebook, such as Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger (and illustrated) Night Sky Observer’s Guide by Kepple and Sanner.

Can a computerized telescope replace charts? Not for beginners, I don’t think, and not on mounts and tripods that are less than top-quality mechanically, meaning heavy and expensive. And as Terence Dickinson and Alan Dyer say in their Backyard Astronomer’s Guide, “A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand.”

Audio sky tour. Out under the evening sky with your
earbuds in place, listen to Kelly Beatty’s monthly
podcast tour of the heavens above. It’s free.

“The dangers of not thinking clearly are much greater now than ever before. It’s not that there’s something new in our way of thinking, it’s that credulous and confused thinking can be much more lethal in ways it was never before.”
            — Carl Sagan, 1996

“Facts are stubborn things.”
            — John Adams, 1770


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