This Week's Sky at a Glance, March 22 – 31

Periodic Comet Pons-Brooks has been brightening on schedule and is now about 5th magnitude, near its expected peak of 4.5. That puts it well in range of binoculars in a decent suburban sky, and it may be detectable naked-eye in a black sky. Brightness outbursts are possible; the comet has had two in the last year, so check in on it every clear evening.

Pons-Brooks is fairly low in the west-northwest right after the end of twilight. It's lower right of Jupiter and heading toward it; see the detailed finder chart with the article in the March Sky & Telescope, page 48. Its tail points upward. Next week it should be at its best.

On the evening of March 30th the comet will be passing only about ½° right or lower right of 2nd-magnitude Alpha Arietis (Hamal).

Betelgeuse stops fading. Orion's red supergiant, always a slow variable star, lost 0.3 or 0.4 magnitude (visual) from late January to early March, prompting speculation that another "great dimming" might be starting like the one in winter 2000. But for the last three weeks Betelgeuse has held at about mag +0.7. That amounts to hardly more than its usual slow wobbles. Will it resume fading? Keep watch using Aldebaran and Procyon as your comparison stars.

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FRIDAY, MARCH 22

■ Arcturus, the "Spring Star," now rises above the east-northeast horizon just around the time the stars come out. How soon can you spot it?

Once Arcturus is nicely up, look for the narrow Kite asterism of Boötes extending two fists to its left. The left end of the Kite is bent slightly up. How much of it can you pick out through the moonlight?

SATURDAY, MARCH 23

■ The signature fall-and-winter constellation Cassiopeia is retreating down after dark. Look for it in the north-northwest. It's standing roughly on end. For skywatchers at mid-northern latitudes and farther north, Cassiopeia is circumpolar, never going away completely. By 1 or 2 a.m. daylight-saving time it will be at its lowest in the north, lying like a not quite horizontal W.

■ The Moon is just shades of gray, right? Not exactly! Some areas display very slight color tints. The plainest to me at the eyepiece has always been the slightly brownish lava flow, nicely sharp-edged, that mostly but not quite fills Mare Serenitatis. That area is in fine sunlit view for color judgment when the Moon is waxing gibbous, like now. And check out Tom Dobbins's "Seeing Color on the Moon" in the March Sky & Telescope, page 52.

SUNDAY, MARCH 24

■ If you haven't spotted Mercury yet this season, look for it lower right of Jupiter as twilight fades as shown below. Jupiter is magnitude –2.1. Mercury this evening is magnitude –0.1, meaning one sixth as bright. And that's not counting the extra atmospheric extinction that affects low objects.

■ Full Moon tonight (exactly full at 3:oo a.m. EDT Monday morning the 25th). The Moon rises due east around sunset. By 9 p.m. or so, once the Moon is shining high in the southeast, look below or lower left of it by two fists at arm's length for Spica.

■ This full Moon comes with a deep penumbral eclipse late tonight! You're in luck if you're anywhere in the Americas including Hawaii. "Penumbral" means the Moon passes only through the pale outer fringe of Earth's shadow, the penumbra. Mid-eclipse occurs tonight at 7:13 UT, which is 3:13 a.m. EDT, 2:13 a.m. CDT, 1:13 a.m. MDT, 12:13 a.m. PDT, and 10:13 p.m. Hawaii Standard Time. At that time the Moon's northeast edge will just miss the edge of the shadow's dark umbra. That means this just misses becoming a partial lunar eclipse.

Still, the shading on the Moon's celestial northeast edge will be quite pronounced around mid-eclipse time. Some shading will be visible for well over an hour before and after. World map, eclipse diagram, and other info.

MONDAY, MARCH 25

■ The huge, bright Winter Hexagon is still in view early after dark, filling the sky to the southwest and west. It's the biggest well-known asterism in the sky.

Start with brilliant Sirius in the southwest, the Hexagon's lower left corner. High above Sirius is Procyon. From there look higher upper right for Pollux and Castor (lined up nearly horizontal), lower right from Castor to Menkalinan and then bright Capella, lower left from there to Aldebaran, lower left to Rigel at the bottom of Orion, and back to Sirius.

The "Hexagon" is somewhat distended. But if you draw a line through its middle from Capella to Sirius, it's fairly symmetric with respect to that long axis.

TUESDAY, MARCH 26

■ Late this evening the Moon, two days day past full, shines about 4° lower left of 1st-magnitude Spica. Cover the Moon with your fingertip to hide its bright glare.

WEDNESDAY, MARCH 27

■ Castor and Pollux shine together nearly overhead in the south after dark. Pollux is slightly the brighter of these "twins."

Draw a line from Castor through Pollux, follow it farther out by a big 26° (about 2½ fist-widths at arm's length), and you're at the dim head of Hydra, the Sea Serpent. In a dark sky it's a subtle but distinctive star grouping, about the width of your thumb at arm's length. Binoculars show it easily through light pollution or moonlight.

Continue that line farther by a fist and a half and you hit 2nd-magnitude Alphard, Hydra's orange heart.

Another way to find the head of Hydra: It's almost midway from Procyon to Regulus.

THURSDAY, MARCH 28

■ A serious pre-sunrise challenge: On Friday morning the 29th, use large, well braced binoculars to look for Venus just above your east horizon about 20 or 15 minutes before sunrise. Look about a fist and a half to the right of where the Sun is about to come up.

Got Venus? Now the hard part. This morning, Saturn and Mars form an equal-spaced diagonal line with Venus, extending to its upper right in that order. The three planets are each 8½° apart. But both Mars and Saturn are about magnitude +1.2, only 1/100 as bright as Venus (before atmospheric extinction). Good luck. You'll need super-clear air.

FRIDAY, MARCH 29

■ Can you still see Mercury about two fists lower right of Jupiter in twilight? It's fading fast!

■ Perseus, with Algol on his stick-figure leg, is getting lower in the northwest as the season advances. So, this evening is one of your last good chances until next fall to catch Algol in eclipse. It should be at its minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 6:52 p.m. EDT; 9:52 p.m. PDT. Algol will take several additional hours to rebrighten. Comparison-star chart (with north up. Celestial north is always the direction in the sky toward Polaris).

SATURDAY, MARCH 30

■ Comet Pons-Brooks is low in the west right after dark. At a predicted 5th magnitude it should be fairly easy in binoculars and very interesting in a telescope. Look right after twilight ends. This evening it's passing only about ½° from 2nd-magnitude Alpha Arietis (Hamal). Look just to the star's right or lower right. The tail points up.

SUNDAY, MARCH 31

■ Right after dark, Sirius shines brilliantly in the south-southwest. Lower left of it, by about one fist, is the triangle of Adhara, Wezen, and Aludra, from right to left. They form Canis Major's hind foot, rear end, and tail, respectively. Or, alternatively, they're the lower end and handle of the Meat Cleaver.

Just left or upper left of the triangle, forming a 3rd- and 4th-magnitude arc that's a bit larger than the triangle, 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 1.5° upper right of the middle of the three, binoculars on a dark night will show the little 6th-magnitude open cluster M93. It's elongated northeast-southwest.

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This Week's Planet Roundup

Mercury awaits you low in evening twilight, but don't delay. About 45 to 60 minutes after sunset, look for it almost due west about two fists at arm's length below or lower right of bright Jupiter. Watch Mercury fade rapidly this week from a prominent magnitude –0.4 to a bashful +1.0 (a loss of nearly three quarters of its light) even as it remains at about the same height.

Venus, magnitude –3.8, is buried deep in the sunrise.

Mars, magnitude +1.2, rises above the southeast horizon after dawn begins but will probably remain hidden in the horizon murk and the brightening skyglow. It's about 16° upper right of Venus if you want to give a try.

Jupiter, magnitude –2.1 in Aries, is the bright "star" shining due west in twilight. It sinks lower after dark and sets around 10 or 11 p.m. It's becoming the only easy planet in the sky.

Saturn is probably invisible; it's a little to the right or upper right of Venus in the brightening dawn. Their separation widens from 2° to 9° this week. Being so low and only magnitude +1.1, Saturn will be even harder than Mars even with optical aid.

Uranus, magnitude 5.8 in Aries, hides 4° or 5° above Jupiter in the early evening sky. Right after darkness is complete, use the finder charts for Uranus in last November's Sky & Telescope, pages 48-49.

Neptune is lost in conjunction with the Sun.

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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 and graphics that also depend on longitude (mainly Moon positions) are for North America.

Eastern Daylight Time (EDT) is Universal Time minus 4 hours. UT is also known as UTC, GMT, or Z time.

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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 a more detailed 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 much more 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 all stars to magnitude 7.6.

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 mag 9.75). And read How to Use a Star Chart with a Telescope. It applies just as much to charts on your phone or tablet as to charts on paper.

You'll also want a good deep-sky guidebook. A beloved old classic is the three-volume Burnham's Celestial Handbook. An impressive more modern one is the big Night Sky Observer's Guide set (2+ volumes) by Kepple and Sanner.

Can computerized telescopes replace charts? Not for beginners I don't think, especially not on mounts and tripods that are less than top-quality mechanically. Unless, that is, you prefer spending your time getting finicky technology to work rather than learning the sky. 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."

If you do get a computerized scope, make sure the drives can be disengaged so you can swing it around and point it readily by hand if you want, rather than only slowly by the electric motors.

However, finding faint telescopic objects the old-fashioned way with charts isn't simple either. Learn the tricks at How to Use a Star Chart with a Telescope. 

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

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"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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