This Week's Sky at a Glance, March 29 – April 7

Periodic Comet Pons-Brooks has brightened on schedule and is now 5th magnitude, near its expected peak of 4.5. That puts it in range of binoculars even in a not-so-good suburban sky, and it is detectable naked-eye in a truly black sky. Brightness outbursts are possible; the comet has had two big ones in the last year (of 5 and 3 magnitudes!), so check it every clear evening.

Pons-Brooks is low in the west-northwest right after the end of twilight. It's to the lower right of Jupiter and heading toward it, crossing Aries. But you'll have to know where to look! Use the finder chart with the article in the March Sky & Telescope, page 48, or this interactive chart online. For mid-northern observers, Pons- Brooks should be at its best this week and into next. Its tail points upward.

On Saturday evening March 31st I easily spotted it near Alpha Arietis with 10x50 binocs through a mediocre suburban sky, just at the end of twilight. It was a little fuzzball, elongated upward. I didn't even need averted vision.

Betelgeuse has stopped 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 its one in winter 2000. But for the last month 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 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. Outside at night, turn the chart around to match.

SATURDAY, MARCH 30

■ Comet Pons-Brooks is low in the west right after dark. At a predicted 5th magnitude it should not be hard in binoculars if you get aimed right, 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 that 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 just 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 can show the little 6th-magnitude open cluster M93. It's elongated northeast-southwest.

MONDAY, APRIL 1

■ The huge, bright Winter Hexagon is still in view early after dark, filling the sky to the southwest and west. 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 (its two brightest stars), it's pretty symmetric with respect to that long axis.

■ Last-quarter Moon tonight (exactly so at 11:15 p.m. EDT). The Moon doesn't rise until around 3 a.m. daylight-saving time Tuesday morning, depending on your location. Once it's fairly well up in the southeast just before dawn begins, you can see that it's right near the handle of the Sagittarius Teapot, which sits horizontally at that time.

TUESDAY, APRIL 2

■ This is the time of year when the dim Little Dipper juts to the right from Polaris (the Little Dipper's handle-end) during late evening. With the Moon gone from the evening sky, the subtle Little Dipper stands out as well as it ever does.

The much brighter Big Dipper curls over high above it, "dumping water" into it. They do the reverse water dump in the fall.

■ Vega, the bright "Summer Star," rises in the northeast these evenings. How early or late depends on your latitude and on your longitude within your time zone. Exactly where should you watch for it to come up? Spot the Big Dipper almost overhead in the northeast. Look at Mizar at the bend of its handle. If you can see Mizar's tiny, close companion Alcor (binoculars show it easily), follow a line from Mizar through Alcor all the way down to the horizon. That's where Vega makes its appearance.

WEDNESDAY, APRIL 3

■ Castor and Pollux shine together west of the zenith after dark. Pollux is slightly the brighter of these "twins."

Draw a line from Castor through Pollux, follow it farther out by 26° (about 2½ fist-widths at arm's length), and you're at the dim head of Hydra, the Sea Serpent, in the south. 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.

Continue that line farther on by 1½ fists and you hit Alphard, Hydra's orange, 2nd-magnitude heart.

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

THURSDAY, APRIL 4

■ The bright star very high in the west-northwest during and after dusk is Capella. Its pale-yellow color matches that of the Sun, meaning they're both about the same temperature. But otherwise Capella is very different. It consists of two yellow giant stars orbiting each other every 104 days.

Moreover, for telescope users, it's accompanied by a distant, tight pair of red dwarfs: Capella H and L, magnitudes 10 and 13. Article and finder charts.

FRIDAY, APRIL 5

■ Shortly after nightfall around this time of year, Arcturus, the bright Spring Star climbing in the east, stands just as high as Sirius, the brighter Winter Star descending in the southwest (for skywatchers at mid-northern latitudes).

These are the two brightest stars in the sky at the time. But Capella is a very close runner-up to Arcturus! Spot it high in the northwest.

SATURDAY, APRIL 6

■ More Sirius doings: The two Dog Stars stand vertically aligned around the end of twilight. Sirius in Canis Major is the bottom one, and Procyon in Canis Minor is high above it.

When will they appear exactly vertical for your location and date? Hint: Like everything else among the fixed stars, this happens 4 minutes earlier each day.

SUNDAY, APRIL 7

■ High above the Big Dipper late these evenings, nearly crossing the zenith, are three pairs of dim naked-eye stars, all 3rd or 4th magnitude, marking the Great Bear's feet. They're also known as the Three Springs (or Leaps) of the Gazelle, from early Arab lore. They form an east-west line that lies roughly midway between the Bowl of the Big Dipper and the Sickle of Leo. The line is 30° (three fists) long. See the evening constellation chart in the center of the April Sky & Telescope.

According to the ancient Arabian story, the gazelle was drinking at a pond — the big, dim Coma Berenices star cluster — and bounded away when startled by a flick of Leo's nearby tail, Denebola. Leo, however, seems quite unaware of all this, facing the other way.

Another version sees Coma Berenices as Leo's extended tailtip and the pond as formed by stars in Ursa Major. For more of the legend see Steve O'Meara "Springs of the Gazelle" in the April Sky & Telescope, page 45.

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This Week's Planet Roundup

Mercury is fast fading away low in the western evening twilight. As the week begins, look for it about 45 minutes after sunset about two fists at arm's length lower right of bright Jupiter, as shown near the top of this page. Mercury fades rapidly from magnitude +1.0 on March 29th to invisibility just a few days later.

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

Mars, magnitude +1.2 in Aquarius, rises after dawn begins. Try for it just above the east-southeast horizon about 45 minutes before sunrise. Binoculars help.

Jupiter, magnitude –2.1 in Aries, is the bright "star" shining due west in twilight, not very high. It sinks lower after dark and sets around 10 p.m. It's the only easy planet in the entire sky now.

Saturn (magnitude +1.1) is still probably invisible in bright dawn. If you catch Mars in binoculars, however, take a look for Saturn to its lower left, especially later in the week. Their separation narrows from 8° on the morning of March 30th to 2½° on April 6th.

Uranus, magnitude 5.8 in Aries, hides about 4° above Jupiter in the early evening sky. Immediately after dark, after you're done with Comet Pons-Brooks nearby, use your binoculars to find Uranus with the finder charts in last November's Sky & Telescope, pages 48-49 (which do not show Jupiter).

Neptune is hidden deep in the sunrise.

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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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