This Week's Sky at a Glance, April 12 – 21

Periodic Comet Pons-Brooks is still at its predicted peak brightness, about magnitude 4.5, as it gets lower in the west right at the end of twilight. Binoculars can reveal it as a little gray fuzzball among the stars even through a typical suburban sky. Brightness outbursts are possible; the comet has had two big ones in the last year (brightening by 5 and 3 magnitudes!) so check every clear evening.

This week the comet passes about 3° below Jupiter and then moves farther to the left. It's dim enough that you'll have to know just where to look, especially with the moonlight now brightening night by night. Use the finder chart with the article in the March Sky & Telescope, page 48, and/or this interactive chart (set your date there, and note the field sizes in the captions. 10° is nearly twice the width of a typical binocular's field of view. The direction down on the charts is probably not down in your view).

On March 31st I spotted the comet near Alpha Arietis with 10x50 binocs through a mediocre suburban sky, just at the end of twilight. It was a little gray fuzzball, elongated upward. I didn't 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 5 weeks or so Betelgeuse has held at about mag +0.7. That amounts to hardly more than its usual slow wobbles. Will it resume fading? Or rebrighten? Keep watch using Aldebaran and Procyon as your comparison stars.

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FRIDAY, APRIL 12

■ Four days after the Moon eclipsed the Sun, it is a thickening crescent in the evening sky. Tonight it's just below Beta Tauri (El Nath), which at magnitude +1.6 just misses being a 1st-magnitude star.

Far to their right or upper right is brighter Capella. A little farther to their left or lower left is Betelgeuse.

SATURDAY, APRIL 13

■ This is the time of year when, as the last of twilight fades away, the bowl of the dim Little Dipper extends straight to the right of Polaris. High above the two end-stars of the Little Dipper's bowl, you'll find the two end-stars of the Big Dipper's bowl.

■ Arcturus shines brightly in the east these evenings. The Big Dipper, high in the northeast, points its curving handle to the lower-right down toward it.

Arcturus forms the pointy end of a long, narrow kite asterism formed by the brightest stars of Boötes, the Cowherd. The kite is currently lying on its side to Arcturus's left. The head of the kite, at the far left, is bent slightly upward. The kite is 23° long, about two fist-widths at arm's length.

SUNDAY, APRIL 14

■ Now the Moon, less than a day from first quarter, hangs under Pollux and Castor in upright-standing Gemini.

MONDAY, APRIL 15

■ First-quarter Moon (exact at 3:13 p.m. EDT). The Moon shines high at nightfall left of Pollux and Castor. Far below the Moon is Procyon. Farther below Procyon shines Sirius.

■ To the right of Procyon and Sirius is Betelgeuse, Orion's upper shoulder. The three form the equilateral Winter Triangle. Orion is walking down into the southwest in his spring orientation: tilting to the right with his belt horizontal.

The belt points left back toward Sirius and right toward Aldebaran and, farther on, the Pleiades.

TUESDAY, APRIL 16

■ Vega, the bright "Summer Star," rises in the northeast these evenings. How early or late depends on your latitude and also on your longitude within your time zone.

Exactly where should you watch for Vega 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 17

■ Right after dark the waxing gibbous Moon shines high in the south, with the Sickle of Leo standing vertical just to its left . The top of the Sickle almost curls around the Moon.

The Sickle's bottom star is Regulus, Leo's the brightest. Leo himself is walking horizontally westward. The Sickle forms his front leg, chest, mane, and part of his head. Off to the left, a long right triangle forms his hind end and long tail.

THURSDAY, APRIL 18

■ The Moon is now deeper in Leo, forming an isosceles triangle (two equal sides) with Regulus to its right and Algieba (Gamma Leonis) farther above them.

FRIDAY, APRIL 19

■ Bright Arcturus climbs high in the east these evenings. Equally bright Capella descends high in the northwest. They stand at exactly the same height above your horizon at some moment between about 9 and 10 p.m. daylight-saving time, depending mostly on how far east or west you live in your time zone.

How accurately can you time this event for your location? Like everything constellation-related, it happens 4 minutes earlier each night.

SATURDAY, APRIL 20

■ While Arcturus, pale yellow-orange, is the brightest star high in the east these evenings, lesser Spica, pale blue-white, shines lower right of it — by about three fists at arm's length.

To the right of Spica by half that distance, look for the distinctive four-star constellation of Corvus, the springtime Crow.

SUNDAY, APRIL 21

■ As night descends, look high in the west for Pollux and Castor lined up almost horizontally (depending on your latitude). These two stars, the heads of the Gemini twins, form the top of the enormous Arch of Spring. To their lower left is Procyon, the left end of the Arch. Farther to their lower right is the other end, formed by Menkalinan (Beta Aurigae) and then brilliant Capella. The whole thing sinks in the west through the evening.

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This Week's Planet Roundup

Mercury, Venus, and Neptune are hidden in the glare of the Sun.

Mars and Saturn, both about magnitude +1.2, rise soon after dawn begins. Look for them just above the east-southeast horizon about 45 minutes before sunrise. Mars is the redder one, on the left. They widen from 2½° apart on the morning of April 13th to 6½° on the 20th.

Jupiter, magnitude –2.1 in Aries, is the bright "star" low in the west-southwest in twilight. It sinks lower after dark and sets less than an hour after full dark.

Uranus, magnitude 5.8, hides a mere 1½° above Jupiter early in the week. Low altitude and lingering twilight make it a hard catch. It's in conjunction with Jupiter, ½° to Jupiter's upper right, on the 20th when they're even lower. Immediately after dark, as soon as you're done with Comet Pons-Brooks lower still, use binoculars or a good finderscope to identify Uranus using the finder charts in last November's Sky & Telescope, pages 48-49 (which do not show Jupiter).

In a telescope, the dim planet's giveaway is that it's slightly nonstellar at fairly high power (it's 3.4 arcseconds wide). But the atmospheric seeing at such a low altitude will be awful; stars may appear nearly that big.

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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 when you want to, rather than only slowly by the electric motors (which eat batteries).

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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