This Week’s Sky at a Glance, April 16 – 24

This has become a crackling month for novae! The newest is Nova Scorpii 2021. It popped up and peaked round magnitude 8.6 on April thirteenth, then rapidly dropped to 10.0 by the fifteenth. Will it rebound? See Bob King’s A Bouquet of Novae Brightens April Nights.

Nova Cassiopeiae 2021 (V1405 Cas) was, in the meantime, nonetheless holding regular at about magnitude 8.1 as of April fifteenth. It’s been about like that for 4 weeks now. See Bright Nova Erupts in Cassiopeia.

Comet ATLAS, at ninth magnitude, is crossing Hercules excessive within the early-morning sky, awaiting 6-inch and bigger telescopes. See Make the Most of Comet ATLAS.

At the tip of that article are information and charts for Nova Sagittarii 2021 No. 2 (V6595 Sgr), simply off the spout of the Sagittarius Teapot in good view earlier than the primary gentle of daybreak. In the final two weeks this one has pale steadily from magnitude 8.0 to 10.5.

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FRIDAY, APRIL 16

■ This night the waxing crescent Moon kinds a quadrilateral with Mars above it and Taurus’s horntip stars, Beta and fainter Zeta Tauri, to the edges as proven beneath.

Both Mars and the Moon go upward between the horntips of Taurus.

SATURDAY, APRIL 17

■ Now the Moon shines higher left of tiny Mars, as proven above.

■ Bright Arcturus ascends within the japanese sky throughout night whereas Capella, its shut match for brightness, descends within the northwest. They stand at precisely the identical altitude across the finish of twilight, relying in your location.

■ And at that point, the Sickle of Leo stands upright excessive within the south. Its backside star is Regulus, the brightest of Leo. Leo himself is strolling westward. The Sickle kinds his entrance leg, chest, mane, and a part of his head. Off to the left, a lengthy proper triangle kinds his hind finish and lengthy tail.

■ Spot brighter Procyon practically 4 fists to the decrease proper of Regulus. About midway alongside that line and simply a bit beneath, search for the dim head of Hydra, the Sea Serpent.

SUNDAY, APRIL 18

■ The Moon shines in central Gemini this night below Pollux and Castor, forming a lengthy, tall triangle with them. Farther left of the Moon is Procyon. Much farther proper of the Moon is Capella.

■ At this time of year, the 2 Dog Stars stand vertically aligned in late twilight. Look straight southwest. Brilliant Sirius in Canis Major is beneath, and Procyon in Canis Minor is excessive above. They’re roughly two fists aside.

■ This can be when, because the final of twilight fades away, the bowl of the dim Little Dipper extends straight to the precise of Polaris within the north.

■ And excessive above the end-stars of the Little Dipper’s bowl, you may discover the end-stars of the Big Dipper’s bowl. That pair is nearly twice as huge aside.

MONDAY, APRIL 19

■ First-quarter Moon (actual at 2:59 a.m. EDT). Look excellent of the Moon for Pollux and Castor practically lined up with it. Lower left of the Moon shines Procyon.

TUESDAY, APRIL 20

■ This night, use binoculars to select M44, the Beehive star cluster, about 4° or so beneath the Moon. That’s roughly two-thirds or three-quarters the width of a typical binocular’s discipline of view. This a lot moonlight is hardly very best for viewing a deep-sky object, however the Beehive stars should not tough in binocs, and the Moon does make a very useful reference level to begin from.

■ Arcturus shines brightly within the east these evenings. It’s the sharp finish of a lengthy, slender kite-shaped asterism fashioned by the brightest stars of Bootes, the Cowherd. The kite is at the moment mendacity on its aspect, extending to Arcturus’s left. The head of the kite, at the far left, is bent barely upward. The kite is 23° lengthy: about two fist-widths at arm’s size.

WEDNESDAY, APRIL 21

■ The Moon this night type an isosceles triangle with Regulus and Algieba (Gamma Leonis), the second-brightest star of Leo’s Sickle, as proven beneath. The actual top of the isosceles triangle will rely in your longitude, because the Moon strikes eastward by an considerable quantity every hour.

The scenes listed below are at all times plotted actual for an observer close to the center of North America, at latitude 40° N, longitude 90° W. If you are close to the East Coast the Moon will likely be simply a little to the precise of the place it is plotted beneath. On the West Coast the Moon will seem a little left of the place plotted.

By how a lot? Measure by the truth that the hole between the 2 Moons beneath is 24 hours of lunar movement.

The Moon passes between Regulus and Algieba (the orange star above Regulus) between the North American evenings of Wednesday and Thursday, April twenty first and twenty second. (The Moon is drawn about thrice its precise obvious measurement.)

■ In the early-morning hours of Thursday the Lyrid meteor bathe, normally weak however typically unpredictable, ought to at its most exercise. The gentle of the waxing gibbous Moon will intrude till the Moon units about an hour earlier than the primary glimmer of daybreak. That darkish hour is the very best window to plan for. See Robert Lunsford’s Viewing the Lyrids in 2021.

THURSDAY, APRIL 22

■ Now the Moon kinds a triangle with Regulus and Algieba on their left aspect slightly than their proper aspect, as proven above.

This new triangle is nearly completely equilateral across the time twilight ends within the Eastern and Central time zones.

FRIDAY, APRIL 23

The Arch of Spring. As evening descends, look excessive within the west for Pollux and Castor lined up virtually horizontally relying in your latitude. These two stars, the heads of the Gemini twins, type the highest of the large Arch of Spring. To their decrease left is Procyon, the left finish of the Arch. Farther to their decrease proper is the opposite finish, fashioned by Menkalinan (Beta Aurigae) after which good Capella.

This spring the Arch has an intruder: little Mars. Tonight you may discover Mars the identical distance decrease proper from the Castor-Pollux pair as it’s decrease left from Capella. The entire array sinks within the west by the night.

Modern skywatchers should not alone in seeing the Arch of Spring as one huge asterism. Extend it down previous Procyon so as to add Sirius, and you have the Hawai‘ian Canoe-Bailer of Makali‘i. Looks large enough to bail the ocean.

■ The Moon shines on the alternative aspect of the sky after darkish. Look higher left of the Moon by lower than fist at arm’s size for 2nd-magnitude Denebola, the tail star of Leo.

Nearly 4 fists left of the Moon shines brighter Arcturus, magnitude 0, the main gentle of Bootes.

SATURDAY, APRIL 24

■ This night Arcturus shines about three fists left of the Moon.

And look beneath the Moon by hardly greater than half that distance, and maybe a bit left, to seek out Spica, the main gentle of Virgo.

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This Week’s Planet Roundup

Mercury and Venus stay buried within the sundown, however not for lengthy. Next week they’re going to begin rising into low twilight view collectively.

Mars (magnitude +1.4, crossing from Taurus into Gemini) shines within the west after darkish. In a telescope Mars is a mere 5 arcseconds huge, simply a tiny shimmering blob.

Jupiter and Saturn (each in dim Capricornus) are low within the southeast simply earlier than and through early daybreak. Jupiter grabs the attention at magnitude –2.1. Saturn glows a thirteenth as vivid at magnitude +0.7. Catch Saturn a little greater than a fist at arm’s size to Jupiter’s proper or higher proper earlier than daybreak grows too vivid.

Jupiter’s Great Red Spot aspect, imaged on April third by Christopher Go from his tropical latitude of 10° north. The darkish dot just isn’t a moon’s shadow however darkish Callisto itself, caught in a uncommon equatorial transit throughout Jupiter.

South right here is up. The northern two thirds of the Equatorial Zone are pale orange tan slightly than white. Bordering the Equatorial Zone on the north is the darkish red fringe of the North Equatorial Belt.

Uranus and Neptune stay hidden low in night and morning twilight, respectively.


All descriptions that relate to your horizon — together with the phrases up, down, proper, and left — are written for the world’s mid-northern latitudes. Descriptions that additionally rely on longitude (primarily Moon positions) are for North America.

Eastern Daylight Time, EDT, is Universal Time minus 4 hours. Universal Time is also called UT, UTC, GMT, or Z time. To turn out to be extra knowledgeable about time techniques than 99% of the folks you may ever meet, see our compact article Time and the Amateur Astronomer.


Want to turn out to be a higher astronomer? Learn your way across the constellations. They’re the important thing to finding the whole lot fainter and deeper to hunt with binoculars or a telescope.

This is an outside nature interest. For an easy-to-use constellation information overlaying the entire night sky, use the large month-to-month map within the middle of every challenge of Sky & Telescope, the important journal of astronomy.

Once you get a telescope, to place it to good use you may want a detailed, large-scale sky atlas (set of charts). The primary normal is the Pocket Sky Atlas (in both the original or Jumbo Edition), which reveals stars to magnitude 7.6.

Pocket Sky Atlas cover, Jumbo edition
The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and a whole lot of telescopic galaxies, star clusters, and nebulae amongst them. Shown right here is the Jumbo Edition, which is in onerous covers and enlarged for simpler studying outdoor by red flashlight. Sample charts. (*16*).

Next up is the bigger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; practically thrice as many. The subsequent up, as soon as your way round, are the even bigger Interstellarum atlas (stars to magnitude 9.5) or Uranometria 2000.0 (stars to magnitude 9.75). And you’ll want to learn (*24*).

You’ll additionally need a good deep-sky guidebook, resembling Sky Atlas 2000.0 Companion by Strong and Sinnott, or the larger (and illustrated) Night Sky Observer’s Guide by Kepple and Sanner.

Can a computerized telescope substitute charts? Not for rookies, I do not assume, and never on mounts and tripods which are lower than top-quality mechanically, which means heavy and costly. And as Terence Dickinson and Alan Dyer say of 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 below the night sky along with your
earbuds in place, hearken to Kelly Beatty’s month-to-month
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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