This Week’s Sky at a Glance, April 9 – 17 – Sky & Telescope

Nova Cassiopeiae 2021 (V1405 Cas) was still holding on at about magnitude 8.2 as of April 8th. See Bright Nova Erupts in Cassiopeia.

Comet ATLAS, currently 9th or 10th magnitude, is high in the early-morning sky moving from Aquila toward Hercules and awaiting 6-inch and larger telescopes. See Bob King’s Make the Most of Comet ATLAS.

And at the end of that article is info and a chart for the new Nova Sagittarii 2021 No. 2 just off the spout of the Sagittarius Teapot. It’s currently 8th magnitude and fairly well up in the south-southeast before the beginning of dawn.



■ As the stars begin to come out in late twilight, Arcturus, the bright Spring Star climbing up in the east, stands just as high as Sirius, the brighter Winter Star descending in the southwest. They’re both about 20° or 25° high 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 much higher in the northwest in early evening.


■ By late evening the Sickle of Leo stands nearly vertical high in the south. Its bottom star is Regulus, the brightest of Leo. Leo himself is walking 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.

Spot brighter Procyon nearly four fists to the right of Regulus and a bit lower. About halfway along that line and just a bit below, look for the dim head of Hydra, the Sea Serpent.


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

■ This is also 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 in the north.

High above the end-stars of the Little Dipper’s bowl, you’ll find the end-stars of the Big Dipper’s bowl. That pair is separated almost twice as widely.

■ New Moon (exact at 10:31 p.m. EDT).


■ Mars is crossing the line between the horntips of Taurus, Beta and Zeta Tauri, this evening and tomorrow evening.

Mars is only a trace fainter than Beta. But compare their colors: Beta is a bluish-white B7 star.


■ Vega, the bright “Summer Star,” rises in the northeast in mid-evening. Exactly where should you watch for it to come up? Spot the Big Dipper very high 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 will make its appearance.


■ Arcturus shines brightly in the east these evenings. It’s the pointy end of a long, narrow kite-shaped asterism formed by the brightest stars of Bootes, the Cowherd. The kite is currently lying on its side, extending 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.


■ The waxing crescent Moon shines near Aldebaran and the Pleiades this evening, as shown below.

This week both Mars and the Moon pass upward between the horntip stars of Taurus


■ The waxing crescent Moon this evening forms a quadrilateral with Mars above it and Beta and fainter Zeta Tauri to the sides, as shown above.


■ Now the Moon shines upper left of tiny Mars, as shown above.

■ As Arcturus ascends the eastern sky, Capella (its close match for brightness) is coming down 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.


This Week’s Planet Roundup

Mercury, Venus, Uranus, and Neptune all remain out of sight in the glare of the Sun.

Mars (magnitude +1.4, in Taurus) shines high in the west after dark. Watch it pass between Beta and Zeta Tauri, the horntips of Taurus, on April 12th and 13th. Mars is visibly fainter than orange Aldebaran down below it, not to mention brighter orange Betelgeuse to Mars’s left or lower left. In a telescope Mars is a mere 5 arcseconds wide: a tiny, shimmering blob.

Jupiter and Saturn (both in Capricornus) are low in the southeast just before and during early dawn. Saturn is slightly the higher of the two (depending on your latitude), but it’s much dimmer at magnitude +0.7. Jupiter shines at magnitude –2.1, about 13° to Saturn’s lower left.

Jupiter’s Great Red Spot side, imaged on April 3rd by Christopher’s Go from his tropical latitude of 10° north. The dark dot is not a moon’s shadow but dark Callisto itself, caught in a rare equatorial transit across Jupiter. South here is up. The northern two thirds of the Equatorial Zone are pale orange tan rather than white. It’s bordered on the north by the dark red edge of the North Equatorial Belt.

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 Daylight Time, EDT, is Universal Time minus 4 hours. Universal Time is also known as UT, UTC, GMT, or Z time. To become more expert about time systems than 99% of the people you’ll ever meet, see our compact article 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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