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

Nova Cas replace. It’s been 4 months since Nova Cassiopeiae 2021 erupted to magnitude 7.7. It has stayed roughly that brilliant ever since, making it a “slow nova,” however with a brightness spike to five.5 in early May and smaller bumps since. As of July fifteenth it was about 8.0. Charts and comparison stars.


■ Venus continues to shine low within the western twilight this week. Tiny, distant Mars, a mere 1/200 as brilliant, is sliding away to Venus’s decrease proper as proven under. Meanwhile, twinkly Regulus, a half magnitude brighter than Mars, is quickly transferring in on Venus from the higher left. Regulus will move 1° from Venus on Wednesday the twenty first.

Now Mars strikes away to the decrease proper from Venus, whereas brighter Regulus houses in on Venus from the higher left. Regulus will move 1° from Venus on the night of the twenty first.

■ First-quarter Moon this night and tomorrow night (the Moon is precisely first quarter at 6:11 a.m. on July seventeenth EDT). Tonight, spot Spica about 6° to the Moon’s decrease left.


■ Now the eastward-marching Moon, nonetheless basically first-quarter, shines with Spica to its decrease proper.

■ Orange Antares and the remainder of starry Scorpius are highest within the south simply after darkish, with Antares about three fists left of the Moon. Don’t let the moonlight cease you. Scorpius is brilliant, and it is wealthy in double stars for binoculars and telescopes brilliant sufficient to shine proper by way of. Here’s a rundown:

The head of Scorpius is the vertical row of three stars to the suitable of Antares. The prime of the row is Beta Scorpii, a nice telescopic binary: separation 13 arcseconds, magnitudes 2.8 and 5.0.

Just 1° decrease left of it’s the very broad naked-eye pair Omega1 and Omega2 Scorpii, diagonal from higher proper to decrease left. They’re 4th magnitude and ¼° aside. Binoculars present their slight coloration distinction; they’re spectral varieties B9 and G2.

Upper left of Beta by 1.6° is Nu Scorpii, separation 41 arcseconds, magnitudes 3.8 and 6.5. In truth that is a telescopic triple. High energy in good seeing reveals Nu’s brighter element itself to be a shut double, separation 2 arcseconds, magnitudes 4.0 and 5.3, aligned nearly north-south.

■ And the tail of Scorpius, the constellation’s different finish, is about two fists decrease left of Antares. Look for the 2 stars particularly shut collectively within the tail. These are Lambda and fainter Upsilon Scorpii, the Cat’s Eyes. They’re canted at an angle; the cat is tilting his head a little to the suitable and winking (Lambda is brighter than Upsilon; they’re magnitudes 1.6 and a couple of.6). They’re 0.6° aside.

A line by way of the Cat’s Eyes factors to the suitable or decrease proper by almost a fist towards Mu Scorpii, a a lot tighter pair often called the Little Cat’s Eyes. These are oriented nearly precisely the identical way as Lambda and Upsilon, however they’re solely 0.1° aside, and fainter: magnitudes 3.0 and three.5.


■ Cassiopeia is now effectively previous its bottoming-out for the year. Look for its tilted W sample slowly transferring up within the north-northeast. The farther north you reside, the upper it is going to be.


■ Now the waxing gibbous Moon is horning proper in on the top of Scorpius, passing between Beta and Delta Scorpii in night for jap and central North America. Antares is about 7° to the Moon’s decrease left.


■ Now the Moon shines about a fist above the Cat’s Eyes and the Little Cat’s Eyes. See July 17 above.


■ Low within the western twilight, Venus is now along side Regulus. The star glimmers just one/140 as brilliant as Venus, about 1.1° decrease left of it as proven under.

Venus and Regulus are in conjunction this night, 1° aside. With binoculars, can you continue to decide up Mars 5° to their decrease proper? The visibility of faint objects in twilight is exaggerated right here.


Fourth star of the Summer Triangle. The next-brightest star close to the Summer Triangle, if you wish to flip it into a quadrilateral, is Rasalhague, the top of Ophiuchus.

First establish the Triangle. Face east quickly after darkish and crane your neck excessive to identify brilliant Vega. Look two fists decrease left of it for Deneb. Three or 4 fists decrease proper of Vega is Altair.

Next, Rasalhague. As you continue to face east, it is three fists to the suitable of Vega and three fists higher proper of Altair.

Admittedly, at 2nd magnitude it isn’t as brilliant because the three Triangle stars. But embody it and you have got a large, flattened quadrilateral.


■ The Moon, simply after full, is up shining brightly within the east by late twilight. Look for Saturn about a fist at arm’s size to the Moon’s left. By daybreak on the twenty fourth they shift to the southwest and twist round in order that Saturn is above the Moon, as proven under.

The waning gibbous Moon passes Saturn, then Jupiter.


■ Now each Regulus and Mars are effectively right down to Venus’s decrease proper, by 4° and seven° respectively as proven under . Bye-bye!

Bring binoculars or a wide-field scope for a final attempt at the 2 departing fainties.

■ And within the east after darkish, Saturn shines higher proper of the Moon and Jupiter shines farther to the Moon’s left. Again, by daybreak this scene of motion shifts to the southwest with the sample reoriented. See the graphic for daybreak on July 24–26 above.

■ As summer season progresses, brilliant Arcturus strikes down the western facet of the night sky. Its pale ginger-ale tint all the time helps establish it.

Off to Arcturus’s proper within the northwest, the Big Dipper scoops to the suitable.



This Week’s Planet Roundup

Mercury this week sinks even decrease down towards the east-northeast horizon in brilliant daybreak. But it does continues to brighten: from magnitude –0.8 to –1.5.

Venus (magnitude –3.9) continues to shine low within the west throughout twilight. Lower left of it’s tiny Mars, 200 occasions fainter at magnitude +1.8. Mars will get decrease daily. Both planets set earlier than twilight ends.

Upper left of Venus you will discover Regulus early within the week, transferring nearer to Venus day-to-day. It’s brighter than Mars by a half magnitude, not even counting their totally different quantities of atmospheric extinction. It passes 1° from Venus on the twenty first.

Saturn (magnitude +0.2, in Capricornus) and brighter Jupiter (magnitude –2.8, in Aquarius) rise within the east-southeast in twilight, Jupiter an hour after Saturn. By late night they make a powerful duo within the southeast. Jupiter will seize your eye first. Find Saturn 20° to its higher proper.

They’re highest within the south, at their telescopic finest, round 2 a.m. daylight saving time. See “Action at Jupiter” within the July Sky & Telescope, web page 50, and “Saturnian Challenges” beginning on web page 52. They’ll attain opposition subsequent month, in order that they’re already about as shut and massive as they’re going to get.

Uranus (magnitude 5.8, in Aries) is effectively positioned within the east earlier than daybreak begins.

Neptune (magnitude 7.8, in Aquarius 22° east of Jupiter) is larger within the south-southeast earlier than daybreak begins.

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 upon longitude (primarily Moon positions) are for North America.

Eastern Daylight Time, EDT, is Universal Time minus 4 hours. Universal Time is often known as UT, UTC, GMT, or Z time. To grow to be extra knowledgeable about time techniques than 99% of the individuals you will ever meet, see our compact article Time and the Amateur Astronomer.

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

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

Once you get a telescope, to place it to good use you will want a detailed, large-scale sky atlas (set of charts). The fundamental customary is the Pocket Sky Atlas (in both the original or Jumbo Edition), which exhibits 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 exhausting covers and enlarged for simpler studying open air by red flashlight. Sample charts. More about the current editions.

Next up is the bigger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; almost thrice as many. The subsequent up, as soon as you already know 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 how to use sky charts with a telescope.

You’ll additionally need a good deep-sky guidebook, equivalent to 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 change charts? Not for newcomers, I do not suppose, and never on mounts and tripods which can be lower than top-quality mechanically, that means heavy and costly. And as Terence Dickinson and Alan Dyer say of their Backyard Astronomer’s Guide, (*16*)

Audio sky tour. Out underneath the night sky together with your
earbuds in place, take heed 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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