This Week’s Sky at a Glance, August 13 – 21

RS Ophiuchi erupts. For the primary time since 2006, on August eighth the well-known recurrent nova RS Ophiuchi lept from its regular magnitude 11.2 to 4.8, dim naked-eye magnitude. In the primary week after its previous outbursts RS Oph has light easily by about two magnitudes, then it declines extra slowly right down to regular. See Bob King’s Recurrent Nova RS Ophiuchi Just Blew its Top! with finder charts and comparability stars. Ophiuchus is ideally positioned excessive within the night sky.

Nova Cas fades. Nova Cassiopeiae 2021 has bounced round in brightness ever because it erupted from fifteenth magnitude to 7.7 in March. Among its bumps had been brightenings to magnitude 5.5 in early May and 6.0 round July twenty seventh. As of August twelfth it was right down to about 8.5. Charts and comparison stars. Cas too is excellently positioned within the night sky.


■ A twilight problem: as twilight fades, study Venus with binoculars or a small telescope. You could discover a tiny spark barely 0.1° from it (beneath it as seen from mid- North America). That’s Beta Virginis. At visible magnitude 3.6, Beta Vir is 1,000 instances fainter than Venus.

■ Much simpler: Look for 1st-magnitude Spica decrease proper of the Moon, by a little lower than a fist at arm’s size. Much increased to their higher proper shines brighter Arcturus.


■ The brightest star excessive within the southeast these evenings is Altair, with little orange Tarazed above it by a finger-width at arm’s size.


■ First-quarter Moon (actual at 11:20 a.m. EDT). This night the Moon shines close to the top of Scorpius. Look left of the Moon for the roughly vertical row of Beta, Delta, and fainter Pi Scorpii, between the Moon and Antares. Delta’s correct identify, Dschubba, is from the Arabic for “Forehead” of the scorpion.

Delta is the brightest of the three. It’s an irregular variable star: a fast-rotating blue subgiant throwing off luminous gas from its equator. It has a smaller orbiting companion that appears to set off extra such exercise at 10.5-year intervals. Long presumed to be secure, Delta unexpectedly doubled in brightness in the summertime of 2000 and has remained practically that vibrant, with fluctuations, for most of the years since.

Astronomers are ready to see whether or not it can show one other flareup quickly, when the companion makes its third go by the first star because the instability began in 2000.


■ Now the Moon shines higher left of Antares, as proven beneath (for North America).

Right after first quarter the Moon shines close to Antares, then excessive over the Cat’s Eyes.

■ Regarding the Moon in your scope, have you ever ever made a research of lunar craters’ central peaks? Explore them and the physics behind them with Chuck Wood’s “Hills in the Middle” within the August Sky & Telescope, web page 52.


■ After dusk, look far beneath the Moon for the Cat’s Eyes within the tail of Scorpius (as proven above for mid-twilight). These are Lambda and fainter Upsilon Scorpii, 0.6° aside and canted at an angle; the cat is tilting its head to the appropriate. And the cat has a bleary eye; Upsilon is fainter than Lambda (they’re magnitudes 2.6 and 1.6). Both are blue-white giants, 500 and 700 gentle years away, respectively. Yes, the fainter one is the nearer one.


■ Way, way, way down low within the vibrant afterglow of sundown, Mercury and Mars are in conjunction solely 0.1° aside (for North America). About 15 or 20 minutes after sundown, use binoculars or a small telescope to attempt to decide up Mercury a few levels above the horizon. It’s a hint to the appropriate of due west, far decrease proper of Venus. You’ve bought a pretty good probability; Mercury is at present magnitude –0.5. Mars is one other story; at magnitude +1.8 it is solely an eighth as vibrant. Good luck with that. . . .

■ After darkish, look above the waxing gibbous Moon for 2nd-magnitude Sigma Sagittarii (Nunki). It’s the brightest star within the deal with of the Sagittarius Teapot.

The Moon’s darkish limb occults Nunki for Florida and different components of the southernmost US, Mexico, Central America, and the Caribbean; map and timetables.


■ The Moon types a nice, curving arc with Saturn and brighter Jupiter, that are to its left.

■ Jupiter is at opposition, reverse the Sun as seen from Earth. Among different issues, this implies the tiny black shadows of Jupiter’s moons cross the face of the planet very near the moons themselves. Both the shadows and the moons enter and exit Jupiter’s edges simply a couple of minutes from one another. See timetables for all these occasions (in addition to for when Jupiter’s Great Red Spot transits the planet’s central meridian) within the August Sky & Telescope, pages 51-52.


■ The vibrant Moon shines below Saturn this night, and Jupiter shines to their left, as proven beneath.

Moon under Saturn, then Jupiter, Aug 20 and 21, 2021
As the Moon turns full it hangs below Saturn, then Jupiter which, not coincidentally, are at opposition this month. This scene is in twilight; within the subsequent few hours watch the entire sample climb and switch clockwise.

■ The two brightest stars of summer time are Vega, now overhead shortly after dusk, and Arcturus, shining within the west. Draw a line down from Vega to Arcturus. A 3rd of the way down, the road crosses the dim Keystone of Hercules. Two thirds of the way down the road crosses the dim semicircle of Corona Borealis with its one modestly vibrant star, Alphecca or Gemma.

Vega and the Keystone’s star closest to it type an equilateral triangle with Eltanin to their north: the nostril of Draco the Dragon. Eltanin is the brightest star of Draco’s quadrilateral head. He’s eyeing Vega.


■ Now the Moon shines below Jupiter, with Saturn to their proper.

■ As summer time progresses and Arcturus strikes down the western sky, the kite determine of Bootes that sprouts up from Arcturus tilts to the appropriate (relying in your latitude). The kite is slender, barely bent with its high leaning proper, and 23° lengthy: about two fists at arm’s size. Arcturus is its backside level the place the stubby tail is tied on.

The Big Dipper now slants at about the identical peak within the northwest, to the Kite’s proper.


This Week’s Planet Roundup

Mercury and Mars are very deep within the sundown. You may have a probability for Mercury. About 15 or 20 minutes after sundown, search for it with binoculars or a wide-field scope simply above your west horizon about 20° (two fists at arm’s size) decrease proper of Venus. Mercury dims from magnitude –0.8 to –0.4 this week, so earlier within the week is healthier.

Much-fainter Mars is in Mercury’s neighborhood, passing it by a mere 0.1° at their conjunction on the 18th (as seen in twilight for the Americas). But since Mars is simply magnitude 1.8, you in all probability have zero probability. Prove me flawed?

Venus, sensible at magnitude –3.9, shines pure white within the west throughout twilight. It units round twilight’s finish.

Jupiter and Saturn shine within the southeast in late twilight and after darkish. They’re magnitudes –2.9 and +0.2, respectively, in or very close to Capricornus.

Jupiter begins the evening lowest. Saturn glows 19° (about two fists) to Jupiter’s higher proper. The pair ranges out round 11 or midnight daylight-saving time. By then they’re about at their highest within the south, at their telescopic greatest.

Saturn reached opposition on August 1st. Jupiter does so on August nineteenth. So this month they’re at their closest, greatest, and brightest of the year. See “Saturnian Challenges” beginning on web page 52 of the July Sky & Telescope, additionally “Action at Jupiter” within the August issue, web page 50, and “Dog Days with the Gas Giants” on web page 40 of August.

Jupiter’s Great Red Spot aspect, imaged on August seventh by Christopher Go with a 14-inch Schmidt-Cassegrain scope. This is a stacked-video picture, de-rotated throughout frames and with colours and distinction boosted. South is up. Note the high quality element within the Great Red Spot! The South and North Equatorial Belts have principally diminished to slender dark-reddish traces. Small, dark-red spots proceed simply north of the NEB. Much of the Equatorial Zone continues pale yellow-tan.
Saturn on July 25, 2021
Saturn on July 25. North is up. This beautiful stacked-video picture exhibits element within the broad A Ring, in addition to the skinny Encke Gap simply contained in the outer fringe of the outer B Ring. Saturn’s Equatorial Zone is vibrant as traditional, and the darker North Equatorial Belt is kind of distinct. Agapios Elia of Nicosia, Cyprus, took video throughout 45 minutes on July twenty fifth utilizing a 9.25-inch Schmidt-Cassegrain scope. He stacked giant numbers of the perfect frames after de-rotating the globe throughout processing.

Uranus (magnitude 5.7, in Aries) and Neptune (magnitude 7.8, at the Aquarius-Pisces border) are excessive within the southeast to south within the pre-dawn hours.

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 turn out to be extra knowledgeable about time methods than 99% of the folks you will 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 every little thing fainter and deeper to hunt with binoculars or a telescope.

This is an out of doors nature passion. For an easy-to-use constellation information protecting the entire night sky, use the massive month-to-month map within the heart of every situation 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 (*21*)), 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 onerous 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; practically 3 times 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 should definitely learn how to use sky charts with a telescope.

You’ll additionally need a good deep-sky guidebook, akin 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 substitute charts? Not for novices, 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, “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, take heed to Kelly Beatty’s month-to-month
podcast tour of the heavens above. It’s free.

            — Carl Sagan, 1996

“Facts are stubborn things.”
            — John Adams, 1770

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