This Week’s Sky at a Glance, July 23 – 31

Nova Cas replace. Four months in the past Nova Cassiopeiae 2021 erupted to magnitude 7.7. It has stayed roughly that vivid ever since a “slow nova” however with a brightness spike to five.5 in early May and smaller bumps since. As of July twentieth it was 7.1. Charts and comparison stars.


■ Full Moon (actual at 10:37 p.m. EDT). The Moon is up within the east by late twilight. Look for Saturn about a fist at arm’s size to its left. Later after darkish, Jupiter rises farther to the Moon’s decrease left.

By daybreak on the twenty fourth, this group shifts to the southwest and twists clockwise in order that Saturn is above the Moon, as proven under.

Full Moon passing Saturn and Jupiter as seen at dawn, July 24-26, 2021.
The Moon passes Saturn, then Jupiter, when it is full and because it turns waning gibbous.


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

Venus, Regulus and Mars very low in the western twilight, July 24, 2021.
Venus marks the low west in twilight. Bring binoculars or a wide-field scope for one final strive at Regulus and even-dimmer Mars.

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

■ As summer season progresses, vivid Arcturus strikes down the western facet of the night sky. Its pale ginger-ale tint all the time helps determine it. Off to Arcturus’s proper within the northwest, the Big Dipper scoops to the best.


■ Look once more to Arcturus excessive within the west. In astronomy lore at present, Arcturus could also be greatest recognized for its cosmic historical past: It’s an orange big some 7 billion years previous, older than the solar system, racing by means of our a part of space on a trajectory that signifies it was born in one other galaxy: a dwarf galaxy that fell into the Milky Way and merged with it.

But within the astronomy books of our grandparents, Arcturus had a completely different declare to fame: It turned on the lights of the 1933 World’s Fair in Chicago celebrating “a century of progress.” Astronomers rigged the newly invented photocell to the attention finish of massive telescopes across the US and aimed them the place Arcturus would go at the right second on opening night time. The star’s mild crept onto the cells, the weak indicators have been amplified and despatched over telegraph wires to Chicago, and on blazed the large lights to the cheers of tens of 1000’s.

Why Arcturus? Astronomers of the time thought its was 40 light-years away (fashionable worth: 36.7 ±0.2). So the sunshine would have been in flight since Chicago’s earlier such occasion, the World’s Columbian Exhibition in 1893.

And earlier? Arcturus was the primary of the acquainted nighttime stars to be seen within the daytime with a telescope: by Jean-Baptiste Morin in 1635.


■ With the advance of summer season, the Sagittarius Teapot, within the south after darkish now, is tilting and pouring from its spout to the best. The Teapot will tilt farther and farther for the remainder of the summer season — or for a lot of the night time for those who keep out late.


Homing in on Hebe. The asteroid 6 Hebe is simply previous opposition, a magnitude 8.4 pinpoint north of the Sagittarius Teaspoon. A pair of 10×50 or bigger binoculars, used very rigorously below a darkish sky earlier than moonrise, could also be sufficient so that you can decide it out utilizing the finder chart within the July Sky & Telescope, web page 50. (The chart there exhibits Hebe’s place for 0:00 UT on the dates indicated, which falls on the night of the earlier date for North America.)


■ The lengthy, drawn-out Southern Delta Aquariid meteor bathe ought to peak someday round this date, although the sunshine of the waning gibbous Moon will intrude late tonight.

And talking of lengthy, drawn-out meteor showers, the Perseids have already begun. For now you may solely see the very occasional Perseid in the course of the course of your observing classes, however their numbers are step by step rising. The bathe is because of peak on the night time of August 11-12 below near-perfect moonless circumstances. See the August Sky & Telescope, web page 48.


Sunset problem. I’ve mentioned Regulus and Mars are disappearing for the season right down to Venus’s decrease left. Well, if you would like one final problem, Regulus and Mars this night are in conjunction, 0.6° aside.

Get Venus in your lowest-power, widest-field eyepiece as quickly after sundown as you’ll be able to. Then shift to observe 8° to Venus’s decrease proper to see whether or not you’ll be able to decide up Regulus and fainter Mars earlier than they get too low and set within the fading twilight, as proven right here:

Mars and Regulus are in conjunction. Good luck.

Fourth star for the Summer Triangle. The next-brightest star close to the Summer Triangle is Rasalhague, the pinnacle of Ophiuchus.

First determine the Triangle. Face east quickly after darkish and crane your neck excessive to identify vivid 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 best of Vega and three fists higher proper of Altair.

Admittedly, at 2nd magnitude it isn’t as vivid because the three Triangle stars. But embrace it and you have a big, flattened quadrilateral.


■ As summer season progresses, Arcturus strikes down the western facet of the night sky. Arcturus types the underside level of the Kite of Bootes. The Kite, fairly slim, extends higher proper from Arcturus by 23°, about two fists at arm’s size. The decrease proper facet of the kite is dented inward, as if some celestial intruder as soon as banged into it.


Saturn is at opposition tomorrow night time. Do you already discover that Saturn’s rings are distinctly brighter, in comparison with Saturn’s globe, than they normally are? This (*23*) is brought on by the strong ring particles backscattering sunlight to us when the Sun is nearly instantly behind us. The dusty surfaces of the Moon and Mars do that too, however Saturn’s clouds don’t. In the case of Saturn the impact is known as for Hugo von Seeliger, who studied it intimately and printed his findings in 1887.



This Week’s Planet Roundup

Mercury is out of sight deep within the glow of dawn.

Venus (magnitude –3.9) continues to shine low within the west throughout twilight. It units round twilight’s finish.

Mars is disappearing from sight deep within the sundown, decrease proper of Venus.

Saturn (magnitude +0.2, in Capricornus) and brighter Jupiter (magnitude –2.8, in Aquarius) shine within the east-southeast because the stars come out. Saturn is a lone, regular yellowish level. Jupiter shines brighter about two fists at arm’s size to Saturn’s decrease left. By late night they make a formidable duo larger within the southeast. They’re highest within the south, at their telescopic greatest, round 1 or 2 a.m. daylight saving time.

Saturn reaches opposition on August 1st, Jupiter on August nineteenth, in order that they’re already primarily as shut and massive as they’re going to get. See “Action at Jupiter” within the July Sky & Telescope, web page 50, and “Saturnian Challenges” beginning on web page 52. Also “Dog Days with the Gas Giants” within the August difficulty, web page 49.

Jupiter on July 12, 2021
Jupiter on July twelfth, imaged by Christopher Go. South is up. The South and North Equatorial Belts have principally diminished to skinny darkish strains. Red barges and spots proceed simply north of the NEB. Much of the Equatorial Zone continues pale yellow-tan. The Great Red Spot is on the opposite facet of Jupiter, however notice the row of white ovals within the south temperate space.

Uranus (magnitude 5.8, in Aries) is excessive within the east-southeast earlier than daybreak begins.

Neptune (magnitude 7.8, in Aquarius 23° east of Jupiter) is excessive within the south 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 also referred to as UT, UTC, GMT, or Z time. To change into extra skilled about time methods than 99% of the individuals you may ever meet, see our compact article Time and the Amateur Astronomer.

Want to change into 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 overlaying the entire night sky, use the massive month-to-month map within the heart of every difficulty 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 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 bunch of telescopic galaxies, star clusters, and nebulae amongst them. Shown right here is the Jumbo Edition, which is in laborious 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 3 times as many. The subsequent up, as soon as you realize your way round, are the even bigger Interstellarum atlas (stars to magnitude 9.5) or Uranometria 2000.0 (stars to magnitude 9.75). And make sure you learn (*31*).

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 exchange charts? Not for freshmen, 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, 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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