The sky is damaged. For weeks now, Western and Canadian wildfires have launched a pall of smoke that blankets both countries. July eighth was the final smoke-free evening at my observing web site in northeastern Minnesota. Daytime skies are typically pale blue, with nights starved of stars. Often, the limiting magnitude is 2 or 3.
Because of fixed smoke I’ve needed to change up my observing from comets and deep-sky to brighter fare. Among the astronomical objects least affected by wildfires and haze are double stars. I hate to say it is a blessing, however the current thick skies have given me an excuse to revisit favourite duos I’ve ignored for too lengthy in pursuit of fainter quarry.
I share them with you right here. Some are apparent decisions, others off the overwhelmed path, however all are vibrant and beautiful. Though I used a 10-inch Dobsonian reflector for the observations, a 4-inch telescope needs to be greater than sufficient. I like utilizing the bottom potential magnification to separate doubles. Images are sharper and a wider subject of view makes a prettier backdrop. Except for the tighter couplets, 76× labored effectively.
Information for every pair contains star magnitudes, separation in arcseconds, and place angle (PA), the angle the secondary star makes to the first. In poor seeing or with shut pairs it is useful to know the precise location of the companion so you possibly can focus your consideration at that spot whereas ready for the environment to settle.
Finally, I’ve included info, a map, and pictures of a current vibrant supernova that is at the moment twelfth magnitude and visual in an 8-inch telescope. Have at it!
Selected Double Stars
- Eta (η) Cassiopeiae (magnitudes 3.5, 7.4; separation 13.4″ in PA 326°) — What colours! A tangerine main and purple-rose companion. One of the perfect unequal-magnitude pairs. Although spectrally not an awesome distance aside — F9 (main) + Ok7 (secondary) — the massive magnitude distinction between the stars and their shut proximity exaggerates the stars’ shade variations, a situation known as simultaneous color contrast. Real or imagined, you will need to expertise this.
- Xi (ξ) Boötis (4.8, 7.0; sep. 5.2″; PA 298°) — Another colourful pair although not fairly as putting as Eta Cassiopeiae. The elements are yellow and pale red (G7+Ok5), with a separation ranges from 2.5″ to 7″ throughout its 151.6-year mutual orbit.
- Mu (μ) Boötis (A=4.3, Ba=7.1 and Bb=7.6; sep. AB=109″, Ba-Bb=2.3″; PA of AB=172°, Ba-Bb=3°) — The vast pair is a binocular double, however by the telescope the companion is a phenomenal shut pair, making this a triple system.
- Σ 1962 Librae (6.4, 6.5; sep. 11.7″; PA 189°) — Neat, equal pair like cats’ eyes in your headlights.
- Beta (β) Scorpii (2.6, 4.5; sep. 13.4″; PA 20°) — Love at first sight. Beautiful, vibrant pair for low magnification. Some observers report yellow and blue, however they’re close to equals with B1+B2.
- Nu (ν) Scorpii (AB=4.4, 5.3; CD=6.6, 7.2; sep. AB=1.3″, CD=2.4″; PA of AB= 1°; CD= 56°) — Spectacular quadruple star, the Double Double of the southern summer time sky. A great check for a 4-inch.
- Mu (μ) Draconis (5.7, 5.7; sep. 2.7″; PA 358°) — Pleasingly shut (virtually cuddly), at medium and excessive magnifications. One of my favorites.
- Alpha (α) Herculis (3.5, 5.4; sep. 4.9″; PA 102°) — Radiant Rasalgethi is a red supergiant 475 occasions brighter than the Sun and makes for splendid distinction with its yellowish companion (M5+G5).
- Nu (ν) Draconis (4.9, 4.9; sep. 62.1″; PA 311°) — Beautifully matched pair that is good for binoculars!
- 95 Herculis (4.9, 5.2; sep. 6.4″; PA 257°) — Inexplicably colourful. Nineteenth-century astronomer Admiral Smythe known as them “apple-green” and “cherry-red.” I see red and white. Given that their spectral courses are A5+G8, the pair is a sterling instance of shade distinction. A ravishing, low-magnification duo.
- 70 Ophiuchi (4.2, 6.2; sep. 6.6″; PA 122°) — Two colourful Ok-type dwarfs with a separation that varies from 1.5″ to six.8″ over a interval of 88 years. They have been closest in 1989 and can be farthest aside in 2024. If you are younger put this star on the high of your checklist, as you might need the uncommon privilege of seeing the companion full a lot of its orbit round the principle star throughout your lifetime.
- Beta (β) Cygni 3.2, 4.7; sep. 34.6″; PA 54°) — Albireo by no means will get previous. I see hues of gold and pale blue (Ok3+B9.5), however I’ve heard all the things over the years: yellow, red, green, white . . . proving once more how subjective shade notion is. Spectacular subject!
- Gamma (γ) Delphini (4.4, 5.0; sep. 8.9″; PA 265°) — Bright, colourful pair within the nostril of the Dolphin comprising a cantaloupe main and lemon-yellow secondary (Ok1+F7). Shares the low-power subject with Σ 2725 (7.5, 8.2; sep. 6.2″; PA 12°), one other enticing pair 14′ to the southwest.
- Xi (ξ) Cephei (4.5, 6.4; sep. 8.1″; PA 274°) — My star occasion buddies are all the time stunned that Cepheus hides such a vibrant and fairly pair of stellar gems. They each seem white to me although some observers report them as bluish (A+F7).
Note: Double and a number of star knowledge are from the Washington Double Star Catalog and are present.
White dwarf goes growth!
On July 1st, the Zwicky Transient Facility (ZTF) found a supernova 7.8″ east and 1.0″ north of the middle of the intense galaxy NGC 7814 (magnitude 10.6, dimensions 5.5′ × 2.3′) in Pegasus. Named SN 2021rhu, it is since risen to round magnitude 12.2–12.5. Spectra point out it is a Type Ia explosion, the sort that happens in a detailed binary system when the companion star transfers hydrogen gas onto a white dwarf. The dwarf exceeds the Chandrasehkar Limit and burns catastrophically.
SN 2021rhu reaches 20° altitude round 11:30 p.m. native daylight time in late July. Use increased magnifications (150× to 300×) and look for a “star” near the galaxy’s vibrant nucleus. To keep abreast of developments with this and different supernovae make sure to go to Dave Bishop’s Latest Supernovae web page.