For your enjoyment, here's a diverse selection of double stars in Draco for small and medium telescopes.

Cuddly coils
Who needs a TV dragon when you can spend an evening with Draco?
Urania's Mirror / Public Domain

One thing about double stars. They're not compromised by a bright moon. No matter the lunar phase, these duos are ready to charm. With TV watchers focused on the final installment of the TV series Game of Thrones in the coming weeks, it seemed only fitting to sample the gem-like treasures of the sky dragon. Never mind Rhaegal, Drogon, and Viserion, give me ever-reliable Draco.

Unlike the televised dragons, Draco's been recognized since at least the 2nd century, when Ptolemy included it in his list of the 48 constellations. According to myth, the becoiled beast guarded the golden apples of the Hesperides. Hercules killed the dragon and stole the apples in the 11th of his 12 labors. Despite Draco's fatal end, the two remain constellation neighbors to this day, unlike Orion and the distant scorpion.

Draco winds and twists its way between the Dippers and across the northern sky nearly to Vega. Despite having no star brighter than magnitude 2.2 (Etamin), the constellation has always been easy to pick out because its many stars naturally form a snake-like figure. When I'm out with the public, one quick swish with the green laser light and most people have no trouble seeing the shape. The tail starts just off the Big Dipper's Pointer Stars and ends with the dragon's head — a quadrilateral asterism dubbed the Lozenge — 14° from Vega.

I used to think that the word draconian, an adjective meaning harsh or severe, had something to do with the evil mood of dragons. But it refers instead to Draco (a.k.a. Drakon), a 7th-century-BC Greek lawmaker who replaced the then-current oral code of law with one written on wooden tablets. Draco preferred harsh, unforgiving punishments. Steal an apple or cabbage and the penalty was death.

Doubling up in Draco
Featured double stars are circled on this map. Click for a large version and print out for use at the telescope.
Stellarium with additions by the author

I promise no severe penalties for failing to split each of the double stars we're about to examine. In selecting a sweet set of pairs, I tried to pick those that closely followed the dragon's coils for a visceral experience of twisting and turning while working your way from one to the next. Since that would have eliminated several choice gems, I expanded the bounds a bit to include several additional pairs on either side of Draco's head. Imagine them engulfed in the dragon's flaming exhalations.

Separation and position angle diagram
The two measures of a double star are separation and position angle (P.A. in the table below). The directions shown here are for an inverting scope, such as a Newtonian reflector. Other telescopes may have different field orientations.

If you start at the tail, which stands highest above the horizon around 10 p.m. local time in mid-April, by the time you reach the Lozenge, all the featured stars will have risen high enough for a good view. As we move into May, the entire constellation becomes fair game at nightfall.

I used a 10-inch f/6 Dob with an acid-dew-etched primary mirror and tube lined with several unreachable spider webs. Contrast isn't great in this scope, but it's a decent star-splitter. Since none of the listed doubles are closer than 0.9″ (arcseconds), a 6-inch should be able to tackle most of these.

  • ΣI 25 — We begin with an easy, bright triple star near the end of Draco's tail, not far from the former polestar, Thuban. The 6.6-magnitude primary star glows with a reddish-orange hue and forms a triangle with its 7th- and 9th-magnitude companions. With separations of 3′ and 1.75′ (arcminutes), this trifecta of suns is easy to resolve in any scope or even a pair of 10× binoculars.
  • Σ1878 — I love the challenge of prying apart close, unequal doubles. With a separation of 4.1″ and a difference of three magnitudes between primary and secondary, you'll want to use 100× or higher for a clear view of this sweet pair.
  • Σ1882 — This pair sits in the same medium power field of view as Σ1878. Use low magnification for this duo, the components of which shine at magnitude 7 and 9, separated by 11.4″
Itty bitty Eta
My sketch shows Eta Draconis as viewed through the 10-inch at 317×. The companion is faintly visible in good seeing just beyond bright Eta's diffraction rings. South is up.
Bob King
  • Eta (η) Draconis (OΣ312) — It's a demanding double! But if you hit it on a night of excellent seeing, the sight is unforgettable. At at glance, golden Eta (magnitude 2.8) seems to gleam alone. But parked just 4.4″ to its southeast and some 175 times fainter, the 8th-magnitude companion fights for its life in the glare of the primary. The contrast between the two is so extreme, I let out an involuntary wow when I finally coaxed this spark into view. Save Eta for a night when stars reveal delicate diffraction rings at high power. A magnification of 317× and a combination of averted and direct vision did the trick. Once seen and locked in the memory Eta gets easier next time around.
  • Σ2054 — Only 11′ from Eta and in the same medium power field of view, this pair of pearls is a beautiful sight. Although the tightest double on our list at 0.9″, I had no trouble at all separating the components with 317×. Magnitudes 6.2 and 7.1.
  • Σ2118 — These are twin 7th-magnitude beads separated by 1.0″. Another cozy couple similar to Σ2054 (above).
  • Psi11) Dra (Σ2241) — A beautiful, bright pair for low-power viewing. The 6th-magnitude secondary shines 30″ northeast of the 4.6-magniutde lemon-hued primary. The Washington Double Star Catalog lists two additional possible companions: magnitude 11 at 78″ in position angle (P.A.) 107°, and magnitude 13 at 106″ P.A. 66°.
  • Epsilon (ε) Dra (Σ2603) — An attractive unequal double (magnitudes 4 and 7) just 3.2″ apart. A close pair that's easy to resolve at 100× and up.
Equal doubles
Draco's two bright, equal doubles are must-sees. Nu is visible in binoculars, and Mu in a 4-inch scope at 100× and higher. These views are through my 10-inch Dob.
Bob King
  • Nu (ν) Dra (ΣI 35) — I love these pure white, equally-bright stars in my binoculars. They really shine at low power through the scope, too. There's something mesmerizing about seeing two bright, equal stars paired.
  • Σ2146 — A duo with a mystery. Sources list it as a triple with a 7th-magnitude primary and two 9th-magnitude companions. I can easily see one companion located 89″ to the southwest, but found no trace of the other, supposedly 2.6″ away. Based on the visibility of similar pairs I should have easily spotted it. What do you see?
Three for thee
The close pair 16 Draconis (below) joins 17 Draconis (top) to make a beautiful triple star. South is up.
Bob King
  • Mu (μ) Dra (Σ2130) — Another fine, equal double resembling Nu (ν) Dra but much more compact, with twin 6th-magnitude stars separated by 2.5″. At 254×, the split is comfortable, but I like the 76× view, where the two fiery lights nearly touch, better.
  • 16, 17 Dra (Σ2078) — A fantastic triple star and personal favorite. 16 Dra and its B secondary nestle together at  3.1″, while the bright C companion scintillates 90″ to the pair's south. Binoculars easily cleave A from C, but you'll need a scope to see all three. All gleam pure white.

Separation in the table below is measured from the primary (A) star to the secondary. Position angle is the direction from the primary to the secondary. "Year" is the most recent year in which the measurements were made.

A Dozen Draco Doubles 
Star
R.A.         Dec.
   Magnitudes Separation P.A.    Remarks Year
ΣI 25 13h 14m +67° 17' 6.6, 7.1, 8.9 179", 105" 296°, 223° Ruddy primary 2015
Σ1878 14h 42m +61° 16' 6.3, 9.2 4.1" 315° Pretty pair at 100x and up 2015
Σ1882 14h 44m +61° 06' 6.9, 9.2 11.4" Easy split 2017
Eta (η) Dra 16h 24m +61° 31' 2.8, 8.2 4.4" 143° Dramatic unequal pair! 2015
Σ2054 16h 24m +61° 42' 6.2, 7.1 0.9" 351° Beautiful, super-tight 2017
Σ2118 16h 56m +65° 02' 7.1, 7.3 1.0" 66° Close, equal duo 2017
Psi11) Dra 17h 42m +72° 09' 4.6, 5.6 30.1" 14° Gold primary, easy, bright 2017
Epsilon (ε) Dra 19h 48m +70° 16' 4.0, 6.9 3.2" 21° Gorgeous at 100× and up 2017
Nu (ν) Dra 17h 32m +55° 11' 4.9, 4.9 62.1" 311° Compelling in binoculars 2017
Mu (μ) Dra 17h 05m +54° 28' 5.7, 5.7 2.5" Exquisite equals 2017
Σ2146 17h 13m +54° 08' 6.9, 8.8, 8.9 2.6", 89.3" 224°, 235° 2nd companion easy split 2016
16, 17 Dra 16h 36m +52° 55' 5.4, 6.4 / 5.5 3.1", 90" 105°, 193° Dazzling triple — must see! 2017
Data are from Washington Double Star Catalog. Right ascension and declination are for equinox 2000.0

 

Comments


Image of Rod

Rod

April 17, 2019 at 12:00 pm

Very nice and some good double stars to view! Last night I was out enjoying Polaris as a double star with UMi B about 18" angular separation. I viewed at 129x, Polaris double stationary while Arcturus at 129x - zipped across the eyepiece field of view (about 0.56 degree). Houston, Earth has an axis and rotates 🙂 Bob, I hope to enjoy some of your double stars listed here soon, especially after we depart the Full Moon period.

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Bob King

April 17, 2019 at 10:02 pm

Thanks, Rod. Yes, indeed. Anyone who wants to experience Earth's rotation only has to look through a telescope.

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Curt-Nason

April 18, 2019 at 5:53 am

Plutarch or Ptolemy?

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Bob King

April 18, 2019 at 9:07 am

Thanks, Curt! Ptolemy of course 🙂

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Rod

April 18, 2019 at 7:53 am

Plutarch or Ptolemy? My answer is the telescope 🙂 I have been observing sunspot AR2738 since 07-April-19 when it first appeared on the Sun's east limb, rotating into view. Yesterday I observed the Sun again and noted in my stargazing log: "Observed 0745-0830 EDT. I enjoyed very good views of sunspot AR2738 and a smaller, unnumbered sunspot closer to center of the Sun this morning. 32-mm plossl and 14-mm eyepieces gave very good views with white light solar filter and #12 Yellow filter and #23A Red filter. The 14-mm at 71x and nearly 1-degree true field of view in the eyepiece was impressive looking at both sunspot areas and seeing the complete solar disk image in the eyepiece field of view. Distinct dark core for AR2738 with lighter area around the core region including light plage all around. AR2738 near 10:00 position much closer to west limb. North up, mirror reverse view in my telescope. The Sun rotates west to east, sunspot AR2738 moved westerly since appearing on 07-April-19 near the Sun’s east limb. The website, theskylive.com image for this morning shows the unnumbered, smaller sunspot and AR2738. I made periodic adjustments to altitude and azimuth controls because of Earth's rotation to keep the Sun centered in the field of view. Sunspot AR2738 is moving westerly across the Sun because the Sun rotates west to east. On Earth, the Sun rises in the east as well as the stars and they move westerly because just like the Sun, Earth rotates west to east on its axis..."

Telescopes clearly show the Earth rotates, the Sun rotates, Mars rotates, Jupiter rotates, etc. Observing with quality telescopes, we are observing large, round planets and the Sun that spin :). Good telescopes and eyepieces taken care of over the years, can bring a lifetime of enjoyment viewing. The Internet and social media today has videos and groups claiming the earth is flat, does not spin, does not move (immovable flat disk earth) and everything in the firmament moves above the same side of the flat disk earth where the Sun moves east to west shining like a spotlight over a limited area of the flat disk earth along with the Moon moving and planets, all on the same flat side. Telescope observations *flatly* disprove these Internet and social media hoaxes.

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David

April 24, 2019 at 10:29 am

This article about Draco is great, but it would help if the SAO numbers were given to help those who use "go to" scopes.

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Bob King

April 25, 2019 at 12:24 pm

Hi David,
Thank you for your comment. I will consider that the next time. I had hoped that the RA and Dec. coordinates would help point users of go-to scopes to the target stars. I'm not a go-to user myself — are SAO numbers a standard way for go-to users to navigate to a star? Thanks!

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Kerbal9

May 6, 2019 at 8:51 am

Thank you, Bob!
I really enjoy your articles.

What is this symbol "Σ" means? Is it some catalogue of binary stars? I have seen "Σ2054" as "STF2054", but Stellarium show it as "HIP 80309A".

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