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Spring Double Star Tour

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In the north woods, Spring comes much later than in most places, but it generally starts near the end of April. By then the only remaining evidence of winter are patches of snow left in the woods beneath the shade of thick evergreens. The smelt are beginning their yearly trek up stream, and it won't belong before the Rainbow Trout follow. Black bear also make their appearance emerging from hibernation to forge for the remains of fall's harvest. These fury scavengers are closely followed by another species ending their long winter's rest – the amateur astronomer. Clear spring skies and warming temperatures have lured him from his cozy study and has drawn him away from his beloved astronomy library. He's hungry and a host of celestial delights wait to be devoured. Included among them are some outstanding double stars. Let's take a look at what's on the menu each Spring.

The double stars I have chosen from many dwelling among the spring constellations are some of the most beautiful or interesting or both. Sixteen specimens are listed by right ascension and a small finder chart and drawing are made for each. My hope is that you will enjoy them enough to include double stars as a regular part of your observing list in the future.

The Target List

As you look over the target list, you might notice that all the primary stars are bright enough to be seen with the naked eye from a dark viewing site, I can see all of them from front yard on dark moonless nights. This should help the beginning observer, in that he can put his red dot, crosshair, or bullseye right on the target. From a less-than-dark site you'll need to star-hop from the stars you can see. Also, you should be able to split all the pairs in a 3" telescope and most in a 2"; that puts them in the range of the equipment of almost every beginning observer. I am able to split all of them with my 80mm f/15 achromat refractor, though some present a challenge that requires steady seeing.

The constellations I have included are: Bootes, Cancer, Canes Venatici, Coma Berenice, Gemini, Hydra, Leo, Lynx, and Ursa Major. Again, they are all visible from my observing site at 46°+ latitude, so they should be easy from most locations in the Northern Hemisphere. The star charts were made using Guide astronomy software and the drawings were made using Adobe Photoshop. With the drawings, I tried to give a good idea of what you will see at the eyepiece, however, the orientation of the two stars may differ from the drawing, depending on what equipment you are using.

The Targets

Let's begin with Gemini in the West and work our way toward Bootes in the East

William Tyler Olcott called our first double in Gemini, Castor, "the gem of double stars ..... considered the finest specimen of a binary in the northern hemisphere". He may have been referring to the comments of Sir John Herschel who described Castor as "the largest and finest of all the double stars in our hemisphere and that whose unequivocal angular motion first impressed on my father's mind a full conviction of the reality of his long cherished views on the subject of the binary stars." Alpha Geminorium was the first star that provided William Herschel with certain evidence of a binary structure. It is also quite beautiful. Olcott saw both to be yellow white, while Smyth saw no color. Charles Worley called it "a remarkable multiple system" and Paul Couteau says it is "one of the brightest pairs in the sky. A good test for a small refractor." They are a lovely pair in my 80mm at 100X, with the secondary showing a pale pinkish orange. There is also a "C" component 72" away at 165° p.a. Given their historical significance they are indeed as Camille Flammarion puts it: "an important orbital system".

Three and a half degrees to the south is our next double – Kappa Geminorium. It is a delicate pair in which Olcott saw an orange primary and pale blue secondary. Smyth agrees this time and so do I. Dembowski suspected that the companion might be variable, but Crossely in his "Handbook of Double Stars" attributes the change in the companion's glow to the light from the bright primary star. Because of the difference in magnitude, this is one of the difficult doubles in the tour for my 80mm to split and this despite it having 7 arc-seconds of separation. You will need dark skies to split this in a small telescope and don't be afraid to try magnification over 200X. Otherwise, try a 6" or larger scope.

Our third double in Gemini, 38, is 5° southeast of gamma Geminorium. It splits easily in the 3" at 100X into a yellow-white primary and yellow-orange secondary. Olcott saw the secondary as blue and commented on the fine contrast of the pair, while Smyth called it "a neat double star' of "light yellow and purple." He says that this "very fine object" has "colours so marked, that they cannot be entirely imputed to the illusionary effect of contrast"; quite a compliment coming from such an experienced observer. Couteau says that "according to Flammarion the companion varies in brightness and color. While the primary is golden yellow, the companion changes from green to blue, purple and red." This seems to agree with the different colors noted by different observers. What colors do you see?

We now move further west to the constellations of Cancer and Hydra. Cancer yields two doubles to the tour, while Hydra just one.

Iota Cancri is a pair of very fine contrast. Olcott saw the pair as yellow and blue and Smyth - orange/clear blue. It is lovely in the 80mm at 67X and appears yellow-orange and blue-green. Flammarion noted a pair "pale orange and blue, of beautiful contrast", and Couteau suggests "looking at it with a pair of binoculars". With a separation of 30.8" it is the second widest pair in the tour.

13 degrees southwest of Iota is Zeta Cancri. It appears to form a naked eye double with a companion star just 28' to the east, but these stars are unrelated. A closer look at around 70X, reveals pair of yellow-white and yellow-orange stars. It is actually a triple system, but only two components (AB and C) are visible in a small scope. Olcott saw them as yellow and orange, but Herschel listed them both as pale red. While Struve saw different shades of yellow, he remarked that these varied over time and Dembowski noticed the change also. Agnes Clerke in her book, "The System of the Stars", discusses the variation of color in doubles and in doing so mentions Zeta Cancri. She wrote: "The three stars of Zeta Cancri are usually yellow, but Dembowski noticed them as all white in 1854-56, the remoter component turning yellowish or olive in 1864-65. This form of concordant change through various shades of primrose or cowslip is not very rare among revolving stars while the development of colour in other pairs tends toward the production of contrast. It often happens, too, that one component only varies in hue, in which case the change always affects the satellite star." This system is unusual in another sense. According to Smyth, William Herschel had declared this system to be "a most minute treble star", but later his son John and James South felt that the primary component was a single "beautifully defined and round" star. However John South, on later inspection saw the primary component to be "unquestionably elongated" and a lengthy investigation by J. Herschel, South, Dawes and Smyth followed; eventually it was noted as triple star. Flammarion later called it a "remarkable ternary system".

Next we travel south of Cancer to the head of the sea serpent – Hydra. Epsilon Hydrae is a difficult double to split in a small scope. Though under dark skies and using 170X the dim secondary © can be seen nearly touching the bright primary (AB); both showing a yellowish tint. Olcott calls Epsilon Hydrae "a very interesting star. It was discovered to be double by Struve and in 1888 Schiaparelli noted that the brighter component was itself a close double." Smyth said that by the time Struve discovered it in 1830, it was just over 3" in separation and Dawes wrote at the time: "Indeed, were the small star visible fifty years ago, as it is now, it never could have escaped Herschel." Yet Crossley later wrote in his handbook: "It is extraordinary that this beautiful star should have escaped the scrutinizing eye of Sir Wm. Herschel." With the large instruments that Herschel had at his disposal, I too find it hard to believe. Anyway, Flammarion calls it "yellow and blue, a charming orbital system", and that it is.

Another tight double awaits us just 10 degrees northeast of Iota Cancri in the tail of the Lynx. A little north of Alpha Lyncis is the 4th magnitude star, 38 Lyncis. It will take in excess of 200X to separate this double into what I see - a green-white and pink-yellow pair. Smyth saw "silvery white and lilac" and Crossley – "white and blue". Again, a dark and steady sky will help, but don't be afraid to turn up the power; it will be well worth it!

A larger cat than the Lynx awaits us next, as we turn our attention to the much more recognizable figure of the Lion.
Leo has some outstanding double stars and we have three of them on the tour, beginning with Gamma Leonis. The renowned double star observer F.G.W. Struve called Gamma Leonis the " finest double star in the northern sky"! It is an outstanding pair. Olcott calls it the "telescopic feature of the constellation. The colors of the two stars are yellow and green". At 120X in the 80mm, they are something special in different shades of gold and compete for the best double of the tour. It is a bright pair and thus the comment by Olcott that they are "best observed when it is not quite dark or in moonlight". This helps dim the brightness and to enhance the colors. Struve saw his favorite double as golden and greenish red, while both Wm. and John Herschel saw a reddish white pair. Smyth on the other hand comes closer to my estimation seeing bright orange and greenish yellow. This is definitely a highlight of any observing session and has such adjectives as "finest", "beautiful" and "splendid" attributed to it by some of the most astute double star observers. However, I think Flammarion best describes Gamma Leonis when he calls it, " two yellow translucid diamonds".

Just 9.5° northeast of Gamma is 54 Leonis. It is the bottom star of a triangular asterism. Though not as spectacular as our previous double, Olcott calls it " a fine object" and it is a bit easier to split in a small scope with a separation of nearly 7". Both Wm. Herschel and Smyth saw no color, giving white and gray, yet they call is "beautiful" and "neat", respectively. Not spectacular in my in my 80mm at about 70X, but "neat" and the surrounding asterism is "neat" too.

The third binary in the constellation Leo, Tau Leonis, is the widest pair in the tour at nearly 90 arc-seconds and is therefore a welcome break from the tight doubles we have observed so far. It is located about 13 degrees SSW of Beta Leonis, the brightest and most southern member of an arc of four stars. Listed as a binocular double in some references, it is an easy pair to split. Olcott saw them as "Lemon and light blue. A field glass object". Flammarion is one of the few others who comment on it, writing, "an isolated pair, easy in small instrument". So the challenge may lie more in locating the pair than in splitting it.

From the Lion we travel way up north to the Bear. Living where I do, I am able to enjoy this constellation all year long, but in the spring it is directly overhead and strutting it's stuff. Our only double on tour from this area is Zeta Ursa Majoris, but what a fine specimen it is! Mizar, as the ancients named it, is one of my all time favorite double stars. Olcott calls it "the best known double star in the heavens and one of the most beautiful". It is also the first double star discovered, Riccioli doing so in 1650. It was also the first double star to be photographed, Bond accomplished that 200 years later in 1857. As a double star it has an abundance of significance. In fact C.E. Barns designated Mizar a "pioneer star" which "never fails to inspire awe, however frequently observed". Mizar is paired, though not physically with another naked eye star just 11' 48" away, Alcor. Through history they have been called the "Horse and Rider" and as a pair they were said to be at one time, a test of good eyesight. Today both are readily seen without aid, sitting in the middle of the handle of the asterism called the "Big Dipper" or "Plow" and therefore, as Agnes Clerke writes, their "gradual brightening is thus strongly suggested." Under closer scrutiny, Zeta Ursa Majoris shows itself to be a fine binary star with primary and companion both brilliantly white. In my 80mm at about 70X, Mizar, its companion and Alcor can be seen together in the same field and present a stunning sight and I would recommend viewing them at this magnification. Paul Couteau agrees and writes, "it is good to look at Mizor and Alcor in the same field, as one can with the smallest refractor, to compare the separations". In other words it gives the observer a good estimate of the separation that is required for a "naked-eye" double.

We're on a roll, so let's continue that way with our next star, another contender for the "best of tour". It is located just 17 degrees south of Mizar in the constellation of Canes Venatici – "the Hunting Dog". I don't think the Bear has anything to worry about, as the "Dog" isn't much, but this shapeless constellation allows our next double to stand out like a sore thumb or should I say "paw". Alpha Canes Venatorium is a splendid double star. It was given a name, "Cor Caroli" or "the Heart of Charles", by Astronomer Royal Halley in 1725 to honor King Charles of England, but there is some dispute as to whether it was Charles I or Charles II he was honoring. Olcott gives yellow for both and Smyth – "flushed white and pale lilac", while C. Flammarion calls it "one of the prettiest doubles in the sky, golden yellow & lilac". This is close to what I see; in my 3" at 120X - yellow white and pinkish blue. Clerke gives an interesting description, calling them "pale yellow & fawn". It is a fine contrasting double that floats like two jewels in an otherwise featureless area of the sky.

Next, we move farther south into a region rich in galaxies. In among the spirals we search for a fifth magnitude star in the constellation, Coma Berenice. It is the star designated 24 Coma Berenices. You are going to have to use the star chart to locate it nearly 20 degrees SSW of Cor Caroli. Once located, it is easily split by a small scope into two beautiful stars. The colors are very pleasant in my 80mm at 40X, showing great contrast between the orange primary and green secondary. Olcott saw "orange and lilac" as did Flammarion, while Smyth gives "orange and emerald", calling "the colours very brilliant". The secondary is not actually green, but this appearance is a result of its close proximity with the primary star. But who cares, it is still a beauty to behold.

Our last constellation, Bootes, holds three of the tour's double stars. Two are easy to locate and all present fine targets. Lets begin with the hardest to locate, 39 Bootis. It is not that difficult, just move 10 degrees due east of the end star in the Big Dipper's handle, Alkaid. 39 Bootis is a 6.3 magnitude star that shows a yellow white primary and secondary of nearly equal brightness at about 140X in my small refractor. At a separation of around 3 arc-seconds, they appear as a pair of headlights from some alien spaceship. It is interesting that Olcott doesn't give any description other than they present "a fine contrast of colors" and Flammarion also gives no colors, while Smyth mentions "white and lilac". Check them out for yourself, I'm sticking with yellow-white headlights.

To find the next double on the tour, locate Arcturus, the bright yellow zero magnitude star that cannot be missed. Move just 6.5 degrees east and a little south to the 5th magnitude Pi Bootis. At 111X it is clearly split. Flammarion called it a "charming couple" and I would agree - a pretty pair of two nearly equal white stars. Sir John Herschel reported them as, "Nearly equal; large is white; the smaller perhaps inclines to blue" and Olcott gives "both white". Herschel is often credited with its discovery, yet interestingly, Crossley writes in his handbook: "Herschel wrote: 'Sept. 20, 1879, Mr. Rev. Hornsby told me it was a double star and I found it to be so.'"

Our final double lacks no description of color. Epsilon Bootis is easy to spot along the eastern side of the Herdsman shining at magnitude 2.5. Olcott calls this "a superb object, a test for a 2 inch glass. Called "pulcherrima" by the elder Struve on account of its extreme beauty. Yellow and bluish are the colors attributed to its components." In a paper, dated 6/9/1803, William Herschel stated: " This beautiful double star, on account of the different colours of stars of which it is composed, has much the appearance of a planet and its satellite, both shining with innate but different light." Herschel knew this star well. In 1782, Epsilon Bootis was the object of his investigations for stellar parallax, though they were unsuccessful. Years later he recognized its binary character. He gave reddish and blue or lilac for the colors, and his son, John Herschel, saw yellow and blue green, while Struve gives yellow and green and Smyth – "pale orange and sea-green, the colours being distinct and strongly contrasted. This is a lovely object." I see gold and slate blue in my 3" at about 200X and rank this as another "best of tour". Flammarion agrees with me and gives "bright yellow and marine blue". Whatever colors you see, they are bound to be breathtaking.


The word "Pulcherrima" is of Latin origin and means beautiful. Struve used the descriptive label for the star Epsilon Bootis. No doubt he was enamored by the striking physical beauty of this pair of diamonds floating through space in unison. However, I can't help thinking that there was more than just the visual appearance that attracted this observer to them. I have to believe that much of their beauty stemmed from the truth that they revealed to him about the physical laws of the universe. Truth has an apparent beauty, every bit as attractive to us as the sights that please our eyes. Einstein once remarked about his theory of relativity: "It is too beautiful to be false". When investigation and discovery reveal truth about the world in which we live, it awes us as much as snow-capped mountains or a starry night.

That concludes the "Spring" tour. As the weather warms, get out and take in the sights, you'll enjoy them. I know I look forward to seeing these familiar visitors, each year after my long winter's nap comes to an end.

  1. The Bedford Catalog - Wiliam H. Smyth (1844)
  2. Field Book of The Skies - William T. Olcott (1929)
  3. In Starland with a Three-Inch Telescope - William T. Olcott (1909)
  4. Observing Visual Double Stars - Paul Couteau (1923)
  5. Stars and Curiosities of The Sky - Camille Flammarion (1882)
  6. A General Catalogue of 1290 Double Stars - S.W. Burnham (1900)
  7. A Handbook of Double Stars - Crossley, Gledhill & Wilson (1879)
  8. The System of Stars - Agnes M. Clerke (1905)
  9. A Popular History of Astronomy During the 19th Century - Agnes M. Clerke (1879)

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