Category: Deepsky observing

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The second object for the night was M 13, the big globular cluster in Hercules. The 21mm showed too much of the grayish sky, but M 13 was already resolved very well. The best view I got with the 7mm Pentax XW (230x). The cluster was completely resolved, even under these mediocre conditions. There were a lot of long streams of stars extending from the bright core. It looked more or less like a big spider. The three dark diverging lanes, which should look like a propeller, stayed invisible again. Probably I need a better seeing and a darker sky for this.

After M 13 I turned the dob toward NGC 6210 (Hidden Treasure 78 from Stephen J. O'Meara's book, Hidden Treasures). Already at the lowest magnification (76x) with the 21mm Denkmeier, this planetary Nebula looks like a deep-blue little disk. Using higher magnifications up to 230x made it look a lot bigger, still blue, but not so blue as with the lowest power. The seeing didn't allow higher magnification, so I could not go for the real details. According to Phil Harrington (The Deep Sky: An Introduction) this planetary takes high magnifications well, and is at its best 150x or more.

I ended my little tour with two objects I had never observed before, Hidden Treasure 94 (The Flying Unicorn Cluster) and Hidden Treasure 18 (The Ghost of the Moon) from the Additional list from O'Meara's latest Deep-Sky Companion. HT94 (NGC6709, Collinder 392), the Flying Unicorn Cluster, is a wonderful open cluster in Aquila. At low powers (78x) the triangular shaped cluster is very obvious, with some very nice groupings of (colored) stars. Although high magnification (230x) revealed more stars, I liked it most in the 12mm Nagler with a magnification of 133x. The cluster was nicely framed, some 40 to 60 stars with some "space" left around it. The colors came out even better than with the low power view, and I could detect quit a few "double-stars" or groupings of several stars; a very nice object, which I will definitely visit again under better conditions.

HT 18 (NGC 6781) from Appendix C (Twenty additional hidden treasures is) is a magnitude 11 planetary, about 2' in diameter. Without filters this big planetary is not so easy to see, but with the UHC filter in place it is a perfectly round, very bright and easy object. There should be some details visible at higher magnification, but because of the bad viewing conditions I did not try this last night, but again a very interesting object, which was completely unknown to me. At the moment this hidden treasure list is my favorite a perfect alternative for those who have done the Messier and Caldwell catalog. I will be back with more observing details on these interesting deep-sky objects, but I will need a darker and more stable sky. Until then, Clear Skies to all of you!

Oh, and the Denkmeier eyepiece is a perfect match for my 300mm f 5.3 dob. If you wear glasses or want a good eye-relief for any other reason, I can highly recommend this relatively small and compact eyepiece.


The Denkmeier 21mm eyepiece compared to the T4 12mm Nagler


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18. Trapezium (Theta Orionis, multiple star)
Constellation Orion (also known as the Hunter), magnitude AB 6.7 / 7.9 and CD 5.1 / 6.7, separation AB 8.8” and CD 13.4”, position angle AB 31° / CD 241°, RA 05h35m DEC -5°23’. This group of blazing young stars, known as the Trapezium, doesn’t need an introduction. The trapezium is a group of four bright white stars at the heart of the Orion Nebula. Even in my 85mm refractor at 30x I can see them as four individual stars, forming a trapezium. The magnitude 5.1 C component stands out from the other three fainter stars in the 85mm reflector. Under a real dark sky, I have seen the E and F component in my 8-inch TAL 200K using medium to high magnifications. This group of stars is just wonderful through almost every telescope.

19. Beta Monocerotis (triple star)
Constellation Monoceros (Unicorn), magnitude 4.7 / 5.2 / 7.1, separation AB 7.3” and BC 2.8”, position angle AB 132° and BC 106°, RA 06h29m DEC -07°02’. Sir William Herschel discovered Beta Monocerotis in 1781, and called it “one of the most beautiful sights in the heavens”, and I can only agree with him. I have been observing this wonderful triple in Monoceros on every possible occasion, just enjoying the view: three almost equally bright stars with the same blue-white color. The A, B and C component form a narrow triangle, and I never found another group of three stars that are so close together, equally bright and of exactly the same color. With my 8-inch telescope I use a magnification of 166x to get a real nice split.

20. Castor (Alpha Geminorum, Struve 1110, triple star)
Constellation Gemini (Twins), magnitude 1.9 / 2.9 / 8.8, separation AB 4.0” and AC 72.5” , position angle AB 68° and AC 164°, RA 07h34m DEC +31°53’. In fact, Castor is a system of six stars. Three of them are visible through amateur telescopes, the A,B and C components. Each of the three visible stars is itself a spectroscopic binary. The faint c-component is in fact a pair of red dwarfs orbiting each other, an eclipsing binary (variable star) designated YY Geminorum. Through my 8-inch telescope at 200x all three components look white.



Image from SkyTools2 by CapellaSoft, click to enlarge!



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14. Gamma Arietis (Struve 180, Mesarthim, double star)
Constellation Aries (Ram), magnitude 4.8 / 4.7, separation 7.8”, position angle 0°. RA 01h53m DEC +19°18’. Gamma Arietis was probably one of the earliest discovered double stars. Robert Hooke stumbled into it by accident, while following a comet in 1664. Last year, I observed quite a few interesting doubles in Aries myself, but the two white, almost equally bright stars of Gamma Arietis are my favorite. With my 8-inch telescope at 166x both the primary and the secondary look like sparkling white diamonds set against a jet-black sky.

15. Almach (Gamma Andromedae, multiple star)
Constellation Andromeda, magnitude 2.3 / 5.5, separation 9.8”, position angle 63°, RA 02h03m DEC +42°19’. Almach is in fact a multiple star with three components, but the C component can only be detected with larger telescopes. The primary star of Almach is a golden or yellow K2 or K3 type of star, the secondary looks bluish in my 8-inch, but there are many observers that detect a definite green color in the secondary.

16. Iota Cassiopeia (triple star)
Constellation Cassiopeia, magnitude ABC 4.6 / 6.9 / 8.4, separation AB 2.5” / AC 7.2”, position angle AB 230° / AC 114°, RA 02h29m DEC +67°24’. This is one of the finest triple stars that I have observed until now, and it is certainly the most beautiful in the Cassiopeia area. With the 8-inch Tal 200K at 222x I split Iota Cassiopeiae into a bright white primary with a slight hint of yellow, and two white companions showing a hint of blue.



Image from SkyTools 2 by CapellaSoft, click to enlarge!

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9. the Double Double (Epsilon 1, and 2 Lyrae, quadruple star)
Constellation Lyra (Lyre), magnitude AB 5.4 / 6.5 and CD 5.1 / 5.3, separation AB 2.6” and CD 2.3”, position angle AB 357° and CD 94°, RA 18h44m DEC +39°40’. The Double Double was the first double/multiple star system I observed with my 8-inch Klevtzov in 2001, and until now the views I got that particular night were the best I ever got from this celestial gem. It was late in august and it had been a very hot and humid day. Around midnight, the outdoor temperature was still above 20 degrees Celsius. There was absolutely no wind and during the daytime, the sky had looked milky-white. During the evening, the air felt heavy and around midnight, the night-sky looked hazy, somehow covered in high cirrus clouds. It seemed useless to get the equipment out for observing, but I just got my new telescope and I couldn’t wait to give it a try. When I pointed the 8-inch TAL at the Double Double, I was stunned by the view. At 166x I saw four bright white stars, of almost equal magnitude, grouped in pairs, two by two. The image looked like the stars where frozen in their position. There was absolutely no movement, no shimmering stars. Both doubles were split perfectly. Later I realized that for observing close double stars, the conditions must have been nearly perfect that night. I observed the Double Double again and again over the last few years, but I never managed to get the same wonderful views I got on that hot night in august 2001.

10. Albireo (Beta Cygni, double star)
Constellation Cygnus (Swan), magnitude 3.1 / 5.1, separation 34”, position angle 54°, RA 19h31m DEC 27°58’. In 1978 I followed a course “Astronomy for beginners” at the local astronomy club. The course started in the last week of august and after every lesson, we would go outdoors and look at a few objects through a 4.5-inch reflector. I remember looking at the Andromeda Galaxy, the Double Cluster in Perseus, M13 and ………. Albireo. Until then I had never seen a double star through a telescope, let alone a colored double star! Ever since, I have been looking at Albireo on every possible occasion, with all binoculars and telescopes I ever owned, and I still love to observe this simply beautiful object, even after all these years. Through my 8-inch at 66x the primary, a type-K star, looks golden or yellow. The secondary, a type-B star, looks blue. The contrast, color and brightness of both stars is striking, and this magical double star should be at the top of everyone’s observing list. It is one of the easiest doubles to find and, for me personally, the most beautiful to look at.

11. Omicron 1 and 2 Cygni (31 and 32 Cygni, multiple star for binoculars)
Constellation Cynus (Swan), magnitude 3.9 / 3.9, separation 1°, RA 13h6m DEC +46°44’ (coordinates for Omicron 1). Now this is my favorite multiple star (or group of stars) for binoculars. Through my 15x80, Omicron 1 and 2 Cygni look like two bright orange stars, separated about 1° from each other and of almost equal magnitude. Omicron 1 (31) Cygni is a visual triple itself. About 5’ to 6’ away to the northwest of the orange primary, at a position angle of 323°, I see a bluish (magnitude 4.8) companion and about 100” to the south I see a white (magnitude 6) star at a position angle of 173°. Together, Omicron 1 and 2 Cygni form a wonderful group of four stars to observe with binoculars.

12. 61 Cygni (Struve 2758, double star)
Constellation Cygnus (Swan), magnitude 5.2 / 6.1, separation 30”, position angle 150°, RA 21h07m DEC +38°45’. This is a wide double, which can be separated even in small telescopes and binoculars. Because of their more or less equal brightness, I managed to split 61 Cygni with my 7x50 Bresser mounted on a mirror mount. I never managed to split Albireo in my 7x50, although the angular separation of Albireo is wider (34”), than from 61 Cygni. This is probably caused by the magnitude difference. While Albireo’s components differ about two magnitudes, the brighter A component overpowering the fainter B component, the difference between the 61 Cygni components is only 0.8 magnitude, making it easier to “see” both the primary and secondary as separate stars at low powers. In my 15x80 both the primary and secondary of 61 Cygni look chrome-orange, with a hint of red. Again another celestial gem that shouldn’t be missed!



Image from SkyTools2 by Capellasoft, click to enlarge!
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6. Epsilon Boötis (Struve 1877, Mirak or Izar, double star)
Constellation Bootes (Herdsman), magnitude 2.9 / 4.9, separation 2.8”, position angle 339°, RA 14h45m DEC +27°04’. In Bootes and the neighboring constellation Corona Borealis I observed quite a few double stars, but Epsilon Boötis, nicknamed Pulcherrima (in Latin: the beautiful) by F. Struve in 1829, is definitely my favorite. Through my 8-inch TAL at 166x this wonderful double has a bright yellow primary and the secondary is white with a slight hint of blue or green. I cannot decide on the color of the secondary. Which color do you see?

7. Ras Algethi (Alpha Herculis, double star)
Constellation Hercules, magnitude 3.5 / 5.4, separation 4.7”, position angle 107°, RA 17h15m DEC +14°23’. This beautiful double in the lower right part of Herculis is again a really good example of the simple beauty of double stars. Through my 8-inch TAL at 133x the primary is orange and the secondary looks white with a hint of green. Now, I know that there are no “green stars”, but it’s just the way the secondary of Alpha Herculis looks to me through the eyepiece. Color perception depends on a lot of different factors, the contrasting colors of stars being one of them. But also the equipment, the local seeing, and last but not least the observer, and the condition he is in, have an influence on color perception. I noticed during star parties and observing sessions with other observers from the local astronomy club, that observing star colors is a very subjective, personal matter. What looks green to one person looks blue to the other. You get the same discussion with yellowish stars. Some see them just as plain white, others as yellow, golden or orange, and some even see them as red.

I can only give you the advice to record the colors what you observed yourself, no matter what others claim to “see” . Write down your own perception in your observing log. Again, seeing colors is a very subjective thing. You best remember your observation, if you write down what you saw, not what others tell you they saw.



Image from SkyTools2 by CapellaSoft, click to enlarge!

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Anyway, I always have been a visual observer of the deepsky, and I just love these little gems for their aesthetic beauty. So here is my personal top 20 of double and multiple stars (until now), including basic data (constellation, magnitude of all components, separation, position angle, the RA/DEC (right ascension / declination coordinates), some background information, what to expect at the telescope and or binoculars, and of course finder charts for all 20 stars.

I present my 20 favorite double / multiple stars in five consecutive articles, for every time of the year a separate one, starting with early spring constellations and ending with winter constellations. The articles will be published in this blog within the next 6 weeks, starting today. So if you are interested in observing some wonderful double and multiple stars, hop in every now and again to read or print out the series of articles. With this first article, you can start observing double and multiple stars tonight. Clear skies!

My 20 favorite double stars part 1: early spring

1. Iota 1 Cancri (Struve 1268, double star)
Constellation Cancer (Crab), magnitude 4.2 / 6.6, separation 30.5”, position angle 307°, RA 08h54m DEC +28°46’. Cancer is a very faint constellation, but it holds some great open clusters and double stars. Most of you will know M 44, the beehive cluster and M 67, another fine open cluster in Cancer. But at the northern end of the crabs figure you can find iota Cancri, my favorite object in this barely noticeable constellation. Iota Cancri is a magical double, and it could easily be called the “Albireo” of spring. In my 8-inch at 100x it is an striking golden-blue pair of stars. Wonderful! A hidden treasure of the night sky that should be on everyone’s deepsky observing list.

2. Algieba (Gamma Leonis, Struve 1424, double star)
Constellation Leo (Lion), magnitude 2.2 / 3.5, separation 4.4”, position angle 127°, RA 10h20m DEC +19°51’. The name of this star could be from the Arabic “Al Jabha”, the forehead or from the latin word “iuba(e)”, the manes (of the lion). Algieba is the brightest star in the lion’s mane. It consists of a very close pair of stars, but I split the double at 133x with an 8-inch telescope easily. Both the primary and secondary look yellow to me. If you have a small telescope and find it difficult to split this close double, try it in twilight or with moonlight. This often seems to help with splitting bright close pairs, because the glare of the star is reduced. I even read a report from a German observer who got the best results by observing Algieba in a clear blue autumn sky in broad daylight, using a 63mm telescope. To be honest, the only star I ever saw in daylight was the Sun, so maybe I should give it a try.

3. Cor Caroli (Alpha Canum Venaticorum, Struve 1692)
Constellation Canis Venatici (Hunting Dogs) magnitude 2.9 / 5.5, separation 19.4”, position angle 229°, RA 12h56m DEC +38°19’. Cor Caroli, the Heart of Charles, marks the position of one of the two hunting dogs, Chara. Beta Canum Venaticorum marks the other dog, Asterion. Cor Caroli is a fine double and very easy to split in small telescopes. In my 4-inch refractor (TAL) at 83x I definitely see two white stars of unequal brightness. Others report two yellowish stars. Which colors do you see? If you’re not sure, turn the focuser slightly until the stars are out of focus, looking more or less like disks, making color detection easier.

4. Mizar and Alcor (79 Zeta Ursae Majoris and 80 Ursae Majoris, double star)
Constellation Ursa Major (Great Bear) magnitude 2.4 / 4.0, separation 708”, position angle 71°, RA 13h24m DEC +54°56’. Alcor and Mizar both can be seen with the naked eye from my suburban backyard, and it was the first double I pointed my very first telescope (a 4.5 inch reflector) at in 1978. In this small telescope, Alcor and Mizar were both separated widely and placed in the opposite ends of the field of view, and to my surprise Mizar was a double star itself. Mizar’s secondary with a magnitude of 3.9, can be seen at a position angle of 150° and the separation between Mizar A and B is 14.4”. To me, Alcor, Mizar A and B all appear to be white.


Image from SkyTools2 by CapellaSoft, click to enlarge!


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