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My 20 favorite double and multiple stars, part 2: late spring – early summer
5. Polaris (Alpha Ursa Minoris, the North Star, the Pole Star, double star)
Constellation Ursa Minor, (Little Bear), magnitude 2.0 / 8.2, separation 18.4”, position angle 218°, RA 02h32m DEC +89°16’. This star is without question one of the best-known stars in the sky, but I wonder how many people know that Polaris is also a very nice double star. Through my 8-inch TAL at 133x, the primary looks yellow and the much fainter secondary looks white. Use medium to high magnification (at least 100X) to split the faint secondary from the bright primary. At low magnifications the secondary is lost in the glare of the primary. If you have an equatorial mount, you might find it difficult to get Polaris into view. You should polar align your mount exactly, or simply turn your polar axis about 90 degrees to the east or west, using your mount more or less as an alt-azimuth mount, and it shouldn’t be too difficult to get Polaris in the centre or the eyepiece. I use the exact polar align method.

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.

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Image from SkyTools2 by CapellaSoft, click to enlarge!


Posted by Math on 05/09 at 07:25 PM
Deepsky observing • (3) Comments • (0) TrackbacksPermalink

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.

Posted by sanat  on  06/24  at  04:21 AM

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