LCAS Observer Challenge - April 2005
Dave Wagner
I like double stars. You can view them from light polluted skies with any aperture and any scope and always get delightful views.
While the Observer Challenge has only a small number of doubles on its list, over three quarters of the stars in the skies above us have companion or multiple companion stars.
Our first list double, Algieba (? Leonis), located on the sickle asterism of Leo, is a gold-gold star pair, with a tight spacing of less the 5". The proximity of these two stars tends to enhance the differences in their colors, and you may see them as more orange-yellow or yellow-green (more on this color variability later). At a distance of 120 lights years, these 3rd and 4th magnitude stars are true giants, no longer fusing hydrogen in their cores.
24 Comae, the second challenge double, is about 270 light years distant. Once considered part of the tail of Leo (now Coma Ber-enices), 20" apart, at magnitudes of 6.7 and 5.2, they consist of a contrasting color orange-emerald pair.
Observing Methods - A com-mon method to observe the color of a double involves putting the stars slightly out of focus. This spreads the color and gives you a larger image to evaluate. Another method is to observe the color with both stars in the FOV, then separately (one star out of the field of view). You may see different coloring, dependent on the presence or absence of the contrasting star. Finally, just as with dim galaxies, there are those telescope 'tappers' out there, who suggest a little jiggle of the scope helps the eye to best discern the colors. Give it a try.
So, just what color is it? - In the November Night Times I reported my observation of another challenge dou-ble, Almach, as a wonderful yellow-GREEN pair. There is no mechanism to cause a green color emission from a star, so how do we explain a green star or the variance of perceived colors by individuals? Here are some suggested causes, as put forward by Paul Baize, a renowned French double star observer.
Complementary Colors - Look at a bright red object for a while, and then look at a white sheet of paper. You'll see the object, in its complementary color on the paper! Looking at one star, and then looking at the other, the color perceptions can be transferred by your visual neurons in a complementary fashion affecting the perceived color. In a similar manner, observers report that Saturn looks more 'green' when in the same field of view as Mars.
The Purkinje Effect - At low inten-sities color is absent in our perception, and different colors are first detected at different intensities. For low intensities we may perceive an unbalanced mix of colors due to the low intensity of the light. Basically our eyes are working in an environment where color is at the very edge of detectability.
All eyes are not equal - 7% of men have a red-green color blindness. I noticed at my last eye doctor testing those little colored numbers in that color blindness test didn't stand out as much as they did when I had younger eyes. Basically none of us can color calibrate our eyes. In the end, double star colors may make for some interesting science questions, but their true beauty is truly in the eye, and the eyepiece of each beholder.
Go to http://tinyurl.com/67afd for some great double star drawings and listings.
