More Pretty Double Stars
Seek out these lovely pairs when the Milky Way dominates the sky.
In "Pretty Double Stars for Everyone" I presented 42 double or multiple stars chosen for their beauty. When summer arrives in the Northern Hemisphere, another 54 gems become prominent. I hope you will agree with me that the two lists represent some of the most beautiful doubles and multiples visible.
The table on the last page has a couple of novel columns: color difference and optimum magnification. The color-difference rating refers to how far apart the two components are on the well-known OBAFGKM scale of spectral classification. For example, the blue and yellow stars of 24 Comae Berenices are class B and K respectively, yielding a color difference rating of 4. The final column suggests an optimum magnification.
Experience has shown me that doubles look best when viewed at a magnification determined by dividing 750 by the separation of the pair, given in arcseconds. For example, the components of the star Kappa (k) Herculis, also known as Marfik, are separated by 27.1 arcseconds; thus the optimum magnification is 750/27.1, or approximately 28x. The optimum magnification is typically about two and a half times the minimum required to resolve any given pair.