More Pretty Double Stars
Seek out these lovely pairs when the Milky Way dominates the sky.
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.