…continuedPretty Double Stars for Everyone
Some Double Star Details
The list on the following page is my compilation of the prettiest doubles (and multiples) visible from the Northern and/or Southern Hemispheres when Orion is riding high in the sky. The list has a couple of novel columns: color difference and optimum magnification. The color-difference rating is the number of letters between stars on the well-known OBAFGKM scale of spectral classification. For example, Almach's components are B and K, so Almach rates a 4. (In "More Pretty Double Stars" I present 54 double or multiple stars visible during summer in the Northern Hemisphere.)
It has been stated that the maximum magnification is about 50 times the aperture in inches. But you'll often benefit by going higher when viewing tight doubles. I begin by finding the star with my scope set at low power (which is also the maximum field of view). Then I work up to the optimum magnification.
The theoretical resolving limit of a high-quality telescope is about 5.5 divided by the telescope's aperture, in inches. But in all my years of double-star observing, I've never achieved this limit. So don't be disappointed if you don't either. Atmospheric turbulence will also play its part in reducing your ability to resolve tight doubles save the closest pairs for nights of steady seeing.