Everyone knows this star. We split each of the pairs many a time in a never-ending test of our scope’s optics. So what is it doing here? Read on....
In the October 1999 REFLECTIONS I indicated it was possible to split the stars Omicron 1 Cygni (mag 3.8) and 30 Cygni (mag 5) using only your own keen eyesight. At 5.5 arcmins of separation I thought that was an impressive split. In the January 2000 REFLECTIONS I indicated an even better naked eye split. The tiny pair in the handle of the Pleiades (the seven sisters, M45) open star cluster it is possible to split the 5 arcmin pair of 27 Tauri, or Atlas at mag 3.6 and a 5th magnitude star known as 28 Tauri, AKA Pleione. Not bad; but wait, it gets better.
One mid-June evening I was outside panning around for Comet Linear S4. The comet was suppose to be a magnitude 7 and I figured I could sweep it up in my 7 x 50 binoculars. Well I didn’t find it. Not to waste the evening I decided to move over to Lyra and place the glasses on the Double-Double. Yep, It’s still there I thought. Bring the binocs down and with my eyes still on the star I watched it for a moment, then all of a sudden it split. Right there before me. I split it again and validated my observation by confirming the orientation of the pair.
I thought how could this be? We are not supposed to split something that close. Rushing in the house I decided to consult Burnham’s Celestial Handbook. According to this source Epsilon’s pair is separated by about 3.5 arcmins and may be seen as a double “by very keen eye unaided.” Wow! Since then I have located other sources confirming this (American Nature Guides - Astronomy, Ian Ridpath, Sue French’s Lyre Lessons in Sky & Telescope’s September 2000 issue).
It should be mentioned that a high-pressure front had recently past through our skies, cleaning out all the upper level junk and I had partially dark adapted my eyesight prior to making this observation. When making this observation the pair should spilt only momentarily, in those brief instances of steady seeing. I don’t believe I have “keen” eyesight, just a persistent observing technique that most seasoned observers with decent long-range vision can duplicate. Try warming up your eyeballs by splitting Delta 1 (mag 5.5) and Delta 2 (mag 4.5) near by. Go back to Vega; turn southeast past near by Zeta and on to the 10-1/2 arcmin double star Delta. It just slightly further apart from Zeta as Zeta is from Vega. So try this yourself, let me know how you far, and don’t forget to dark-adapt your eyesight.