In my thread in the refractor forum (From 11-inch SCT to APO -Options), I have just reported on the first night's observation of double stars with an Astro Tech AT115EDT APO refractor.
I was able to observe over a dozen nice double stars, the closest of 2 arc-seconds separation or less. One double Zeta Bootis, reportedly of 1 arc-second separation (a test for a 115 mm aperture) was at best elongated. While the components are of equal brightness (magnitude 4.5) seeing wasn't perfect. By way of comparison 50 years ago I was able to resolve this pair with my home made 8-inch Newtonian reflector. My observing log for August 30,1967 noted "1.1 arc-second; easy to resolve, image jumping in field; sometimes multiple images, each of which is double". Of course for an 8 incher that double was well within its capability, even on a night of questionable seeing.
But in defense of the 115 mm APO, SkySafari says that Zeta Bootis has a very eccentric orbit with a period of 123 years. At closest approach (3 years from now in 2021) the pair are "visually inseparable". Also they are easily separated at the widest separation (in 2082). The last time they were at widest was in 1959 (2082 minus 123 years). My 1967 observation was just 8 years later. My little APO refractor was at a great disadvantage in trying to resolve this double in 2018.
But for last night's observing with the little APO refractor I was able to employ powers up to 230X (50 per inch of aperture). The observing experience was not approached from a viewpoint of which of my telescopes gives a “better” image. Rather I was just enjoying what this little APO refractor can deliver. But Zeta Bootis was too much to ask of it.
Has anyone else had experience with Zeta Bootis, either recently or some time back?
"The stars loop about each other on hugely elongated orbits, which carries them from (from the computed orbit) 64 Astronomical Units apart (half again Pluto's distance from the Sun) to a mere 1.4, close to Earth's distance, which is close to a record for such ellipticity. The double thus is separable by telescope during farthest separation, and quite inseparable at close passage, which occurred in 1897 and which will take place again in 2021. Your best view will come in 2082. With a stellar invasion like this one, no planets would be at all possible. The large eccentricity suggests some kind of violent encounter with another star. Perhaps a third member was lost in the process. We will never know."
Information like this is what makes astronomy in general and double star observing in particular so fascinating. While I find equipment forum discussions to be interesting, it's observing celestial objects that has held my interest for so long.
Edited by Rustler46, 02 May 2018 - 01:46 AM.