Minimum aperture for splitting 90 Her
Posted 27 October 2012 - 04:06 AM
On the other side there are always these irritating reports of splits of difficult doubles with incredible small apertures.
Did you ever observe 90Her and if yes what aperture did you need to split it or with which aperture did you fail?
Posted 29 October 2012 - 09:27 AM
Posted 29 October 2012 - 07:47 PM
Burnham added this pair to his catalog in 1879 (BU130) using his 6" refractor saying: "The components have a striking difference in color - golden and blue"; a beautiful pair, even with a small aperture." Of course his 6" scope was made by the Clark & Sons!
Posted 30 October 2012 - 02:48 AM
Thanks to VanJan for the observation report. Is light pollution also of relevance for you and what percentagr of diameter is the CO of your Newton?
Posted 30 October 2012 - 10:46 AM
My NELM is about 4.5 mag. I no longer own the Newt, but I believe the CO was 29 percent.
Posted 30 October 2012 - 07:10 PM
PJ's note about SW Burnham is interesting. Though back then, Burnham measured the pair at 1.9", a little easier than now - there has been slow change in this long period binary. No chance of an orbit yet, from the numbers I've seen.
So, despite the RoT suggesting 170mm needed for seeing 90 Her as a double, a bit less aperture might do it IF the seeing is steady enough, and with magnification over 200x.
Posted 30 October 2012 - 08:46 PM
I'd seen this one nicely split some years back at 180x with a 7-inch refractor. This time, even with Theta high overhead, it needed 250x for a neat separation with a 140mm (5.5-inch) refractor. The companion was seen at less power, but not cleanly separated.
90 Her will be tougher. So I'm thinking that separating it with 140mm, if that is possible?, will take very good air steadiness and good visual acuity by the observer. And quite high magnification.
Posted 31 October 2012 - 05:59 AM
Fred, this is certainly true - I think I can see stars up to +11,4mag with averted vision and this means a loss of "only" about 2 magnitudes compared with the theoretical limit of +13,4mag.
... Your telescope loss will be less than the 3 magnitudes of naked-eye loss ...
If I add 2 mags to 90 Her this would give a +7.3/10.8mag double and I assume that the same delta-m gets increasingly difficult with fainter pairs.
I will certainly try again, but have to wait for next year because Hercules has meanwhile left my field of view.
Posted 31 October 2012 - 09:41 AM
Posted 31 October 2012 - 12:30 PM
Posted 02 November 2012 - 02:52 AM