Herculean effort 26/09/19

[domstar]

A beautiful night on the balcony.  No chills, stellarium on hand, and the ability to have a break and some night-time cereal. My double star atlas has been mostly a beautiful decoration since Orion disappeared before spring but I did the necessary squinting to research some delightful doubles in Hercules. 

A short time ago when the moon was nearly full, I'd done the same and surprisingly (at least to me) I'd failed on every single one. This time it was easier and more successful. I was surprised to learn Rasalgethi was in Hercules- and alpha no less. I'd always thought it was part of Ophiuchus. I enjoyed that and also about 5 more doubles which were starred in the Cambridge atlas but I can only read in bright sunshine. I gave Zeta a try but I knew I didn't stand a chance. 

The rest of the evening I looked at the always disappointing Summer Beehive and a few interesting open clusters in Aquila- the Flying Unicorn, Graff's Cluster and the Tweedledum Cluster. Then the little glob in Delphinus- Caldwell 47. However, probably the most enjoyable time was spent staring into space around the area where Barnard's Galaxy should be. I've been on the case 4 or 5 times this year and I have the exact spot but no cigar. The Little Gem is there but not Barnard's. I know I should wait for better transparency but I'd like to ask what eyepiece I should be using. The biggest exit pupil (32mm eyepiece about 3.5mm exit pupil) or a darker background 25mm eyepiece? Neither have worked for me yet.

My other question is about double star exit pupils. Do I understand it correctly that at 1mm and below I get to see the airy disc and above that I don't? Does that mean that for my f9 scope my 9mm has a significant advantage over my 10mm eyepiece despite probably not quite being of such good optical quality?

So all in all I had a lovely time. It's great to get somewhere dark with an all-round view but staying at home with the proverbial pipe and slippers has its place too.

Thanks for reading,

Dominic

Edited September 27, 2019 by domstar
I got the date wrong

[Marvin Jenkins]

Loved it all. Completely understand the comfort side of things. Get out to a dark sky site also. We are all here to look at the stars and although I generally do not do the ‘splitting doubles’ thing, the open nature of the above observation session mirrors my own and feels so natural.

Understanding and questions come hand in hand, knowledge and answers are not always in balance. I learn so much from posts like this, long may it continue.

Marvin

[Littleguy80]

Excellent report, Dom. Barnard’s galaxy is a tough one. I’ve only managed it once and it was more like a faint nebula than a galaxy. From memory, I observed with my 20mm (4.3mm exit pupil) and 13mm (2.8mm exit pupil). I believe the darkened background with the 13mm helped. 

[domstar]

Thanks. Those exit pupils sure are big on fast scopes. I wonder what difference that makes.

[cloudsweeper]

1 hour ago, domstar said:

Thanks. Those exit pupils sure are big on fast scopes. I wonder what difference that makes.

Well Dom, apart from other things, it means the sky brightness is greater so everything looks washed out (poor contrast).  Also light will be wasted since the exit pupil exceeds the eye's pupil.  But these things aren't a problem for wide views of brighter objects!

Doug.

[domstar]

13 minutes ago, cloudsweeper said:

Well Dom, apart from other things, it means the sky brightness is greater so everything looks washed out (poor contrast).  Also light will be wasted since the exit pupil exceeds the eye's pupil.  But these things aren't a problem for wide views of brighter objects!

While you're here, Doug, what about the exit pupil airy disc thing? You have an impressive range of scopes, is the 1mm or less exit pupil something you consider when observing double stars? 

[cloudsweeper]

1 minute ago, domstar said:

While you're here, Doug, what about the exit pupil airy disc thing? You have an impressive range of scopes, is the 1mm or less exit pupil something you consider when observing double stars? 

It's an interesting subject Dom.  The resolution limit corresponds to an exit pupil of say 0.5mm, but that is only a convention.  Also, for splitting stars, there are so many factors coming into play.  Bottom line - I'm happy to go down an exit pupil of about 0.4mm. 

(Hope this helps for now - I'm away from my notes and reference material,  putting up a large bookcase / partition thing at my daughter's - time well spent when clouds and rain prevent any stargazing!)

Doug.