Pluto and Pal 8

[Ivan Maly]

Last night I managed to get three hours of dark-sky observing under good summer conditions in Cherry Springs. Rare excellent seeing was wasted on a slight problem I was having with the primary cell of my 16”, but I still enjoyed a very decent transparency (for summer, that is – dewpoint was 18 C) and a horizon remarkably free of haze.

A highlight was Pluto just past conjunction with Palomar 8. The globular showed diffuse edges and very little concentration. Unsurprisingly, it was unresolved but had a few stars superimposed on it in the rich Sagittarius field. In the sketch, Pluto is indicated with two dashes SW of the globular. It was slightly brighter than the four immediately neighboring stars, and lay on a side of a tetragon which they formed inside a “hook” of the Z-shaped bright asterism SW of Pal 8. Even a couple days past true conjunction the planet and the globular shared the central area of the field of the Ethos at 225x. UT 2013-07-17 06:00.

753

[Marko]

Good catch Ivan. That would be a fun combination. I could not help but think that the stars in my observation in an 18" of Pal 8 had to be foreground stars as you mention. I had written the following for 278x:

1/10-1/8fov [1.9'] apparent size. Slightly irregular and not completely round. Easy to detect and stands out from background stars. Sugary fine blanket of stars. Grainy texture and perhaps 5 resolvable stars which may be foreground stars of course. Very easy to detect. Stands out nicely with easy stars near it to locate it. Simpler as far as the Pal globulars go.

[Ivan Maly]

That is a fine description, Mark. I regret the lapse of reason that prevented me from correcting the primary pinching problem I discovered when setting up around midnight; given the good seeing I too should have been able to see a little texture across this globular. Such as it was even Pluto was slightly "non-stellar", what a shame.

[Marko]

This is a bit off topic but relates to globulars so please forgive the segway ... When doing the Astronomical League Globular Cluster Club I was trying to see if I could find a system to better judge concentration class for globular clusters. In the end after my analysis I found that there was only a loose correlation in the method I felt may yield nice visual determination of concentration class but I feel I now recognize certain flawed measurement techniques I used and may try again.

If you like globular clusters the Astronomical League Globular Cluster program is a nice way to focus on globs and it force one to really think about globs and how to judge them. The pals of course are an exception in that often there is very little to see with Pal 8 and a few others in that list maybe the better of the batch ranging to Pal 15 as close to insane challenge.


My full submission in spreadsheet form is here in case you are curious: http://www.astrospotter.com/AlGlobClub_MarkJohnston.xls
What is different about these observations is that each glob of fair size and magnitude was being used for my study so you see 3 'measurement' for each which are 1) fully covered central area, mid-glob 50% coverage size and fully detectable size. If I did all 3 of these in exact same eyepiece I think my 'study' may have yielded an interesting and semi-repeatable way to judge globular concentration class.

www.astrospotter.com is my rather crude site that brings together my visual work along with assorted references I have enjoyed.

[Preston Pendergraft]

I pretty much agree with Mark when it comes to observing globular clusters for the observing pin, that having the same eyepiece which is required if I recall. However conditions can change from night to night so having the same power in the scope for each object is really just one easily controllable variable.

For example I observed G1 several times, and only had one night that was really ideal for spotting the little cluster with my scope. Obviously with a larger (or smaller) scope the conditions needed could be different.

[Marko]

At GSSP two weeks back I was tracking down more globs in M31 and for that I like high contrast and fairly high mag but not insane mag. I hope to finish 5-10 more this season in M31 which is about as deep as I want to try with my 18" scope. The 6mm Delos for 282x was ideal for those very tiny, often stellar like globs. I had used G1 (the 'monster' M31 glob) and Pal 6 as a couple of my challenge objects on the AL Glob Club pin but did not attempt my 'science experiment' on those two.

My comments about rating globular concentration class mostly relate to globs that are associated with our galaxy and generally as large or larger than M72 range to have a sporting chance to estimate the 3 parameters.

[FaithJ]

I did the AL Globular program and I agree it was an excellent way of getting to know globular clusters. The concentration class for each one was a headache, some I got spot on, others pretty close and some a bit wide of the mark but, overall, it was a good program which I finished off at TSP last year when I could observe GCs which are too low to get from my home at 50°N.
You don't have to use the same eyepiece or the same scope (I checked with the program co-ordinator) although you should use the closest magnifications possible.
For the challenge object I used NGC 5053 (which is pretty faint and needs good transparency to see well, or even see at all) and I also included Palomar 11.

[Marko]

Faith: The 3rd of my challange objects was Ngc5053 as well. What a dim but fine blanket of stars that one was. We are now in the season where Globulars abound down in and around Sagittarius and I often like to go from lower SAG M55 weaving my way through the lower 'teapot' then up the spout with a quick diversion to M63, M19, 6293 M4 then back round to M28 and M22/6842 combo then divert up north to finish on M14,10,12 as they are so rich.