AAQ Visual Observing Section

Selected Deep Sky Objects In Sagittarius

As well as checking out some more double stars this month, I thought we should take a look toward the very centre of our own Milky Way galaxy. Found in abundance here are some of my favourite deep sky objects – globular clusters. Listed below are just a few easily found ones to whet your appetite. All observations were made through a 150mm f/8 refractor.

M 22 (18h 36.4m RA, -23° 54' Dec) Set amongst a pretty background star field is this beautiful globular cluster, with many individual stars clearly visible even @ 40x.

M 28 (18h 24.5m RA, -24° 52' Dec) Now contrast this smaller cluster with M22. It can be clearly seen with 80x, but 120x is needed to just resolve individual stars.

NGC 6638 (18h 30.9m RA, -25° 30' Dec) Even smaller again is this cluster, where I was unable to see any individual stars. The nearby planetary nebulae NGC 6644 and PK7-6.2 were unseen through my telescope – give them a try and see if you are successful.

M 54 (18h 55.1m RA, -30° 29' Dec) This easily found small tightly condensed cluster has a very bright core, but 120x was unable to resolve individual stars.

M 69 & NGC 6652 (18h 31.4m RA, -32° 21' Dec & 18h 35.8m RA, -32° 59' Dec) Both these clusters will just fit in to the same field of view with a wide field eyepiece. M69 is the brighter of the two, with a few stars visible at 120x.

M 70 (18h 43.2m RA, -32° 18' Dec) Easily found, but no discernable individual stars in this globular cluster.

NGC 6624 (18h 23.7m RA, -30° 22' Dec) A small globular cluster with a bright core at 40x, but again no stars seen at 120x.

NGC 6569 & NGC 6558 (18h 13.6m RA, -31° 50' Dec & 18h 10.3m RA, -31° 46' Dec) For a good test, try locating these two globular clusters. They are not easy to find, very faint with no discernable stars seen. As with the previously mentioned planetary nebulae, I was unable to glimpse the two close by - PK1-6.1 and PK1-6.2

Lambda Sagittarii (18h 28.0m RA, -25° 25' Dec) Two pair of doubles are nearby (Burnham 133?), both of similar magnitude and separation. They are clearly visible at 40x, forming a triangle of brighter stars against a lovely background star field. They make a good contrast with another pair on the opposite side of Lambda, which required 160x to separate.

Burnham 245 (18h 10.1m RA, -30° 44' Dec) Located near Gamma Sagittarii you will find this beautiful pair, with a strong orange/red primary, easily split with 120x. Again, a pretty sight amongst the background stars.

Herschel 5003 (17h 59.1m RA, -30° 15' Dec) Found on the opposite side of Gamma Sagittarii, and near globular cluster NGC 6522 is another double clearly seen with 120x. This is an attractive combination of yellow primary and blue/green secondary.

21 Sagittarii (18h 25.3m RA, -30° 32' Dec) For a real test try this double out, at 2.0” separation I had great difficulty splitting it even at 320x, although seeing conditions were below average for this particular observation.

While admiring the Lagoon Nebula (M 8 18h 03.8m RA, -24° 23' Dec) and Triffid Nebula (M 20 18h 02.6m RA, -23° 02' Dec), check out the easy doubles (80x) visible in each. Take your time in this constellation, as you will be well rewarded for a few nights viewing with the rich array of open and globular clusters, nebulae and double stars to be found.

I use “Hartung’s Astronomical Objects for Southern Telescopes” as an excellent source of information on objects visible to the amateur scope. If you don’t have a copy for your own use, the AAQ library has one available, or it can usually be found for sale at the various telescope retailers.

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