Sky Sketcher's Post Mortem 1

SKY SKETCHERS POST MORTEM

By Scott Mellish

HICKSON 16

GALAXY GROUP CETUS R.A. 02 09 24.7 -10 08 10

A Hickson Compact Group or HCG for short is a collection of galaxies catalogued by Paul Hickson in 1982. One of the most famous of these groups on Hickson’s list of 100 objects is HCG 92, Stephan's Quintet. However the group discussed here in this Post Mortem is HCG 16, a nice collection of four NGC galaxies in the constellation of Cetus. This was a splendid collection of four NGC galaxies in the 56cm dob at 314x magnification, and while they were not bright they were very conspicuous in the 15' field as seen in the sketch.

An observing report by Steve Gottlieb on NGC 835 one of the members of this group (which is the second object from the bottom of the sketch) appears below-

"NGC 0835 = MCG -02-06-031 = Arp 318 = HCG 16a = PGC 08228

02 09 24.6 -10 08 10

V = 12.1; Size 1.3x1.0; SB = 12.3; PA = 80d

17.5": moderately bright, small, round, bright core. Brightest of four in the HCG 16 group and forms a close pair with N833 1.0' W. N838 lies 3.4' E and N839 5.3' SE. A mag 10 star lies 2.7' S."

From top to bottom in the sketch field is- NGC 838-838-835 and 833, all of which are very similar in appearance. Deep images of this group show faint trails of gas and dust between the galaxies as they interact with each other.

NGC 7293 THE "HELIX NEBULA

"PLANETARY NEBULA AQUARIUS: 22 29 38.5 -20 50 1

NGC 7293 or also known as The Helix is a large planetary nebula in the constellation of Aquarius. Discovered by Karl Ludwig Harding around 1824. The Helix is one of the closest of all the bright planetary nebulae. The estimated distance is about 700 light-years, it is somewhat similar to the Ring Nebula in Lyra. This was the first time that I had observed the Helix in my 56cm f5 dob, and the view was most impressive. The combination of a 17mm Nagler and a 2inch Oxy III filter made the nebula dominate the 29' field. I was surprised at how bright the central nebulosity was in comparison to the main outer ring, which is not something that I recall noticing much in my old 41cm dob.Another observing report by Steve Gottlieb is as follows -

"NGC 7293 = PK 36-57.1 = Helical or Helix Nebula = PN G036.1-57.1

22 29 38.5 -20 50 13

V = 7.6; Size 880"x720"

17.5" (10/2/99): gorgeous view at 100x and OIII filter. This huge, annular PN is 15'x12' in size and slightly elongated E-W due to an extension on the W side. The thick annulus is mottled and irregular with brighter regions along the N, NE and SW edge. The W side is slightly weaker but very faint extensions from the N and S side towards the W, cause the rim to bulge on this side. The west edge of the halo more gradually blends into the background near a mag 11.5 star off the W side. At 220x without a filter about a dozen stars are superimposed. The mag 13.5 star is easy along with a similar star a couple of arcmin following."

PALOMAR 8

GLOBULAR CLUSTER SAGITTARIUS: 18 41 29.9 -19 49 33

The fascinating list of 15 Palomar globular clusters was discovered in the 1950s on the plates from the original Palomar Observatory Sky Survey. Numerous notable astronomers of the day were involved in determining them as globular clusters, such notables as the likes of Edwin Hubble, Walter Baade, Fritz Zwicky, Halton Arp and George Abell. A number of the clusters are fairly close by and of average size; however they are heavily obscured by dust in our Milky Way galaxy. Others in the list like Palomar 3, Palomar 4, and Palomar 14 are giant globulars but are extremely far away in the outer halo of the Milky Way.

These objects are often considered "Extreme Halo" globulars. Most of the Palomar clusters vary greatly in degree of difficulty ranging from easy to nearly impossible. Observing the list in its entirety is a one of the great observational challenges for amateurs with large dobsonian telescopes.

During the August new moon at Wiruna I thought that while Sagittarius is well placed in the sky I might try for the globular cluster Palomar 8, which at a listed mag of 11.2 was not going to present to great of a challenge in the 56cm dob. In the eyepiece at 354x this rather diffuse globular cluster was partially resolved with just the barest smattering of stars dotting the soft nebulous surface. Some of the stars required averted vision to resolve. The field around this globular was strewn with faint stars, with a few being moderately bright. Palomar 8 is around 6' in size, and a dark sky is an obvious necessity.

Clear skies