Hi All,
It has been a little while since I posted here but most of the (relatively) few observations I've made in the last 6 months (due to cruddy weather) have been done for the purposes of publication elsewhere so I've had to withhold them.
Last Saturday night was a goodish night at the Southern Highlands site we use near Bargo. Not particularly dark but the seeing was pretty good -- I'd rate it 7/10 with a nice crisp image of Saturn earlier in the evening at x247. The SQM-L reading around midnight was a bit better than 21.0. I observed a whole heap of galaxies in Pavo and then Tucana later in the evening after some high cloud stopped us from serious observing until about 9pm. I won't bore you with all of them but I though I'd post here one observation of an object I know is a favourite of SAB (PGC) -- he made a post about it here a couple of years ago now -- AGCS 805. I enjoyed this cluster of galaxies for about 25 minutes and decided to write an entry about it for the Sydney Observatory blog that I hope will be published in the next few days.
Here is a copy of the blog note I have submitted that some might find interesting and below that are the observations:
Big picture part of an even bigger picture
Galaxies, like stars, have a tendency to live in clusters. I came upon this cluster of galaxies —Abell Galaxy Cluster South (AGCS) 805 while observing last weekend in the Southern Highlands. As I viewed it for almost a half-hour and identified nine of its galaxies, I was struck not only by their beauty, but also by how they fitted into the larger picture of the Universe.
We see AGCS 805 through a scattering of stars that make up the constellation of Pavo (The Peacock) in our southern sky. These stars (like the Sun) are in our Milky Way Galaxy and “only” 10s to 100s of light years away — one light-year is about 9.5 trillion kilometres. AGCS 805 includes at least eight major galaxies and probably several dozen dwarf galaxies. In this flat “2-D” photograph, all the galaxies seem to be equally distant from us. Most here are true members of AGCS 805 about 220 million light-years away. However a few are several tens of millions of light-years in the foreground while a few others are about twice as far away in the background. The brightest galaxy in the centre of the image is IC 4765 — a 12th magnitude supergiant elliptical galaxy that gravitationally dominates the lesser cluster members.
Adding an extra dimension to this big picture, because AGCS 805 is about 220 million light-years distant, we cannot see these galaxies in “real time”. We can only see them as they were 220 million years ago because it takes that long for their light to reach our telescopes. The light from these galaxies we see now left them about the same time the first true dinosaurs roamed the Earth in the mid-Triassic period.
The image is 1/3 of a degree across or about 2/3rds the apparent diameter of the Moon in our sky. It is also the same size as the view in a 9mm eyepiece in my 18” Newtonian at x247 magnification. At 220 million light-years distance, this image (and my eyepiece field) measures about 1.3 million light-years across.
AGCS 805 is a massive cluster of dozens of galaxies containing trillions of stars (so vast and remote as to be beyond meaningful human comprehension). However, it is just one component of a vastly bigger panorama — in the same way a masonry block is part of a wall or building. AGCS 805 is part of the gargantuan Pavo-Indus super-cluster of galaxies including more than a dozen other similar galaxy clusters — a cluster of galaxy clusters. The Pavo-Indus super-cluster contains well over a thousand galaxies. These super-clusters, chains and walls of galaxies that can stretch up to 500 million light-years are the largest structures in the visible Universe.
* * *
Here is a link to an image:
http://stdatu.stsci.edu/cgi-bin/dss_...e&fov=NONE&v3=
Below are the observations 12mm TII Nagler at x185 and 9mm Nagler at x247
IC 4765 Galaxy *
RA: 18h 47m 17.8s Dec: -63° 19' 52"
Mag: 12.3 (P) S.B.: --- B-V: --- Size: 3.4'x1.8' Class: E+4
P.A.: 115 Inclination: --- R.V.: +4669 Source: RC3 *
ESO 104-7 PGC 62408 Galaxy *
RA: 18h 47m 18.3s Dec: -63° 21' 32"
Mag: 12.9 (V) S.B.: --- B-V: +1.05 Size: 1.6'x0.8' Class: E?
P.A.: 97 Inclination: --- R.V.: +3899 Source: RC3 *
PGC 62391 Galaxy *
RA: 18h 46m 51.6s Dec: -63° 18' 51"
Mag: --- S.B.: --- B-V: --- Size: 0.4'x0.3' Class:
P.A.: 39 Inclination: --- R.V.: +10795 Source: PGC *
ESO 104-2 PGC 62393 Galaxy *
RA: 18h 46m 53.9s Dec: -63° 21' 39"
Mag: 14.1 (V) S.B.: --- B-V: +1.01 Size: 1.0'x0.3' Class: S0?
P.A.: 30 Inclination: --- R.V.: +4055 Source: RC3 *
ESO 104-8 PGC 62412 Galaxy *
RA: 18h 47m 23.1s Dec: -63° 18' 35"
Mag: 15.6 S.B.: --- B-V: --- Size: 0.9'x0.4' Class: L
P.A.: 153 Inclination: --- R.V.: +4075 Source: PGC *
IC 4766 Galaxy *
RA: 18h 47m 35.6s Dec: -63° 17' 30"
Mag: 13.8 (V) S.B.: --- B-V: +1.04 Size: 1.1'x0.4' Class: SA(r)0+
P.A.: 112 Inclination: --- R.V.: +4998 Source: RC3 *
IC 4770 Galaxy *
RA: 18h 48m 10.4s Dec: -63° 23' 01"
Mag: 15.4 (P) S.B.: --- B-V: --- Size: 0.8'x0.5' Class: (R)SAB(rs)a:
P.A.: 65 Inclination: --- R.V.: +5040 Source: RC3 *
IC 4767 Galaxy *
RA: 18h 47m 41.8s Dec: -63° 24' 20"
Mag: 14.3 (B) S.B.: 13.6 B-V: +0.93 Size: 1.4'x0.4' Class: S0+: pec sp
P.A.: 30 Inclination: --- R.V.: +3600 Source: RC3 *
IC 4764 Galaxy *
RA: 18h 47m 07.9s Dec: -63° 29' 05"
Mag: 14.7 (P) S.B.: --- B-V: --- Size: 1.2'x0.3' Class: S?
P.A.: 128 Inclination: --- R.V.: +3900 Source: RC3 *
These members plus others are part of AGCS 805. The brightest eg and presumed to be the gravitationally dominant cluster member is IC 4765 at centre which is also somewhat the brightest. -65 is a moderately bright eg 1.5 to perhaps approaching 2' diameter, round with weak edges but growing weakly to centre and then within the central 1' broadly and slightly to centre without nucleus.
ESO 104-7 is about 2' S of -65 not quite at a 10th mag * that is directly further S. Small, perhaps 30" diameter of goodish SB and rising moderately to centre.
PGC 62391 is 3' WNW of -65 and is about 20-30" diameter spot of goodish SB, comparable to 104-7 above but perhaps not quite as good.
ESO 104-2 is again similar but perhaps the faintest of these inner central 4 eg. The 4 make a rough square about 3' a side.
ESO 104-8 is 2.5' N of IC 4765 as a small faint spot about 20" diameter brightening a little to centre and
IC 4766 is 3.5' NNE looks similar but a little bigger and brighter and oval in PA 45, 30 x 20".
IC 4767 is an elong or edge on eg of very low SB, very diffuse slash in about PA 45, 1.5' x 10" of consistent very LSB. Diffuse edged. It is 5’ SSE of IC 4765.
IC 4764 is 8' S of -65 and looks similar to -67 save that it is in PA 135 and a fraction smaller -- perhaps 1.25'long.
IC 4770 is 6' SE of -65 and presents as a 40" dia round patch of very weak gossamer with no central brightening. Very, very faint and of very LSB.
Best,
Les D
It's now on the blog:
http://www.sydneyobservatory.com.au/...Observatory%29