Archive for May, 2007

17 05 2007

Red-Shift Based Distances to NGC 6166 & 4889

Posted by: Dick_Hodgson in Dicks Observations

Subject: Red-Shift Based Distances to NGC 6166 & 4889Hi again guys,

Thanks for the warm responses to my report of last night’s observing of NGC 6166. It is always a joy to hear from you. Thanks also, JJ, for the links you supplied regarding distance information.

I have looked at them carefully. While red-shift based distances to remote galaxies may be slightly affected by local gravitational perturbations of near-by galaxies, and the movement of local galaxy clusters around their respective superclusters, I do think the rate of recession of galaxies (as part of the expansion of the Universe) does give us their approximate distance from us. Based on the current Wikipedia value for the Hubble  Constant of 71 +/- 4 km/sec/Megaparsec distance, which is probably very close to the truth on this subject, approximate distances may be worked out.
 
Working Out NGC’s Approximate Distance:  Parsec distances, long used in stellar astronomy, can be converted to light years by multiplying by 3.2616 — thus, given NGC 6166′s red shift of 9,100 km/sec, and using the 71 km/sec/Mpc value for the Hubble Constant  (the expansion rate of the Universe), gives us an approximate distance of 418,036,040 light years. This is hyper-precise given the uncertainties. I think it would be best to round it off to ~ 420 million light years. That would probably be close to the  truth, give or take 20 or 30 million, and fits most of the other data we have at present. One week ago, as I previously mentioned, we located NGC 4889, the brightest galaxy of the 1,000+ galaxies known in the Coma (Berenices) Galaxy Supercluster. Its red shift according to the Nasa/Pac Extragalactic Database, is 6,495 km/sec, and thus suggests a distance of 298,367,490 light years, which should be rounded off to ~ 300,000,000 light years.

These are genuinely astronomical numbers. Do they matter?  I think they do if we bring them down to our planet Earth’s history and prehistory. We want to inspire the parents and their kids who come to our open-house observing sessions. How better to do this than to ask, when looking at Sirius the Dog Star, what they were doing 8.8 years ago when that light started toward us. Looking at Betelgeuse, think of what Columbus was doing when its light began the voyage. Etc.

 Three hundred million years ago, when the light from NGC 4889 began toward us, Earth was in the late Pennsylvanian Period. It was a time when the earliest reptiles stalked the land, and the great “Coal Age” was drawing to a close. The old Atlantic Ocean was being destroyed by plate tectonics as globally continents would soon collide to form the supercontinent Pangaea, and the

Appalachian Mountains, tall as today’s

Himalayas, would arise as the result. The earliest dinosaurs were sixty million years into the future. Do you suppose any creatures in the Coma Supercluster’s NGC 4889 have been looking at us as we now look at them?
Four hundred twenty million years ago, if that is when NGC 6166′s light began its journey to us, Earth was in the late Silurian Period. In Earth’s oceans the earliest jawed fish with armor were the new arrivals, and on land the first vascular plants, rootless and without leaves, appeared. Mosses, ferns, trees and grasses were yet to come.

Those were both long times ago. None of us can grasp how long ago that all was, or how far the light of supergalaxies NGC 4889 and NGC 6166 has come to us. But we can look at the “fossilized light” that comes to us with our telescopes!

So let’s go out, observe, inspire people to look up, and consider the Universe of which we are citizens! Thanks again guys for your help and encouragement!

 Dick

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17 05 2007

Super-galaxy NCG 6166 in Hercules Observed!

Posted by: Dick_Hodgson in Dicks Observations

Subject: Super-galaxy NCG 6166 in Hercules Observed!

Hi Guys,

Tonight (2007 May 16-17) was clear and calm, so I returned to our Observatory to try again the see NGC 6166, the brightest galaxy in the remote Hercules Galaxy Supercluster, with our 635mm (25-inch) Obsession telescope. The Argo Navis was continuing to track well from its January alignment. After brief views of Spica, Alphecca (Alpha CrB), and magnificent views of M13, the Great Globular Cluster in Hercules  — a mere 22,000 light years away I awaited total darkness.

At (May 17 UT, = May 16 CDT) I dialed up NGC 6166, and armed with the map of the target John Johnson had so kindly e-mailed me a few hours before, the examination of the sky began. It was hard to know the scale of the map, and the orientation. There were no really bright stars in the field of view, mostly 10th magnitude and fainter. Nothing seemed to match up. Things that might possibly have been galaxies, upon high power inspection, were not. I had been listening to a CD of Beethoven’s magnificent 9th Symphony, and pretty much decided to quit when the choir did, when I decided to try one more time. Suddenly I spied a faint “fuzzy,” centered it in the field of view. It was ( local time). Immediately I knew it was a galaxy, but which one?  I began checking star patterns against the map, and after a few minutes found a perfect match once I had figured out the scale!  It was thrilling. The 9th Symphony was coming to its climax, and I examined NGC 6166 for a few minutes 85x and 201x. Once I saw it, it was easy to see, and was brighter than expected  — the use of averted vision was not necessary although I had had no Observatory lights on for some time, so I was fairly well dark adapted.

By the way, I am rechecking the distance quote I gave earlier today. It was based in part on Kepple & Sanner, but they use 50km/sec/Megaparsec for the Hubble Constant, and we now have good evidence that it is close to 71km/sec/Mpc, so that affects distances largely based on red shift values. I have also been trying to get red shift values based current sources, and you might be surprised how difficult that seems to be. The Hercules Galaxy Supercluster is certainly more remote than the Coma Supercluster (which is 320,000,000 light years based on current data), but how much more?  If any of you can suggest data sources to solve this question, I would be glad to hear from you.

 

This report from Hodgson Observatory filed with you, I’m going to bed. Clear skies to you all,  Dick

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16 05 2007

Quest for Supergalaxy NGC 6166 in Hercules

Posted by: Dick_Hodgson in Dicks Observations

Subject: Quest for Supergalaxy  NGC 6166 in Hercules

Hi Guys,

In recent days as some of you know I have been compiling “Constellation Checklists” for use in deep-sky surveys on my computer. I just finished doing the work on Hercules yesterday morning. I have also been smitten with a “bug” lately to search for the most remote galaxies that can be seen with our larger telescopes. On Friday evening, May 11, when some of us were together I had just completed the Coma Berenices checklist so I decided to make the acquaintance of NGC 4889, a giant elliptical galaxy in the Coma Galaxy Cluster, ~ 300,000,000 light years distant. It is a

Caldwell object, and was a joy to see!

Now I want to go after more distant prey, and I invite those of you with large apertures to join me in the coming weeks on dark, transparent nights. In the great Hercules Galaxy Super cluster, just about 500,000,000 light years distant there are several giant “supergalaxies” worth seeing. The brightest of them, in Abell Cluster 2199, is NGC 6166, a giant elliptical, which is +11.8 in apparent visual magnitude. It is described in Kepple
& Sanner, and is said to require at least 12-inches aperture and very good observing conditions to be seen.

Last night, finding the sky had cleared, I went out at and opened the Observatory. After checking out the Argo Navis / ServoCAT system on Spica, and finding it was still orienting well from its late January alignment (!),  I went to NGC 6166 in Hercules. I think I saw it but the sky transparency was not quite what I would have liked and there were several objects of near-similar brightness, so I can’t be sure. I will get more familiar in the next few days with the faint star field around NCG 6166 from Kepple & Sanner’s book and “The Millennium Star Atlas” of mine – its not far from the great globular cluster M13 — and revisit NGC 6166 soon. It would be a thrill to see light that began heading for Earth at the close of our Cambrian Period, the time of the great trilobites, when all life was in the sea!

So guys (& gals) I put it up to those of you with the larger equipment – or intrepid observers who want to use mine – are you up for hunting for NGC 6166 too?  I think the challenge would be fun!  I hope to do so in the coming days myself.

Cheers,  Dick

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