

Log, May 23, 2008

Finally, finally, finally we have a clear Friday night with no Moon until near closing. Francine and Les were there early setting up and planning out the night. We very much wanted to see Omega Centauri, the object that for several centuries has been classified as a globular cluster ? one of those globes (hence globular) of star balls that circle our own galaxy - the Milky Way Galaxy (MWG). I won't go into details but Omega Centauri has always been an oddball. Large globular clusters [LGCs] have 100,000 to 200,000 or possibly a quarter million stars in them. Omega Centauri has at least 8 and probably 10 million stars in it. LGCs, spin slowly and are not thought to harbor a central black hole, they have very similar stars all about the same age and of similar color because the LGCs form from a single gas cloud and they consume all the gas in a one time period of star building. Simply put, every one of these characteristics does not apply to Omega Centauri.

What Omega Centauri must closely resembles is the core of a small ? possibly a dwarf spiral galaxy. Yet how could it be a small galaxy inside our own galaxy and if it was, where are the whirling arms that are the signature feature of spiral galaxies? So Omega Centauri was classified as a large unusual globular cluster. Recently this has all but been overturned with several startling discoveries. Throughout the region of the MWG called the constellation Virgo are stars which have a slightly different chemical mixture than run of the mill MWG stars. Not really all that weird but somewhat different. Well the upshot of it is that the stars in Virgo appear to be the missing arms of a galaxy which is not our own - and the core of that galaxy is - you guessed it Omega Centauri. Centaurus and Virgo are adjacent constellations with only the tip of the tale of the sea monster (Hydra) between them.

What appears to have happened is that this small galaxy tried to take a short cut through space right past the MWG's core. Not a good place to go if you are a small galaxy and the shortcut is part of one of the two largest galaxies in this part of the universe. The far greater gravity of the MWG simply ripped the arms off the dwarf galaxy. Only the core of the dwarf was densely packed enough that its internal gravity was locally stronger than the distant core of the MWG.

Now it just so happens that the center of Omega Centauri is at 47.5 degrees south latitude. At some time during the year, anything north of 48.7 degrees south latitude becomes visible under perfect conditions along the shoreline of Rhode Island. Even the short distance to Providence is enough that Omega will never actually clear the horizon (although the top of the core just peeks above the horizon). In Boston, not even that peek is possible.

So to make a short story very long and tedious, Francine held the fort while Les set up a remote station on East Beach to see if we could spot Omega Centauri. It was going to reach its highest point (1.2 degrees above the horizon) at 10:03 PM last night. I took down my large astronomical binoculars, a rich field telescope and even my prized Questar 3.5 scope. The sky was clear from the zenith all the way to the horizon, but - But -BUT !!! the moisture above the Atlantic was dense enough that stars could not shine through the damp at any point below 2 degrees of elevation. And therein lies the tale - Omega Centauri came up but could not be seen.

It wouldn't have been so bad, except that people decided not to wait for my phone call to Francine saying I could see Omega Centauri, but came down on speculation. Well I didn't have anything to show them. And then more and more people came down. Oh dear.

Back at the Dome, Francine was having a better time of it. Saturn was glorious. Repeatedly, we went back to look at it. Details which I have not seen in at least 15 months were clearly visible. A real jewel. We tried other things but single handed running of the scope meant we don't have a list of finds for you.

-Les Coleman

Leslie Coleman
Leslie Coleman
Entry Date:
May 23, 2008
Published Under:
Leslie Coleman's Log
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