Regular Meeting: This month's meeting will be on Friday, June 2, in room 215 of the Aerospace Engineering building at 8:00 PM.  Montgomery area car poolers, meet at my house (518 Seminole Drive).  We’ll head for Auburn at 7:00 PM.  Among the items to be discussed will be the AAS shirts.

Star Party: The Tuskegee site has a "No Vehicles Beyond This Point" sign at the entrance to the kudzu field now. Scott Thompson has made arrangements for us to have access to the Russell Amphitheater on Lake Martin. We'll have our June star party there beginning at sunset on Saturday, June 3.

Directions: This site is 2.0 miles north on ALA 63 from the Holley/Hart Field turn off. Turn right on Elmore County 382 (near mile marker 13) at the Piney Woods Restaurant. Go one block to the top of the little hill, and turn left, then bear left at the fork just past the Church. Go about a quarter of a mile and you will see a big green grassy hill on the left. Here's a map of the area:

Our newest member, John Clifton johnLclifton@mindspring.com , an Auburn Graduate student, is currently working on his Ph.D. in Clinical Psychology and enjoys SCUBA diving. He's the proud owner of an 8-inch Meade LX200. Get to know John better on his bio on the "Who R We" page.

Nigel Hornsby hornsbyn@mindspring.comof Franklin AL , has recently sold his Meade 12.5-inch Dob to his brother, but remains interested in astronomy. We found Nigel via his for sale ad in Montgomery's Bulletin Board. Nigel made a couple of suggestions for dark-sky sites that we'll follow-up on.

Richard Brideau brideau@darwinmail.net of Montgomery writes:

Brent Holman holman1@charter.net of Alexander City, attended last month's meeting as the guest of Scott Thompson. Brent has a 10-inch Odyssey Dobsonian. See his bio on the "Who R We" page.

Former AAS member, David Weir dweir@cegi.net writes:

As you recall from the May meeting, Scott Thompson announced that he and Ricky Wood had split the set-up fee for the embroidery work, and already have their AAS shirts. Since we had discussed the club picking up the tab for this, I asked Rhon at the end of the meeting about reimbursing Ricky and Scott. if that OK with everyone. AAS Treasurer, John Zachry, reported $1000.00+ in the treasury. I can't think of a better way to spend our money. I think the shirts will add to the sense of unity and belonging.

Q. What are the available sizes & colors?

A. There are all kinds of sizes and colors, and many different types of shirts. As far as that goes you can go out and buy a shirt that you like!

Q. I think you mentioned some shrinkage -- should we order a size larger than usual, or are the shirts cut big?

A. The Jerzee's pique shirts shrink and I always get a size larger because after three or four washings and dryings shrinks this shirt. The hot dryer usually does the shrinking.

Q. What about caps with the logo?

A. $10.00 plus the cost of the hat.

The cost is estimated to be about $20.00.  An exact price will be quoted later.  Other issues are:

• Could we save money by ordering 20 or so and have them for sale at the meetings?
• Should this be a privilege of membership or for sale to anybody with $20.00? 
• What about $25.00 or $30.00 for non-members as a fund raiser? 
• Should there be an "official" color in addition to member preferences?

Eddie Kirkland, Dorn Majure, his son Trey, Emily Carter and your editor met at the Tuskegee National Forest site. Eddie was trying out his new 5-inch refractor and I had the C-11. We began the evening with a tour of the two-day-old Moon followed by the most of the spring Messier objects and concluding with Omega Centauri and NGC 5128, the "Hamburger" galaxy.

The kudzu has awakened from its winter slumber and threatens to take over the field. Mosquitoes were a nuisance most of the evening. The field now has a "No Vehicles Beyond This Point" sign at the entrance. The search for a better site goes on.

Dr. David King is offering a course called Lunar and Planetary Geology in the coming fall Semester:

LUNAR AND PLANETARY GEOLOGY
GEOL - 3060
Fall 2000
3 semester hours
4:00-4:50 MW; LAB-TBA
118 Petrie
Instructor: D.T. King, Jr. kingdat@auburn.edu
Synopsis: Geological history of planets and satellites of our solar system.
Caveats:

1. Not open to students with credit in GEOL-0106 (Geology of the Solar System).
2. Not open to students without credit in GEOL-0110 or equivalent introductory physical geology (see instructor for consent).*
3. Cannot count as an approved geology elective for geology or earth-science majors (i.e., this is a free elective class only).

* David is willing to waive the prerequisite of Physical Geology if the student will contact him.

David T. King, Jr., Professor, Dept. of Geology
Auburn University, Auburn, AL 36849-5305 USA
kingdat@mail.auburn.edu
VOICE 334 844-4882, -4282 FAX 334 844-4486

This summer, June 25-30, Rainwater Observatory in French Camp, MS is hosting a week long course for astronomy educators. (Teachers or anyone who works with people explaining astronomy) The course will consist of morning sessions on Topics in Modern Astronomy, afternoon sessions doing hands-on Activities in astronomy, and evening sessions with guest speakers on Sky Lore, Astrophotography, etc. Observing through the observatory's telescopes (including the 32") will also be part of the plan.

The course is offered through the University of Mississippi for 3 semester hours undergraduate or graduate credit. To get registration information check the link to Univ. of Miss. Summer School on our web site below or contact us for more information. We'll be happy to send you a flyer.

James G. Hill, Director
Rainwater Observatory & Planetarium
1 Fine Pl.
French Camp, Mississippi 39745
Phone: (662) 547-6865
Web Site: http://rainwater.astronomers.org
E-Mail: jhill@astronomers.org
 
 

Omega Centauri is one of the best globular clusters in the sky. It is the brightest, at 4^th magnitude, and is easy to find with the aid of the Pointers to the Southern Cross - begin with Alpha Centauri, move to Beta Centauri, but rather than continuing on to the Southern Cross, turn north to Epsilon Centauri, and then move a similar distance to a 4^th magnitude "fuzzy" star - and you have arrived at Omega Centauri. Although many observers have a preference for another globular cluster, 47 Tucanae, Omega Centauri is high up on the list of must-see objects - and perhaps, just perhaps, is now worth observing even more for an entirely different reason.

Globular Clusters

Globular clusters are isolated cities of stars. Many tens of thousands of stars are aggregated together in a spherical grouping, gravitationally bound in a volume up to a few hundred light years in diameter. In the Milky Way, the distribution of globular clusters is concentrated around the galactic center i.e. in the constellations of Sagittarius, Scorpius, and Ophiuchus. These three constellations account for about half of the known Milky Way globulars. Indeed, the overwhelming majority of globular clusters are to be found in the hemisphere centered on Sagittarius, whereas only ~10% are found on the opposite side of Earth. This observation was used by Harlow Shapley in 1917 to determine that the galactic center lies at a significant distance from us, and not nearby as previously thought.

Measurements of globular clusters show that they move in very eccentric elliptical orbits which take them well outside the Milky Way disk. The orbits form a halo that reaches out to several hundred thousand light years, far beyond the Milky Way itself, and even the Magellanic Clouds.

By studying the spectra of stars, we can determine the chemical composition of the source of the light. Such spectroscopic studies of globular clusters show that they are much lower in the amount of heavy elements (metals) than stars such as the Sun that formed in the disk of galaxies. This tells us that globular clusters are very old. Why? Globular clusters consist of stars which have formed from the material present when the galaxy was just forming (or even perhaps before its formation). Stars in the disk, on the other hand, have seen the benefit of many cycles of stellar evolution in their neighborhood, with supernovae expelling the heavy elements to be used later in new star-forming areas.

It’s worth noting that the globular clusters we see today are the survivors of what would presumably have been a larger population of globulars in the early years of the Milky Way - the unlucky ones having been disrupted as they moved through the Galactic disk, thus spreading their stars throughout the Galactic halo.

Omega Centauri

Being as bright as 4^th magnitude, the location of Omega Centauri (also known as NGC 5139) has been known since ancient times. It was listed in Ptolemy’s catalogue as a star, and received its "Omega" designation from Beyer in his catalogue of stars. Edmund Halley (of Halley’s Comet fame) was the first to document its non-stellar appearance, listing it as a "luminous spot or patch in Centaurus".

Sir John Herschel wrote : "The noble globular cluster Omega Centauri is beyond all comparison the richest and largest object of its kind in the heavens. The stars are literally innumerable, and as their total light affects the eye hardly more than a star of 4^th magnitude, the minuteness of each star may be imagined".

In the recent edition of Hartung, Omega Centauri is described as :

"...Its myriad stars are broadly compressed towards the center. It is powdered with faint stars with 7.5cm [aperture], and with 10.5cm looks like delicate tangled threads of beaded gossamer. Larger apertures show a pronounced lace-like pattern which seems to be made of small crossing curved lines of stars. Dark lanes and streaks are evident with moderate magnification and the star distribution is far from uniform. On a clear night it is a most impressive and beautiful sight."

New Research

At a recent conference on the Galactic Halo, astronomers from the University of Virginia and from the Carnegie Institution’s Las Campanas Observatory presented findings in which they claimed that Omega Centauri, a globular cluster dear to our hearts, may in fact be the core remains of a formerly larger dwarf galaxy that has undergone considerable stripping by the Milky Way’s tidal forces!

Wanna run that one by me again?

Let’s take a closer look at the features of Omega Centauri, as outlined in the paper.

Mass And Shape : Omega Centauri is big, very big. It is the most massive of the globular clusters in the Milky Way, and its flatness also distinguishes it from other globulars. The only other globular cluster in the Local Group of Galaxies that is more luminous than Omega Centauri is the globular G1, a part of the Andromeda Galaxy (M31).

Abundance : Omega Centauri’s chemical abundances have long been known to be unusual for a globular cluster. The wide spread in the globular’s metallicity distribution function, according to the astronomers, suggests a complex formation process.

Age : An independent paper presented at the conference claimed that there was an age spread of 4 billion years in the stars within Omega Centauri. One would not expect star-forming to be occurring at such different times in a normal globular cluster.

Orbit : Omega Centauri’s orbit around the Milky Way is unusual. It is strongly retrograde, and is somewhat confined to the Galactic plane.

To account for these unusual characteristics, the astronomers suggest that Omega Centauri may have originated in, or as, a satellite galaxy of the Milky Way. They go on to further postulate that Omega Centauri itself may be the surviving nucleus of such a satellite galaxy, and that the chemical abundances, age, and orbital parameters of Omega Centauri match such a scenario.

This in itself is not a new idea. In 1991, Raymond White, of the University of Arizona, suggested in a popular article that Omega Centauri’s obvious ellipticity, combined with its chemical abundances, could be seen as suggesting a possible origin as a dwarf galaxy. White noted that dwarf ellipticals such as Sculptor, Fornax, Ursa Major, and Leo II were all metal poor and showed features in their color-magnitude diagrams that were shared by Omega Centauri.

The idea (which isn’t the sole possible explanation for Omega Centauri’s unusual features) gains further interest when we consider that the globular cluster M54, discovered by Charles Messier in 1778, was found a few years ago to be not part of the Milky Way, but instead part of the Sagittarius Dwarf Elliptical Galaxy (SagDEG), which itself was only discovered this decade (thus, Messier has the credit of being the first to discover an extragalactic globular cluster). At least one team of astronomers have suggested that M54 may itself be the nucleus of SagDEG. This galaxy is the closest to the Milky Way and is currently being tidally disrupted by the Milky Way.

During Summer, Omega Centauri is admittedly only best observed during the hours before dawn. However, as the year progresses, Omega Centauri will become better placed at an earlier hour. It’s well worth revisiting this delight of the Southern sky - one whose nature might not necessarily be what you may have thought.
 

Hoping to see everyone at the meeting,

Russell