1. Chris's Introduction.

Chris welcomed everyone and gave a brief overview of the society. It is important to note that free parking is available from 7-11 at area 5 behind the building. Calendars are now on sale for $15. We also have some odds and ends left over from the GA, such as pins.

2. John Hawkins. An Introduction to Globular Clusters.

John is a graduate student of Dr. John Lewis. Here is a brief summary of the topics of the talk:

Open (Galactic) Clusters.

Consist of Population I stars.
Usually 1-20 parsecs in radius.

Globular Clusters

Usually 100,000 to 1,000,000's of stars. Many more than an open cluster.
Age about the same as the universe.
5-15 parsecs.

Globular clusters are a sort of laboratory for stellar evolution, and the age of the universe.
What is spectral analysis?

Stars emit blackbody radiation.
Absorption lines.
Spectral types.

Distance Measurement.

Parallax or "Standard Candles".
RR Lyrae variable stars.
Sub-dwarfs (but very faint). Some recent work indicates their distance scale could be as much as 10% off.

Hertzsprung-Russell (HR) Diagram.

Car analogy. (Fast, slow, compact, sports car, etc.)
90% are on the main sequence burning Hydrogen to Helium.
HR diagram of a Globular Cluster.

Characteristics of a Globular.

Share age, distance, and chemistry.
Mass is really the one variable.
So, we can have a better experimental comparison with our models of stellar evolution.
Three formation models: before, during, or after host galaxy. Was the cluster pre-enriched or self-enriched with metals?
Destruction?

Dynamics: The King Model.

How to model a Globular.
Some problems:

Eventual equipartition of the energy of the ensemble of particles.
Core collapse.
Tidal forces (from host galaxy) ignored.

Some improvements on the King Model.

Age of the Universe.

Over the last 10 years we believe we have a much better handle on the age of the universe. No longer do we have the embarrassment of the age of some globulars exceeding the predicted age of the universe.
Globular Cluster age determination.
Age of M4 cluster (about 12-13 billion years).

3. Observations.

Chris: Sun. Aurora.
Randy: Aurora.
Florence: Green Aurora from vehicle on Foxtrap Highway.
The lunar eclipse was clouded out. This was Garry Dymond's fault.

4. What's Coming Up. Robert Babb.

Planets are mostly morning objects except Saturn (and Uranus/Neptune). Leonids are this week. Geminids on December 15. Occultation on December 7. A possible good comet may be C/2004 Q2 (Machholz) later on.

5. Christmas Shopping. Randy Dodge. Gary Case.

Randy noted a good deal on the Celestron Nexstar 80GTL can be had at Costco. These go for $285 at Costco, but "non-L" version typically goes for $449 or more on the mainland. For a slightly better scope, you are saving over $150. There are also Bushnell 10x40's. If you are interested in binoculars the Birdshop has offerings as well.

Gary went to the Geocentre and Chapters. The Geocentre has a number of astronomical gifts, mainly for the younger set. Chapters has some of the best range he has seen in a long while. Gary has a detailed list which he passed out.

6. Coffee.

Other Minutes: All Previous Next

Please send any additions or corrections to:

David Bourgeois

This document was generated using AFT v5.095 and Vim on: Sun Nov 21 22:37:28 NST 2004