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Location: Chemistry/Physics Building, MUN
Time: 8:00 pm
Present: 18
1. Randy's Introduction. Summer stuff. GA is next week in Vancouver, three members will be attending. Randy showed the concepts for our July 1-4, 2004 GA brochure (not quite finished). Some discussion of National Council issues. Help is wanted for our GA 2004. News on the Universe Centre: according to Fred Smith our application is moving through ACOA at Moncton, and we have sent in our business plan. In short, things look good.
2. Observing Reports. Ray Will: trying to determine his exact longitude by the moon's of Jupiter. So far, no luck with the clouds. Chris Stevenson: fog. Randy Dodge: sundogs. The sun is quite active this year.
3. Observing Group. Gary Case noted we would try to get out as a group to the Butterpot site over the next two weeks. It appears there will be no comets this summer. Venus will be an early morning object this summer. Mercury will not be an easy object this summer. Saturn will be a late night object later in the summer. Jupiter is best observed in the twilight now, while it is still away from the horizon. Uranus and Mars will be close together. The Perseids are badly timed with the moon this year. More on mars: some pictures of how mars will look now versus two months from now (14" to 25" in size). A 4-inch telescope should be sufficient to view Mars now. Star-B-Que will be on August 1-3. We will also try to get out as a group during the new moons just before and after SBQ.
4. Randy: Some brief notes on where the SETI screensaver project is now.
5. Chris Stevenson on nebula. Chris gave a seminar to the Physics Department last week. His brief talk will go over that seminar, leaving out the equations and such. The talk will be on HII regions, or Diffuse Nebula. This stuff is made out of glowing gas, lit by one or more stars from within. These stars are usually hotter supergiants, upwards of 100 solar masses, and are particularly intense in the ultra-violet, which gives the nebula its characteristic glow (particularly from hydrogen emission lines). The stars typically have a temperature above 30 000 Kelvin. The HII region itself is in the 8000 Kelvin region. The difference in temperature is explained by the fact that the glow (light) from the nebula carries away the excess energy in all directions.
A HII region is usually characterised by dust and gas, a cluster of one or more OB stars (supergiants) and wind blown voids, producing a clumpy texture in the HII region (OB stars typically have very strong winds). A perfect example is something familiar to most amateurs, the Orion Nebula. It is interesting to note that the Orion Nebula as a visual object consists of the main diffuse nebula, lit from within by the UV light of the OB stars, and also a secondary nebula, called a reflection nebula. This latter nebula is reflected light from the main nebula and appears a distinctive blue due to the scattering of light from dust particles. (Special note: there is a reflection component in the main nebula, but it is overwhelmed by the UV light.)
Despite appearing so magnificent and cloud-like, HII regions are still an excellent vacuum. Light years of gas and dust are required in the line of sight in order for anything to be seen at all.
Chris displayed the Rosette nebula as an example of the structure seen in a typical HII region. There are globules and a hollowed-out area in the centre (the latter due to stellar winds). Chris also showed a shot of the X-ray part of the spectrum from the Chandra X-ray telescope.
In our galaxy HII regions dot all arms at all radii. They each have a spectra that is not continuous, but made up of discrete lines. Some examples of things that are not diffuse nebula: SNR (super-nova remnants) and PNe (planetary nebula: which is not a birth object, but a death object). An example of a supernova remnant would be the Gum nebula (45 degree spread across the sky) and of a planetary nebula would be the familiar Ring Nebula (M57).
6. Wine and Cheese.
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