Location: Chemistry/Physics Building, MUN
Time: 8:00 pm
Ben Llewellyn donated the "Reader's Digest Hilights: Voyage to the Planets". This is ultimately based on the BBC production "Planets".
The first half of the talk is based on Chris's NIE article (Newspapers in Education). This article can be found from our homepage. Spring is galaxy time. For example, there are many to be found in Ursa Major, straight overhead. Chris went to his NIE article, and started with M81/82 in the Big Dipper. He showed us how to find these and other nearby galaxies in the Big Dipper (M108/9, M51/101). We were also treated with extremely good amateur photos taken by Johannes Schedler of http://panther-observatory.com , rivalling professional ones. Although visible year-round in our area, Chris noted the Big Dipper is best in Spring. Leo is at its best only in the Spring (not well-situated or often even visible for the rest of the year). Chris took us on a tour of Leo: Leo triplet, M95/96 (Ring Galaxies), and the M95 Group. You can keep following the Milky Way. For example, nearby in Virgo one can find M87.
For the second half of the talk, Chris began with a brief history of Cosmology, starting with "Turtles all the Way Down" (http://en.wikipedia.org/wiki/Turtles_all_the_way_down). Chris then went through the evolution of cosmological ideas up to the discoveries of Hubble concerning the Cepheids and the expansion of the universe. The predicted age of the universe based on Hubble's constant is found to be in good agreement with data from the WMAP experiment. Chris also touched on General Relativity and Einstein's famous lambda-constant mistake.
Much closer to our century, Vera Rubin could not account for the solid disk-like rotation qualities of galaxies. The outer parts of galaxies should be more slowly rotating around the central portion than observed. Accounting for the known solid, luminous bodies in galaxies, there had to be four times that mass in a non-visible halo around galaxies. This was shown to be the case for galaxies in a cluster: the observed gravitational lensing (General Relativity) that resulted from a massive cluster could only occur if there was more mass involved than the visible mass of the cluster. By studying the arcs, a smoother distribution of mass is also implied (like a gas, not groupings of stars).
What is the nature of this non-luminous matter? The speculation ranges from baryonic to WIMPs. WIMP collisions would provide electron and positron pairs. Interestingly, the PAMELA satellite (Discover, April 09) has found a positron excess.
The amount of overall dark matter would determine if the universe is open, closed, or flat. To reach the "critical density" where the universe would be on the verge of being able to collapse back requires much more matter than is visible, or putatively exists in dark matter halos. Something more would be needed.
Chris explained how the expansion of the universe has been studied using standard candles (Type Ia supernovae). These indicate the universe has been expanding at an ever increasing rate. The 1998 SCP results, the confirmation with the High-Z Supernova search, and later Hubble results, providing better constraints, indicate that the universe is something like 72% dark energy.
The recent study of the Bullet Cluster appears to rule out modifications of Newtonian gravity (MOND), and instead points toward dark matter. The gravitational lensing arcs indicate something else is involved in the cluster dynamics other than baryonic matter, to a high level of confidence.
In April 2009 an article appeared in Scientific American on "Baryonic Acoustic Oscillations". The authors propose that the Local Group of galaxies is near the centre of an expanding super void (this requires a clumpy structure to the cosmos). By creating a special place for the earth (in the sense of being central in this void), the accelerating expansion of the universe can be explained by the apparent effects of being in the centre of this void. Also of note is the "Axis of Evil" in the Cosmic Microwave Background. Perhaps the Planck probe will help answer these questions.
Robert took over for Shawn and passed around Shawn's prepared sheet. Shawn covered the start up of the new solar cycle. Also covered were the Moon and Planets. Chris noted that sometime in the next week or two (see Sky and Telescope) there will be eclipses of some of Jupiter's moons. [This is going on most of this year.]
Terry showed us his Baader Zoom Hyperion. For a zoom eyepiece, this rivals other good single focal-length eyepieces. The zoom goes from 8-24 mm, and the views are pretty sharp. At $215 USD, they have forced Televue down in price.
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