29:50 Modern Astronomy
Fall 2002
Lecture 28 ...November 20, 2002
Galaxies and the Universe
A description of why the Leonids were fast, and why they were visible early in the morning.
(1) Last time, the size and shape of the Milky Way were discussed.
Infrared picture of the Milky Way....The Milky Way as a Galaxy
(2) Now we want to discuss the astronomy of other such systems in space: this is
Extragalactic Astronomy. Let's begin nearby, with the objects M31 and M33. Many of you have seen the first of these. These are the nearest large galaxies to the Milky Way.
SC1 chart of Andromeda and Triangulum.
(3) Images of the nearest spiral galaxies.
M31, the Andromeda Galaxy Distance 730 kiloparsecs
M33, Galaxy in Triangulum, distance = 670,000
NGC 604: super star formation region in M33
(4) Now, how are these systems organized? New insight...look at Appendices 13 & 14 of your book. Galaxies come in bunches. Local Version is the Local Group.
Image of the Local Group
(5) Important point, spirals are not the only kind of galaxies. There are also ellipticals and irregulars.
Image of a big elliptical, Centaurus A distance = 6.9 Megaparsecs.
(6) How far out does it go? Let's introduce another prototypical object, the Virgo Cluster.
The Virgo cluster is right in the ``bowl'' of the constellation Virgo. With binoculars, you can see fuzzy little galaxies. With telescope, you can see a lot more.
Picture of the Virgo Cluster
Facts about the Virgo cluster.
20 Megaparsecs = 65 million light years. The light you see was emitted from the stars in the Virgo cluster at the time of the extinction of the dinosaurs on Earth!
(7) How far out does it go? (continued). The Virgo Cluster is not the only ``rich cluster'' in the sky. Incredibly, it is only the closest!
Even in 1957, astronomical instruments were good enough to catalog huge numbers of these. Astronomer George Abell compiled a catalog of 2700 rich clusters of galaxies, of which Virgo is the closest
Map of the Abell Clusters
