We had the sky up there, all speckled with stars, and we used to lay on our backs and look up at them, and discuss about whether they was made or only just happened—Jim he allowed they was made, but I allowed they happened; I judged it would have took too long to make so many.
-Huckleberry Finn
That in blessing I will bless thee, and in multiplying I will multiply thy seed as the stars of the heaven, and as the sand which is upon the sea shore
-Genesis 22:17
There are as many stars in a galaxy as there are cells in your brain. Use your 100 billion brain cells to think about that one...
Visible from night sky
Infrared map of our sky reveals Milky Way structure
Inferred Structure of Milky Way [Harlow Shapley and the human "computers", circa 1920's]
Center of galaxy: 3.7 million solar mass black hole (!?)
Our neighbor Andromeda (spans 4 degrees, also called M31)
What are the spiral nebula or island universes? [Shapley-Curtis debate, 1920]
Galactic zoo
General properties of galaxies (spiral, elliptical and irregular galaxies. Table)
Mapping our neighborhood (taken from Richard Powell's maps)
Hubble Ultra Deep Field (HUDF) studies an "empty" 3-arcminutes of sky (img1, img2). Think looking into tiny space defined by an eight-foot-long soda straw.
2dF Galaxy survey to 2 billion light years
2MASS panoramic image of 1.6million galaxies (a fraction of the total number thought to exist which is estimated at 100-billion)
Computer simulations of large scale structure of universe
Galactic spectra show strong redshift
Hubble's Law relates redshift to distance [Chaisson section 24-3]
Allows determination of overall "size" and age of Universe [Chaisson Table 24-2]:
Visualizing cosmic structure:
Lab exercise: Build a scale model of the known universe.
Earth ~ proton (1 femto-meter diameter)
Here's a illustration of the model
All scales are approximate; what is important here is to get a intuitive feel for the system.
Chaisson text:
The Two Micron All Sky Survey (2MASS)
Cosmology and galaxy formation resources from the Kavli Institute for Cosmological Physics
(others are linked directly above)
Document URL: http://www.uh.edu/~jclarage/astr3131/lectures/11/11.html
