Ph.D. (1909) Indiana University

Transcription

1 4.!! Ph.D. (1909) Indiana University

2 Lowell Observatory, Flagstaff, Arizona Assistant Director (1915) Acting Director ( ) Director ( )! discovered blue-shift of the Andromeda nebula (1913)

3 The Radial Velocity of the Andromeda Nebula Slipher (1913) The nebulae are generally spiral in form and such nebulae exist in far vaster numbers than had been supposed. The Andromeda Nebula is approaching the solar system with a velocity of about 300 kilometers per second. The extension of this work to other objects promises results of fundamental importance, but the faintness of the spectra makes the work heavy and the accumulation of results slow.

4 As the 1920s drew toward a close, astronomers were finding hints of an even stranger phenomenon: the smaller, fainter, and thus presumably more distant a nebula was from Earth, the greater its red-shift. Hubble asked an assistant, Milton Humason, to train the 100-inch Mount Wilson telescope on some distant nebulae and see how their spectra behaved. Even more than Henrietta Leavitt, Humason seemed an unlikely candidate for the astronomical hall of fame. He began his career at Mount Wilson as a mule driver, carrying material and supplies up the mountain. He married the daughter of the observatory engineer and talked his way into a job as janitor.

5 Given the chance to learn how to make photographic plates, he quickly proved himself to be a very good photographer of starlight and was promoted to assistant astronomer. He had a grade school education. In the following weeks, Humason measured more red-shifts while Hubble scrutinized the results. By now he had compiled a list giving the recessional velocities of forty-six nebulae. Speed indeed seemed to increase with distance, and in a delightfully straightforward way. The relationship was what a mathematician calls linear.

6 (1929)

7 A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae Edwin Hubble (1929) Determinations of the motion of the sun with respect to the extragalactic nebulae have involved a K term of several hundred kilometers which appears to be variable. The results establish a roughly linear relation between velocities and distances among nebulae for which velocities have been previously published, and the relation appears to dominate the distribution of velocities. The outstanding feature is the possibility that the velocitydistance relation may represent the de Sitter effect, and hence that numerical data may be introduced into discussions of the general curvature of space.

8 Arthur Eddington! ( ) Second by second, the galaxies grow wider apart like dots on an inflating balloon. 1933: The Expanding! Universe And if you could reverse the clock, everything would become closer and more compact, converging on a single point. The big bang. The universe had a beginning. If the big bang theory was correct, then the size of the universe was an indicator of its age.

9 Mt. Wilson Observatory 100 inch Hooker Telescope George Hale, director It was the biggest blunder of my life. A. Einstein (1931)! (static universe; cosmological constant, 1917)

10 (H)!! km/s/mpc 67.0 km/s/mpc! km/s/mpc 71.0 km/s/mpc 70.4 km/s/mpc!! = 1/H! = 1/(71 km/s/mpc)! = (1 Mpc)/(71 km/s)!! 1 Mpc = (3.26)(10 6 )(3 x 10 5 km/s)(y) = (9.8 x km/s)(y)!! = (9.8 x km/s)(y)/(71 km/s/mpc)! = 1.38 x y (138 )

11 (Olbers Paradox)! ( )! Heinrich Olbers!

12 !!! Desiderata!!!!! Max Ehrmann (1927)!! Go placidly amid the noise and haste, and remember! what peace there may be in silence.!! You are a child of the universe, no less than trees and the stars;! you have a right to be here.! And whether or not it is clear to you, no doubt the universe is unfolding as it should.! Therefore be at peace with God, whatever you conceive him to be, and whatever your labors and aspirations, in the noisy confusion of life keep peace with your soul.! With all its sham, drudgery and broken dreams, it is still a beautiful world.! Be careful.! Strive to be happy.