To the Stars and Beyond University of Wisconsin – Eau Claire Continuing Education Dr. Nathan Miller Department of Physics & Astronomy WELCOME BACK!
Main topics of Course • Appearance and motions of night sky objects • Visit to the planetarium to see sky motions in 3D (we will walk over together) • Telescopes: design and basic use • The Lives of the Stars • The Universe and the Big Bang • Life in the universe and planets where it may be found
William Herschel (1738-1822) • Made first systematic study of nebulae and star distributions • Discovered planet Uranus (1781)
Shapley (1885-1972) mapped globular clusters MW is big, Sun not at center
Is the Milky Way the Entire universe? • Is the Milky Way big (S) or small (C)? • Are the “spiral nebula” galaxies like the Milky Way (C), or are they in the Milky Way (S)?
Shapley: The Milky Way is the entire universeCurtis: The Milky Way is but one of many galaxies
The Milky Way Galaxy • Basic shape: • disk 80,000 ly across, 1011 stars • spherical halo surrounding disk • central bulge • Our sun is • 28,000 ly from the center • orbital speed of 220 km/s • completes one revolution every 200 My
Galaxy spectrum is aggregate of the spectra of all the stars/nebulae of which it is composed
Compare wavelengths of observed lines to where those lines are in the laboratory
In most galaxies observed, lines shifted to longer wavelengths “redshifted”
Simplest interpretation – Doppler effectRedshift means galaxies are all moving away from us
Far Away Galaxy (we assume it is far away because it appears much smaller)
The farther away a galaxy is, the quicker it is fleeing from usThis is Hubble’s Law.
Does this mean the Milky Way is special (i.e. especially disliked)? • What would astronomers in other galaxies measure?
The graph is a straight line with a y-intercept of zero. • Mathematical form is y = mx • Galaxy velocity = slope times galaxy distance
If the middle, labeled line shown below corresponds to 72 km/s/mpc, which line would correspond to a Hubble constant of 144 km/s/mpc?
The slope is referred to as Hubble’s Constant (=H0). The current best value is 72 kilometers per second per megaparsec (km/s/Mpc)
Note H0 (km/s/Mpc) really has units of inverse time, because km and Mpc really measure the same thing.
The Cosmic Microwave Background Radiation (CMBR): some of the strongest evidence for the Big Bang
Look-back time: • As you look farther from Earth, you are looking back in time due to light travel time • You might think that you would see all the way back to the Big Bang, but the universe was so hot that it was fully ionized and not transparent
Big Bang Timeline (starting 12.7 billion years ago): • 10-43 sec- shortest time measurable • 10-6 sec – 1013 K – Protons and Neutrons can form from quarks • 15 minutes of deuterium and helium formation • 379,000 years – electrons combine with ions to form atoms, universe becomes transparent