1. A History of the Universe Astronomy 315 Professor Lee Carkner Lecture 2

2. Practice Observing  Write your name (clearly!) at the top of each exercise!  Label all constellations and bright stars  Always face due N or S  Always fill in completely Object, Location, Date and Time and Notes

3. Our Place in the Universe  Before we look at the history of the universe, we will look at our place in it   We now realize that we occupy no unique or special place in the universe   After Nicolaus Copernicus who theorized that the sun, and not the Earth, was the center of the solar system  So where are we?

4. The Solar System

5. Where Do We Fit In?  We can think about our position in the universe in terms of scale   Planet is in a planetary system around a star (Solar System)   Galaxy is in a cluster (Local Group)   Supercluster is in a (the?) universe  Each “step up” is a huge increase in size

6. Scale Models  We want to make a scale model to try to understand astronomical distances  Need to find the scale  example: miles per inch or light years per cm  Once you have the scale you can find the model size for any real object (model size) = (real size) / scale

7. The Big Bang  The best model for the beginning of the universe is the hot big bang model  Key points:   The early universe was very hot  Th  Why do we believe this?  The universe looks like it is expanding from a hotter, denser state

8. About the Big Bang  We can see the expansion of the universe and the glow of the early hot universe   The universe has a beginning but no center or edge   The universe is not really like any macroscopic object we are familiar with

9. The First Three Minutes  What was the early universe like?   What do we know?   Universe consists of photons and subatomic particles (like quarks)  Universe went through an early period of very rapid expansion called inflation   Cooled to the point where atoms could form after about 1 million years

10. Formation of Structure  After about 1 billion years the universe is a big ball of atoms and photons   Why?   This is why we have matter organized into stars, galaxies and clusters of galaxies, instead of a big uniform cloud of stuff

11. The Early Stars  The first stars were made out of hydrogen and helium, the two simplest elements   Nuclear reactions inside the stars produced heavier elements   Most of the universe (80%) is still hydrogen, however

12. Stellar Products  The next generation of stars had small amounts of these heavier elements in them   When any star dies it leaves behind a burned out core   Collectively known as compact objects

13. Composition of the Universe   Galaxies made up of:  “Normal” stars (maybe with planets)   Gas (hydrogen) and dust (heavier elements)

14. The Future   What effects the future of the universe?  Mass   If universe has enough mass, gravity might stop expansion  Dark energy   If there is enough dark energy it might rip universe apart

15. The Fate of the Universe  Possible ends for the universe  Big Crunch  Gravity pulls universe back into a point source   Big Rip  Dark energy rips universe apart   Big Chill  Universe expands forever 

16. Next Time  Read Chapter 1.1-1.5  Meet in Planetarium on Friday!