1. Unit 1: The Big Picture

2. What is Astronomy? The study of stars & anything outside Earth –Not astrology…no horoscope reading here! Today we will go over –Universe Creation (how did it all begin?) –Universe Composition –Universe Size (how big is it??)

3. Universe Creation Big Bang Theory – universe literally explodes into existence. –Temperature: universe cooled from about 10 23 K to about 10 10 K within the first second –Temp dropped below 1 billion K after only 3 minutes, to 3000K after a million years, to 300K today *Water freezes at 273K and boils at 373K –10 23 = 1,000,000,000,000,000,000,000,000

4. A few artists’ renditions of the Big Bang

7. Size Increased in size by 10 30 in less than 10 -30 sec. (started out the size of an atom and grew instantly to the size of a galaxy) Continues to grow as galaxies are moving away from each other…Hubble’s Law Estimated age is 10-16 billion years So, it’s REALLY BIG, SUPER BIG, BEYOND COMPREHENSION

9. Composition 4 sec-temp too low for converting energy into matter, too high to form atoms 3 minutes – nuclei can form –25% helium nuclei, 75% hydrogen nuclei w/ small amounts of lithium and boron nuclei 300,000 years before temps cool enough to form atoms –25% Helium, 75% hydrogen mix

10. Composition Solar System: group of planets, moons, debris moving around a star Interstellar Space: space between stars filled with dust, gas, etc. Galaxy: systems of billions of stars –200 billion stars in the Milky Way –Billions of galaxies in universe each with potentially hundreds of solar systems

11. Are we alone??

12. Composition Continued Intergalactic Space: the space between galaxies. mostly nothing, can’t see it, gravitational pull toward it exists Galaxy Clusters: small group of galaxies –Closest is Sagittarius galaxy 75,000 LY, Magellanic Clouds, then Andromeda Superclusters: groups of galaxy clusters Cosmic Voids: space between superclusters

13. Milky Way Galaxy Galaxy Cluster

14. Important Distances *Astronomical Unit (AU) = distance from sun to earth (93 million miles) *62.25 AU = 1 light year = 6 trillion miles *Light year = distance light travels in 1 year

15. Is the light we see from stars and other objects in the sky “up to date”?

16. Important distances to put in all in perspective Earth’s diameter: 8,000 miles Solar System diameter: about 8 billion miles Distance to nearest star: 4.3 LY (Alpha Centauri) Distance across the Milky Way: 100,000 LY Distance to Andromeda Galaxy: 2.5 million LY Distance across local group: 4 million LY Distance across our supercluster: 100 million LY **Bottom Line: There are billions of galaxies in the universe each containing billions of stars!

17. Day 2: Galaxies Galaxy: systems of billions of stars, “island universes” –Thought Milky Way made up entire universe until 1920s –Small fuzzy patches in telescopes appeared as nebulae, Latin for clouds –Edwin Hubble measured approximate distance to nearby Andromeda…no way Milky Way was that large –3 Types: spiral, elliptical, irregular

18. Spiral Galaxies (Milky Way) Nucleus, halo, disk, spiral arms Gas & dust visible Spin in direction indicated by arms Barred spiral: bar of stars running through nucleus…page 505 in textbook for diagrams

20. Elliptical Galaxies Sphere or squashed sphere shape with nucleus and halo No spiral arms, little dust or gas Made almost entirely of old reddish stars Stars orbit, but not all in the same path…don’t rotate Range in size from giant to dwarf Dwarf is the most common type of galaxy

22. Irregular Galaxies Lacking regular shapes Large and Small Magellanic Clouds are among nearest neighbors which are –visible in the Southern Hemisphere –Look like clouds detached from Milky Way –Believed to be pulling apart due to gravitational pull from Milky Way

23. Our Home: The Milky Way Made up of 200 billion stars, dust and gas Gases absorb light from stars and give a band of light in the sky –Difficult to see stars in other spiral arms –Scientists use radio & infrared waves to penetrate dust Spiral arms due to trailing of larger stars more distant than smaller stars Black hole center Sun located on inner edge of Orion arm

24. Two types of stars: –Population I: bright blue stars in the spiral arms, younger stars ( 10 BY and younger, Sun) –Population II: located in the halo, bulge, and globular clusters, older stars (13 BY and older)

25. Milky Way Facts Diameter of disk100,000 LY Thickness of disk 2,000 LY Distance of Sun from Center 25,000 LY Number of Stars 200 Billion Time for Sun 200 Million years to make 1 circuit to make 1 circuit