Astronomy 170: The Physical Universe

1. Astronomy 170: The Physical Universe Prof. Jill Bechtold Graduate TAs: Johanna Teske, Megan Reiter All Students: Pick up 3 white handouts Honors: Pick up 4th handout on black cart

2. The Textbook: Recommended, Not Required The Cosmic Perspective By Bennett, Donahue, Schneider, & Voit 6th edition 5th edition OK, but there are always updates An ebook version is also available

3. Do I need to buy the book? • Class notes will be posted • Exams will be on lecture material • If you like to also read the material in a textbook, get the Bennett et al. book • New books come with a key to use the publisher’s web site, Mastering Astronomy, which has “flash cards”, quiz questions, and other study aides.

4. Honors Credit • If you want honors credit for this class, be sure you are signed up for Section 3. • If you are in Section 2 and want honors credit, please bring a change of class form for me to sign as soon as possible • Trip to Sky Center on Mt. Lemmon • We will have an organizational meeting later in the semester

5. What Is Modern Astronomy? • Science of the nature of everything outside of the Earth’s atmosphere: planets, stars, interstellar gas, galaxies, etc. • What is the content of the Universe? • What is its history? What is its future? • How do humans fit in? "My goal is simple. It is complete understanding of the universe, why it is as it is and why it exists at all. " -- Stephen Hawking

6. Goals of this course • Survey of current state-of-the-art • astronomy and astrophysics • Science literacy in the physical sciences; • current topics • See how working research scientists think

7. Our Cosmic Address STEWARD OBSERVATORY Ca. 1930

8. Steward Observatory THE UNIVERSITY OF ARIZONA

9. Steward Observatory The University of Arizona TUCSON

10. Steward Observatory The University of Arizona Tucson ARIZONA

11. Steward Observatory, The University of Arizona Tucson, Arizona UNITED STATES, NORTH AMERICA

12. Steward Observatory, The University of Arizona Tucson, Arizona United States, North America EARTH

13. EARTH • Planet • Diameter = 7900 miles • Mass = 6x1024 kilograms • Age = 4.5 billion years • = 4.5 x 109 years • = 4,500,000,000 years

14. Earth has one moon, which orbits it The Moon Earth-Moon distance = 240,000 miles or 30 Earth Diameters

15. Steward Observatory, The University of Arizona Tucson, Arizona United States, North America Earth SOLAR SYSTEM (Not to scale) SUN, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, (Pluto)

16. Solar system to scale: SUN

18. THE SUN • Star, produces energy by nuclear fusion (Hydrogen  helium) • THE SUN • Star, produces energy by nuclear fusion (Hydrogen  helium) • 93 million miles from Earth • 93 million miles = 1 Astronomical Unit, or A.U. THE SUN Visible light image

19. More on units of distance: • Instead of miles, kilometers, etc. astronomers often • use light seconds, light minutes, light years • 1 Light Year = the distance light travels in one year More on units of distance: • More on units of distance: • Instead of miles, kilometers, etc. astronomers often • use light seconds, light minutes, light years • More on units of distance: • Instead of miles, kilometers, etc. astronomers often • use light seconds, light minutes, light years • 1 Light Year = the distance light travels in one year • 1 Light Year = 5.9 x 1012 miles THE MOON IS ABOUT 1.3 LIGHT SECONDS FROM EARTH THE SUN IS ABOUT 8.3 LIGHT MINUTES FROM EARTH THE MOON IS ABOUT 1.3 LIGHT SECONDS FROM EARTH

21. Practical matters: Astronomers use scientificnotation to write large & small numbers. 1000 = 1,000,000,000 = 0.001 = 2,200,000 = 103 109 10-3 2.2 x 106

22. 1 light minute = the distance light travels in one minute 1 light year = the distance light travels in one year = almost 10 trillion kilometers or 6 trillion miles (one trillion = 1012 = 1,000,000,000,000) 1 light minute = the distance light travels in one minute 1 light year = the distance light travels in one year = almost 10 trillion kilometers or 6 trillion miles (one trillion = 1012 = 1,000,000,000,000) Because light takes time to travel through space, when we look farther away in distance, we look farther back in TIME. 1 light minute = the distance light travels in one minute 1 light year = the distance light travels in one year = almost 10 trillion kilometers or 6 trillion miles (one trillion = 1012 = 1,000,000,000,000) Because light takes time to travel through space, when we look farther away in distance, we look farther back in TIME. The farthest we can see in space is 13.7 billion light years, because we think the Universe is 13.7 billion years old.

27. Orbit of Quaor (Q) and Pluto (P) versus the planets

29. STARS NEAR THE SUN

30. Nearest Star to Sun: Alpha Centauri • Triple star in S. hemisphere • 4.2 light years from the Sun • Nearest Star to Sun: Alpha Centauri • Triple star in S. hemisphere • Nearest Star to Sun: Alpha Centauri • Triple star in S. hemisphere • 4.2 light years from the Sun • Alpha Centauri A and Alpha Centauri B are orbiting each other • with period 80 years, separation 23 Astronomical Units. • Nearest Star to Sun: Alpha Centauri • Triple star in S. hemisphere • 4.2 light years from the Sun • Alpha Centauri A and Alpha Centauri B are orbiting each other • with period 80 years, separation 23 Astronomical Units. • Proxima Centauri is 13,000 AU from Alpha Centauri A and B.

31. Space Travel

33. Back to our COSMIC ADDRESS Steward Observatory, The University of Arizona Tucson, Arizona United States, North America Earth Solar System Milky Way Galaxy: The Sun is one star of many in the Milky Way The Milky Way as seen from Earth

34. Spiral Galaxy