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

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

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.

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

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

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

Our Cosmic Address STEWARD OBSERVATORY Ca. 1930

Steward Observatory THE UNIVERSITY OF ARIZONA

Steward Observatory The University of Arizona TUCSON

Steward Observatory The University of Arizona Tucson ARIZONA

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

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

Planet Diameter = 7900 miles Mass = 6x10 24 kilograms Age = 4.5 billion years = 4.5 x 10 9 years = 4,500,000,000 years

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

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)

Solar system to scale: SUN

THE SUN Visible light image 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.

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 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 miles THE MOON IS ABOUT 1.3 LIGHT SECONDS FROM EARTH THE SUN IS ABOUT 8.3 LIGHT MINUTES FROM EARTH

Practical matters: Astronomers use scientific notation to write large & small numbers = 1,000,000,000 = = 2,200,000 = x 10 6

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 = = 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 = = 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 = = 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.

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

STARS NEAR 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 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.

Space Travel Freeway speed Jetliner speed Concorde Speed (Mach 2) Spacecraft Speed Speed Freeway speed75 mph Jetliner speed500 mph Concorde Speed (Mach 2) 1350 mph Spacecraft Speed 40,000 mph SpeedTime to get to Mars Time to get To Jupiter Freeway speed75 mph80 years600 years Jetliner speed500 mph12 years90 years Concorde Speed (Mach 2) 1350 mph 4.4 years33 years Spacecraft Speed 40,000 mph 2 months1.5 years SpeedTime to get to Mars Freeway speed75 mph80 years Jetliner speed500 mph12 years Concorde Speed (Mach 2) 1350 mph 4.4 years Spacecraft Speed 40,000 mph 2 months SpeedTime to get to Mars Time to get To Jupiter Time to get to Saturn Freeway speed75 mph80 years600 years1200 years Jetliner speed500 mph12 years90 years180 years Concorde Speed (Mach 2) 1350 mph 4.4 years33 years66 years Spacecraft Speed 40,000 mph 2 months1.5 years3 years SpeedTime to get to Mars Time to get To Jupiter Time to get to Saturn Time to get to Alpha Centauri Freeway speed75 mph80 years600 years1200 years38 million years Jetliner speed500 mph12 years90 years180 years6 million years Concorde Speed (Mach 2) 1350 mph 4.4 years33 years66 years2 million years Spacecraft Speed 40,000 mph 2 months1.5 years3 years70,000 years

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

Spiral Galaxy