Download earth - University of Arizona

8/23/11 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 The Textbook: Recommended, Not Required The Cosmic PerspecGve By BenneI, Donahue, Schneider, & Voit 6th ediGon 5th ediGon OK, but there are always updates An ebook version is also available 1 8/23/11 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 BenneI et al. book •  New books come with a key to use the publisher’s web site, Mastering Astronomy, which has “flash cards”, quiz quesGons, and other study aides. Honors Credit •  If you want honors credit for this class, be sure you are signed up for SecGon 3. •  If you are in SecGon 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 organizaGonal meeGng later in the semester 2 8/23/11 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 scienGsts think 3 8/23/11 Our Cosmic Address STEWARD OBSERVATORY Ca. 1930 Steward Observatory THE UNIVERSITY OF ARIZONA 4 8/23/11 Steward Observatory The University of Arizona TUCSON Steward Observatory The University of Arizona Tucson ARIZONA 5 8/23/11 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 6 8/23/11 EARTH •  Planet •  Diameter = 7900 miles •  Mass = 6x1024 kilograms •  Age = 4.5 billion years = 4.5 x 109 years = 4,500,000,000 years Earth has one moon, which orbits it Earth-­‐Moon distance = 240,000 miles The Moon or 30 Earth Diameters 7 8/23/11 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 8 8/23/11 THE SUN •  Star, produces energy by nuclear fusion (Hydrogen  helium) •  93 million miles from Earth •  93 million miles = 1 Astronomical Unit, or A.U. Visible light image 9 8/23/11 More on units of distance: •  Instead of miles, kilometers, etc. astronomers o\en 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 10 8/23/11 PracGcal maIers: Astronomers use scien&fic nota&on to write large & small numbers. 1000 = 103 1,000,000,000 = 109 0.001 = 10-­‐3 2,200,000 = 2.2 x 106 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 Gme 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. 11 8/23/11 12 8/23/11 13 8/23/11 Orbit of Quaor (Q) and Pluto (P) versus the planets 14 8/23/11 STARS NEAR 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 orbiGng each other with period 80 years, separaGon 23 Astronomical Units. •  Proxima Centauri is 13,000 AU from Alpha Centauri A and B. 15 8/23/11 Space Travel Speed Time to get Time to get to Mars To Jupiter Time to get to Saturn Time to get to Alpha Centauri Freeway speed 75 mph 80 years 600 years 1200 years 38 million years Jetliner speed 500 mph 12 years 90 years 180 years 6 million years Concorde Speed (Mach 2) 1350 mph 4.4 years 33 years 66 years 2 million years 40,000 mph 2 months 1.5 years 3 years 70,000 years Spacecrap Speed 16 8/23/11 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 17