1. Astronomy 103 Lecturer: Prof. Alex Lazarian Office Location: 6289 Chamberlin Hall Email: lazarian@astro.wisc.edu Website: http://www.astro.wisc.edu/~lazarian/ast103_2014/ Office Hours: Mon. 11am-1pm, Wed. 11am-1pm. Meetings at a different time can also be arranged. Course Reading: Pathways to Astronomy Schneider & Arny 4nd edition Exams: 0 th training exam -- 0% (Oct. 6) 1 st exam – 25% (Oct. 16) 2 nd exam—25% (Nov. 10) final exam—30% (Dec. 15) total for homework, quizzes, presentations -- 20% Main Ideas to be covered: *Subject of astronomy (Units 1--4) *Observations of planets and stars (Units 5--12) *Laws of gravity, dark matter (Units 14-20) *Light, atoms, spectra (Units 21--30) *Stars: Sun as an example (Units 49--50) *Learning about stars (Units 52--55) *Birth and evolution of stars (Units 56—63, 69) *When the fuel begins to run out (Units 64--66) *Supernova, neutron stars and black holes (Units 67--68) *Galaxies and quasars (Units 74--77) *Our galaxy- Milky Way (Units 70--73) *The expanding Universe (Units 78--82) *Life in the Universe (Units 83--84) *Review of the course

2. The Solar System Planets, asteroids, comets and dust all held together by the Sun ’ s gravity Everything goes around the Sun on elliptical paths called orbits All orbits lie in the same plane, like peas rolling around on a dinner plate Too big to describe using meters – we need something more convenient

3. A convenient measure – the Astronomical Unit It is convenient to measure planetary distances using the Astronomical Unit, or AU 1 AU = average distance between the Earth and the Sun 1 AU ~ 150 million km Some planetary distances: Mercury: 0.4 AU Mars: 1.5 AU Saturn: 10 AU Pluto: 40 AU

4. The Milky Way Galaxy The Milky Way galaxy contains billions of stars, being born, aging and dying with a whisper or a bang. Where do stars come from? How do they age? How and why do they die? This process is called Stellar Evolution!

5. A New Measure of Distance Stars in the Milky Way are very far apart –Nearest star is 40 trillion km away – too large to imagine! –How about hundreds of thousands of AU? No, still too big. –Light travels 10 trillion km in one year, so we ’ ll use the light year (ly) as an easy-to-imagine measure of distance –It takes light 4.1 years to travel from Proxima Centauri to Earth, so the distance to this star is 4.1 ly.

6. Getting to Know the Neighborhood The Universe is “ clumpy ” – galaxies tend to pull together by gravity –Our immediate neighborhood is called the Local Group, a cluster of around 3 dozen galaxies (3 million light years across –The Local Group is part of the Virgo Cluster, a large (collection of smaller clusters and groups of galaxies –Superclusters: collection of larger clusters –The Universe – simply everything! Central region of the Virgo Cluster

7. A Sense of Scale I

8. A Sense of Scale II

9. Outward to the Universe!

10. The Metric System Metric Units are internationally accepted Units. Used in Astronomy. English Units (Distance) 12 “ lines ” =1 inch 12 inches=1 foot 3 feet=1 yard 5.5 yards=1 rod 4 rods=1 chain 10 chains=1 furlong 8 furlongs=1 mile 3 miles=1 league Metric Units 10 millimeters=1 centimeter 100 cm=1 meter 1000 m=1 kilometer 1000 milligrams=1 gram 1000 g=1 kilogram

11. 0.0000001 meters is difficult to write – too many zeros! Can use scientific notation to simplify it. 0.0000001 m = 1  10 -7 Move the decimal place seven places to the left to determine the “ power ” of ten –Moving it to the left makes the “ power ” negative –Moving it to the right makes the “ power ” positive Scientific Notation Commonly used prefixes Number Scientific Notation Prefix Abbreviation 1,000,000,000 1  10 9 giga G 1,000,000 1  10 6 mega M 1,000 1  10 3 kilo k 0.01 1  10 - 2 centi c 0.001 1  10 - 3 milli m 0.000001 1  10 - 6 micro  0.000000001 1  10 - 9 nano n

12. Special Units The Light Year (ly) –Distance light travels in 1 year –Equivalent to a “ look- back time ”, as the light we see from a star left a long time ago –Example: Proxima Centauri is 4.1 ly away, so the light we see from it today left the star 4.1 years ago! The Parsec (pc) –“ PARallax SECond ” –Distance to a body whose parallax motion covers 1 second of arc (See Unit 5!) –1 pc = 3.26 ly

13. A Sense of Scale

14. The Scientific Method The Scientific Method is the procedure scientists use to construct their ideas about how the Universe works. –Start with a hypothesis – a testable idea of how something works –Test the hypothesis! –If the test fails, modify or abandon the hypothesis, and retest. Hypotheses that pass rigorous testing become Laws (more mathematical) or Theories (described using both words and equations). A Model is a complex description of physical phenomena incorporating many laws and/or theories –Ex: The Celestial Sphere –Ex: Universal Gravitation

15. The Nature of Matter Protons (positively charged) and neutrons (uncharged) make up the nucleus at the center of an atom. Electrons (negatively charged particles) are found relatively far from the nucleus –If we enlarged the nucleus to be the size of a grape, the electrons would orbit at a distance of slightly less than a football field! –Most “ solid ” matter, then, is made up of mostly empty space!

16. Fundamental Forces in Nature Gravitational Force –Force between massive bodies –Infinite in range, but weakens with distance Electromagnetic Force –Force between charged bodies –Infinite in range, but weakens with distance Strong Force –Force that holds atomic nuclei together –Very short range – 10 -15 meters! Weak Force –Force responsible for radioactive decay –Very short range – 10 -18 meters!

17. Elementary Particles Smallest particles known are quarks, which make up protons and neutrons –Up quarks –Down quarks “ Up ” and “ Down ” are just labels Other kinds of quarks have labels like “ strange ” and “ charm ”, and again are just labels. The description of the universe and its contents using elementary particles is called The Standard Model.