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Unformatted text preview: Universe Astronomy 307 - 1st meeting Aug. 26, 2010 Introducing the Universe
Course Structure and Syllabus Setting the Scene: the cast of characters Measurement: scientific notation & units The Cast of Characters Ast 307 8/26/10 Ast 307 2 Universe Star
A large, hot ball of gas that produces its own light (usually) by means of thermonuclear fusion reactions The total of everything: all matter and energy in and between galaxies Ast 307 8/26/10 Ast 307 4 Planet Moon Ganymede (a moon of Jupiter) A moderately large object that orbits a star and shines by reflected light. A planet may be rocky, icy, or gaseous.
8/26/10 Ast 307 5 An object that orbits a planet…not necessarily Earth!
8/26/10 Ast 307 6 Asteroid
A small, rocky object that orbits a star. Comet “Solar” or Planetary System
A star and all the material which orbits it, including its planets and moons The nucleus is a small, icy body orbiting a star. The tail is a thin (low density) stream of gas and dust.
8/26/10 Ast 307 7 8/26/10 Ast 307 8 Interstellar Nebula
Clouds of low-density material in space, between the stars (“interstellar clouds”) Nebulae Created by Stars
Supernova Remnant: debris from an explosion Planetary Nebula: cast-off outer layers of a lower-mass star What are the dark lanes? 8/26/10 Ast 307 9 8/26/10 Ast 307 10 Galaxy
A large system of stars and gas, held together by gravity (an “island universe”) Scales of Things in the Universe Astronomers use scientific (exponential) notation to deal with objects that span a very wide range in sizes
8/26/10 Ast 307 11 8/26/10 Ast 307 12 Hierarchy of the Universe
Note numbers in exponential notation and expressed in “special” units namely AU and ly (light years)
Ast 307 The Meaning of a Light-year
A light-year is a unit of distance, not time: It’s the distance light travels in one year.
1 light - year = (speed of light) " (1 year) # km & # 365 days 24 hr 60 min 60 s & " " " = % 300,000 ( "% ( $ 1 day 1 hr 1 min ' s ' $ 1 yr = 9,460,000,000,000 km
= 9.46 ! 1012 km = 9.46 ! 1015 m 8/26/10 Ast 307 14 ...
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- Fall '10