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Astronamy Lecture Notes 1.docx

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University of Waterloo
SCI 238
Niayesh Afshordi

Our Place in the UniverseStarA large glowing ball of gas generates heat and light through nuclear fusionPlanetA moderately large object that orbits a star shines by reflected light rocky icy or gaseous in compositionMoon or SatelliteAn object that orbits a planeto The terms are interchangeable but artificial objects are always called satellitesAsteroidA relatively small and rocky object that orbits a star o Nonspherical shape small objects are often nonspherical gravity is not strong enough to compress the material into a sphereo Asteroids often called minor planets because they orbit much like planets but are smaller than anything we consider to be a true planetCometA relatively small and icy object that orbits a star Tails only occur when close to the Sun not when they are much farther awaySolar Star SystemA star and all the material that orbits itGalaxyA great island of stars in space all held together by gravity and orbiting a common center UniverseThe sum of all matter and energy How did we come to beThe universe is expanding from the Big Bang Based on the observed rate of expansion he universe is about 14 billion years old The expansion continues to this day except where gravityhas won stars galaxies clustersGalaxies make possible the formation of stars and recycle material through generations of starsAlthough the universe began with only the chemical elements HHe stars havecreated the elements from which rocky planets are made How can we know what the universe was like in the pastwe see objects as they were in the past The farther we look in distance the further back we look in time ie we see Orion Nebula 1500 years ago 1lightyearspeed of light1 yearkm365 days24 hr60 min60 s300000s1 yr1 day1 hr1 min9460000000000 km The Scale of the Universe1to10 billion scaleSun14cm diameter Earth1mm diameterWalk to Pluto is a few minutesDistance to Alpha Centauri is 2500 miles How big is the Milky Way Galaxy The Universeabout 100 billion starsThe Milky Way is one of about 100 billion galaxies11112210 starsgalaxy x 10 galaxies10 starsMoving EarthRotationmost of us are moving in circles around the axis at speeds far faster than commercial jets travel which is why jets cannot keep up with the Sun when going opposite Earths rotation Orbitat an average distance of 1 AU150 million kilometers Orbitwith Earths axis tiltedby 235 pointing to Polaris OrbitIt rotates in the same direction it orbits counterclockwise as viewed from above the North Pole High speed of over 100000 kmhr Moving SunOur Sun moves randomly relative to the other stars in the local solar neighborhood and orbits the galaxy every 230 million years typical relative speeds of more than 70000 kmhrThese two motions are known as motion with the local solar neighborhood and rotation of the Milky Way Galaxy
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