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AS101 Textbook notes

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Victor Arora

AS101 TEXTBOOK NOTESSPRING TERM CHAPTER 1THE SCALE OF THE COSMOS SPACE AND TIME 11 From Solar System to Galaxy to Universe 8Astronomical unitaverage distance from Earth to the Sun 15x10kmSolar system consists of the Sun its family of planets and some smaller bodies such as moons asteroids and cometsPlaneta nonluminous body in orbit around a star large enough to be spherical and to have cleared its orbital zone of other objects o They shine by reflecting sunlightStarglobe of gas held together by its own gravity and supported by the internal pressure of its hot gases which generate energy by nuclear fusion eg sun o Selfluminous ball of hot gas that generates its own energySun is about 110 times larger in diameter than EarthLight from the Sun reaches Earth in only 8 minutesSun is a fairly typical star a bit larger than average and located in a fairly normal neighbourhood in the universe 13 Light year lyunit of distance equal to the distance light travels in one year roughly 10km or 63 000AUNearest star to the Sun is Proxima Centauri which is 42ly from EarthSizes of dots represent not the sizes of the stars but their brightnessTheres thin gas that fills the space between the stars o These clouds give birth to new starsGalaxylarge system of stars star clusters gas dust and nebulae orbiting a common centre of mass o Bound together by the combined gravity of all the matterMilky Waythe hazy band of light that circles our sky produced by the glow of our galaxyMilky Way Galaxythe spiral galaxy containing our Sun visible in the night sky as the Milky WayOur galaxy contains over 100 billion stars and has graceful spiral arms winding outward through the diskStars are born in great clouds of gas and dust as they pass through the spiral armsSpiral armslong spiral pattern of bright stars star clusters gas and dust Spiral arms extend from the centre to the edge of the disk of spiral galaxiesGalaxies are commonly grouped together in clustersClusters are grouped into superclusters clusters of clusters and the superclusters are linked to form long filaments and walls outlining voids that seem nearly empty of galaxiesThese filaments and walls appear to be the largest structures in the universe 12 The Cosmic Calendar Concepts of TimeIt has been about 137 billion years since the Big Bang the instant the universe commenced and the beginning of time itselfProblem in astronomy is keeping a proper sense of scale CHAPTER 2PATTERNS AND CYCLES 21 The StarsSun and stars rise in the East and set in the WestConstellationsone of the stellar patterns identified by name usually of myth gods people animals or objects region of the sky containing that star patternConstellation boundaries were only approximate
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