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Introduction Cosmology Cosmetics Cosmetology ..Greek words, kosmos, meaning “order,” “harmony,” and “the world,” and logos, signifying “word” or “discourse”. (Enc. Britannica) Cosmology is the study of the origin and evolution of the Universe Everything? Scientific Cosmology attempts to account for the origin and evolution of the Universe on the basis of laws of Physics. Large scale (galaxies) and small scale (elementary particles, e.g., electrons) Large scale => gravity Small scale => laws of quantum mechanics What is “scientific”? The description uses models What is there to describe? Main features Stars, Galaxies, blackholes etc. (large scale) Protons, electrons etc. (small scale) The in-between are “details” What is and what is not Science? A scientific theory is acceptable if: it can explain all relevant existing observations it can correctly predict observable phenomena Thus, a scientific theory inherently includes ways to verify/falsify itself. Example: Lightning occurs when Zeus throws his thunderbolts. Is it a scientific explanation? Why not? Describing our neighborhood Moon Planets (Jupiter, Mars, Saturn etc) and Satellites Sun Asteroids Comets Kuiper belt Oort cloud THAT’S THE SOLAR SYSTEM (1 star only, the Sun) Distances of objects in the Solar system Earth to Moon: 0.4 million km (0.4 x 106 km) Sun to Mercury: 58 x 106 km Earth to Sun: 150 x 106 km New unit of distance (1 AU = Astronomical Unit) 1 AU = 150 x 10 6 km Earth to Sun: 1 AU Sun to Mercury: 0.38 AU Sun to distant Comets: 15 trillion km, or 100,000 AU Objects beyond the Solar System Stars Blackholes Galaxies Nebulas etc, etc Distances of objects beyond the Solar System Our distance to Nearest Star 260,000 AU Unit of distance for objects beyond the Solar System Light year (ly) 9.5x1012 km Nearest Star is Proxima Centauri 4.23 ly Sirius (brightest star) 8.6 ly Deneb 3,000 ly Milky Way (visible stars) Galaxies Local Group Clusters and Super Clusters of Galaxies