AST section 3.odt

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Astronomy & Astrophysics
Michael Reid

3.1/3.2 TheAncient Roots of Science/Ancient Greek Science – The milky way is disc shaped – Our solar system is located a little more than half way from the galactic centre to the edge of the galactic disc – The milk way is one of the largest galaxies out of 40 Galaxy clusters: Galaxies with a few dozen members Superclusters: Regions where galaxies and galaxy clusters are tightly packed (clusters of galaxy clusters) – The universe is expanding, average distances b/w galaxies is expanding – 14 billion years ago expansion began (beginning of the Big Bang) – Early universe had only hydrogen and helium, other elements were made by stars – Our solar system was made 4.5 billion years ago – Astar is born when gravity compresses the material in a cloud until the centre becomes hot enough to create energy by nuclear fusion – Astar dies when it runs out of fuel, new stars born from leftover matter *recycling plants Nuclear fusion: Process in which light weight atomic nuclei smash together/fuse to make heavier nuclei Supernovae: Massive stars die in titanic explosions – The farther away we look in the distance = the farther back in time we are looking – looking at a star 8 LY away we see how it was 8 years ago – We can't see something 15 billion LY away because we'd be looking back to a time when the universe didn't exist TIME – Ancient civilizations used the angles of the moon to predict rainfalls – Egyptians divided time into 12 parts – 1500 BC star clocks were abandoned for water clocks (hour glasses) – 16ths water clocks replaced by mechanical clocks – 20 century mechanical clocks replaced by electrical clocks – Templo Mayor inAztec city: a single dagger of sunlight would appear at noon Lunar calendars: 12 months, 11 days short of a sun calendar Metonic cycle: the dates in which lunar phases repeat Archaeoastronomy: Study of ancient structures in search of astronomical connections Geocentric model/Aristotle: Earth @ the centre, everything is spherical and floating around working like gears Ptolemaic model: Earth @ centre, planets circle as they orbit around the earth 3.3 The Copernican Revolution Copernican revolution/ Nicholas Copernicus: We learned earth orbits the sun Tycho: the best naked eye observer Kepler: hired by Tycho, discovered orbits aren't circles they are ovals (ELLIPSES) eccentricity: Quantity describing how much an ellipses stretched out compared to a perfect circle which has 0 Foci: Location of the two tacks Normal circle Ellipse Kepler's Laws #1: Each planet's orbit is an ellipse with the sun at one focus (end) and nothing at the other perihelion: closest point to the sun aphelion: farthest point
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