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Astronomy 2022A/B
Chris Racknor

Lecture 1 Universecosmosall spacematterenergy that is accessible to usCosmogeny cosmogenesis soft g birth startCosmogony hard g infancyEschatology chk senility last daysCosmothanatos death endEarth is flat sky is a domebelieved by early culturesGreeks introduced spherical earthEratosthenes in 240 BC measured earths diameter with no modern tools within 2 o Learned from shadow of columns o Sun is far light arrives almost parallel to itself at earth sun rays produce no column shadows in Syene but in Alexandria columns at Alexandria must be tilted with respect of the ones in SyeneHulldown Effect ship will have its mast and upper parts visible from the beach whilst being a few km offshoreGravity pulls to center of earthAristotle thought Earth was center of universe wrong o Thought if the earth was moving there would always be high winds o Stars seemed to spin on a single sphere o Planets are the reason points of light in the sky that were observed to move relative to the stars how sun and moon doNaked eye can see Mars Mercury Venus Jupiter SaturnConstellation of sun can be seen at night rise or setMoons motion against stars is fastesteasiest to see own width every hourPlanets seem to wander in a fixed rotation same as stars but overtime can be seen to move more slow relative to the starsPlanets motion is confined to a band of 12 constellations zodiacPtolemy Ideas o Believed Aristotles idea that the sun moon planets circled the Earth o Said planets sometimes travel backwards across the sky RETROGRADE MOTION o Had the idea that each planet moved in a small circle EPICYCLE WRONG o Epicycle too complex chunky only short time predictionsCopernican Theoryplanets move in circles around the SUN not earth o HELIOCENTRIC UNIVERSE geocentric is Earthcentred universe o Heliocentric universe PROS was simple explained why mercury and venus never travel far from sun natural explanations for season explanations of retrograde motions without relying on epicycles o Heliocentric universe CONS couldnt predict positions of planets couldnt answer why no high winds all the time if earth is moving good things move up dirty things move down flames up dirt down planets up stars upTycho Brahe1572 saw a new star in constellation Cassiopeia a SUPERNOVA1604 another supernova was discovered1609 Galileo made a spyglass for himself discovered 4 moons circling Jupiter o this discovery broke the Ptolemaic notion that things orbited because they avoid the tainted earthGalileoCatholic Churchchurch apposed to science o Church preserved greek science o Many earth scientists were churchmenChurch insisted on GEOCENTRIC universeHeliocentric universe promoted by Copernicusa monk1616 church banned heretical teachings as TRUE1623 gaileo published the Assayer1632 Galileo pulished famous book dialogues concerning Two Chief World Systemsput on house arrest for his life dies in 1642Johannes Kelpergerman improved on Copernicus said planets move on slightly eccentric ellipses not perfect circles around the sunMade observations of the planets with high accuracy with no epicyclesFall of Ptolemaic System Sir Isaac Newton said that all bodies exerted gravitational forced proportional to their mass and inversely proportional to the square of the distances between themTheory predicted that elliptical orbits centred on the Sun for planetsNetwons law of motion also explained how the earth could move with no wind air simply moves along with the earthDue to this Heliocentric system was vindicated provedNewtons theory of gravity said that all bodies in the solar system had gravity and were similar some howStars were not bodies of ordinary matter o Galileos telescope could revewal previously unseen detailed on planets but nothing but light for stars o Earth moved around sun stars should undergo motion called parallaxParallaxonly way to measure astronomical distances to early scientists stars appear slightly shifted from different positions of the earth on its orbit farther away the star is the smaller the parallax angle P1 parsec326 light years1 light yeardistance light travels in 1 year9 x 102d3600pdin parsec pin degrees1 arcsecond of movement1 parsec awayarcsecond circle has 360 degrees 1 degree60 min of arc 1 arcminute 1 arcminute60 seconds of arc 1arcsecond1 arcsecond11296000 of a circle very small
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