1 Astronomical Distances • 1 meter (m) = 39.4 in = 1.1 yard • 1 kilometer (km) = 1000 m = 0.6 mile • 1 astronomical unit (AU) = 150,000,000 km = average distance between Earth & Sun • 1 light year (ly) = 9,500,000,000,000 km = distance light travels in a year Our Place in Space • Earth: rocky planet with iron core • Sun: typical star – ball of hot gas, mostly hydrogen & helium • Sun is 100x larger in diameter than Earth • Volume of Sun is 1,000,000 times volume of Earth • Earth-Sun distance: = 1 AU = 100 x Sun’s diameter = 10,000 x Earth’s diameter Beyond the Solar System • Milky Way Galaxy – about 100,000 ly across – contains about 100 billion stars Sirius is very light because of the sun. They are very cl clcclosePolaris---North Stariron is denser than rock. Jupiter is made of Hydra andHand helium-also contains gas and dust clouds from which new stars formstars form.Clusters of galaxies-up to 10 million ly across-contain up to several thousand galaxies2 The Scientific Method • Scientific Theory – an idea that proposes to explain observations – scientific theories make testable predictions Constellations • Apparent groupings of bright stars on sky • Stars in constellations are usually at large range of distances Orion = Great Hunter • Sky appears to rotate counterclockwise daily about Polaris, the North Star • Due to Earth’s daily rotation from W to E Daily “Motion” of Sky N W E -If a theory is not consistent with new observationit is modified or discardedObserve, theorize, predict, test, modifyStars in constellations are usually not physically associatedassociatedAstronomical definition: constellation = sky regionSky is divided into 88 constellationsCauses most celestial objects to rise in E and set in WHow was this picture taken?Camera shutter was kept open for a long time..About 1/6 day = 4 hours3 Using your Sky Chart • Relation to Sky – chart shows visible sky at one time – outer circle is horizon • Orientation – always turn the chart so that direction on the bottom is same as the direction you are facing Polaris & the Dippers • Face north and turn chart so north is at bottom • Find the Big Dipper in the northeast pointers Polaris N NE pointers Polaris N NE • The Little Dipper is now below Polaris • Check back a few hours later – how has the sky changed? pointers Dot sizes are proportional to apparent stellarbrightnessConstellations are shown as dotted linesFollow "pointer starts" to Polaris, the "North star"Big Dipper is part of Ursa Major = big bearPolaris is at end of handle of Little Dipper = UrsaMinor = little bearRotated counterclockwise about Polaris4 The Constellation Orion • the Great Hunter • brightest winter constellation • now high in south in evening • Contains: Annual Constellation Cycle • Cannot see stars on side of sky containing Sun • Only see stars located on side of sky opposite from Sun, i.e. on night side of Earth • as Earth orbits Sun, different constellations become visible Fig 1-14a Astronomy vs. Astrology • Astrology is an ancient superstition not based on the scientific method – is not tested by observation or experiment - Betelgeuse: Red supergiant- Orion Nebula: Region of very active star formation- Rigel: blue supergiantZodiac- As seen from Earth, Sun appears to move around sky once per yeasky once per year, relative to stars-traditional: 12 constellations located along Sun'sapparent path-Sun spends 1 month in each oneAstronomy is a modern science- based on the laws of physics-verified by observation and