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AST study

# AST study - Angular measurements we talk about things in...

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Angular measurements- we talk about things in angular size - 1 degree= 60 arc minutes 1 arc minute= 60 arc seconds (more useful for things so tiny) - Diameter of moon is 1/2 degrees, same diameter of sun = lunar and solar eclipse because they appear the same size To convert degree and arcs to a physical measure or figure out how much energy something is giving off you need the distance Convert through Trig: tangent x = diameter/ distance 1 AU= 1 earth to sun distance... use in solar system 1 AU= 8 light minutes... use outside of solar system; generally used for distance between stars Light travels at 3.0x10^5 km/sec... nothing goes faster... allows us to “look back in time” earth rotates once on its axis every 23 hrs and 56 min, but it takes 4 min a day for earth to move around sun, solar day = sunset to sunrise 24 hrs sidereal day= star rise to star rise 23 hrs and 56 min Every 6 months the set of stars in the plain of the solar system rotates the north star (due north) is in the sky year round winter= sun is in the southern sky at -23 degrees summer= sun in norther sky at +23 degrees spring and fall when sun= 0 degrees Longitude goes from 0-360 east to west ..... right ascension Latitude goes from +90 to -90 north and south ..... declination Moon reflects the sun’s light and orbits around the Earth Lunar calendar is 29 days Magnitude measures brightness, each is 2.5 time fainter then the next Sun= -26 magnitude Faintest the human eye can see is magnitude 6= (2.5)^6 Numbers go up brightness goes down Depends on how far away a star is and how much energy the star gives off Luminosity= energy/second Twinkling depends on size, temperature, and air density... less atmosphere less distortion Strongest to weakest: 1) strong force (nuclear force), short range 2) weak force, short range 3) electromagnetic force (between + and -), long range force 4) gravity, long range (nothing cancels it out); not just a good idea, it’s a law Copernicus- geometrical model of the solar system - wanted only 1 set of circles since the ptolemaic system was not “pleasing to the mind” - found that it was explained well with sun at center - predicted Jupiter and Saturn conjunction by 10 days Success- simplified systems, provided a natural explanation for retrograde notation, and reveled a new order Failure- did not predict observations any better than old model

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Brache- accurate naked eye observations of planetary positions - showed heaven changed beyond moon; Nova 1572 -
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