chap 1 and 2 - O ur Place In space Earth 1 planet of 8 Sun...

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Our Place In space… Earth – 1 planet of 8 Sun – an ordinary star. One of 100 billion in our galaxy the “Milky way” Milky Way – typical galaxy, one of 10s or 100s of billions of galaxy in observable universe The scale of thins Solar system :all 8 planets lie within about 40 astronomical units. 1 AU is about 150 million km Distance between stars often measured in light years Speed of light = 300,000 km/s = 9.46 trillion km/yr 1 light year = 9.46 trillion km (5.88 trillion miles) Our galaxy is about 100.00 ly across How can we know what the universe was like in the past? Light travels at a finite speed Moon light travel time 1 second Sun light travel time 8 minutes Sirius light travel time 8 years Andromeda Galaxy light travel time 2.5 million years Thus we see objects as they were in the past. The farther away we look in distance the further back we look in time.
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How is Earth moving in our solar system Contrary to our perception we are not sitting still. We are moving with the Earth in several ways and at surprisingly fast speeds. Earth rotates on its axis Earth orbits the sun (revolves) once every year At an average distance of 1AU With earths axis tilted by 23.5 degrees ( pointing to Polaris) And rotates in the same direction counter clockwise Our sun moves randomly relatively to the other stars in the local solar neighborhood At typical relative speeds of more than 70.000 km/hr But stars are so far away that we cannot easily notice their motion And it orbits the galaxy every 230 million years Most of Milky Ways light comes from disk and bulge, but most of the mass is in its halo How do galaxies move within the universe Galaxies are carried along with the expansion of the universe. But how did hubble figure out that the universe is expanding All galaxies outside our local group are moving away from this The more distant the glalaxy, the faster it is racing away The Milky Way Our galaxy is shaped like a disk The local sky An objects altitude (above horizon) and direction (along horizon) Zenith – the point directly overhead
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Horizon – all points 90 degrees away from zenith The meridian is an imaginary half- circle stretching from the horizon due south, through the zenith, to the horizon due north. Angular Measurments Full circle = 360 1 degree= 60’ (arcminute) 1’=60’’ (arcseconds) Daily Motion As the earth rotates, the sky appears to rotate in the opposite direction The sky appears to rotate N (or S) celestial poles If standing at poles nothing rises or sets If standing at equator everything set 90 degrees to the horizon The altitude of the celestial pole = (your latitude) All stars at an angle < Your latitude away from : Your celestial pole – never set (circumpolar) The other celestial pole are never seen Other stars and sun moon and planets rise in east and set in west at an angle = 90 degrees – your latitude Why do constellations we see depend on latitude and time of year? They depend on latitude because your position on earth determines which constellations
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This note was uploaded on 03/10/2010 for the course ED 4070 taught by Professor Sweet during the Fall '09 term at Western Michigan.

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chap 1 and 2 - O ur Place In space Earth 1 planet of 8 Sun...

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