Astronomy August 28, 2008 Lecture 2 • Difficulty to define the distance form earth to the sun. Astronomers came up with 1 AU (astronomical unit) from the earth to the sun. o Earth is in an elliptical orbit around the sun, so sometimes closer, sometimes further. 1 AU is the AVERAGE distance from earth to the sun. • Average distance to the sun is 93 million miles. o We wait and see when Venus is between us and the sun. Distance between earth and Venus is 3/10ths an astronomical unit. We bounce a radar signal towards Venus, hits Venus’ surface, then bounces back towards us. We simply time how long that takes, and we know the speed of light, and through that we can calculate how long the beam had traveled to Venus. • 186,000 miles per second is how fast light travels. • Light year is a measure of distance, not time. • Earth is traveling 65,000 miles an hour. In total, we’re moving 500,000 miles per hour (including orbiting around the galaxy). • Angular size of the moon- the angle it takes your arm to go from 1 side of the
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