CAS AS 101 Lecture Notes - Lecture 3: Orbital Speed, Observable Universe
25 Jan 2018
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Document Summary
Astronomical unit (au): earth"s average distance from the sun. Used to describe distances within our solar system. 1 light-year (ly): distance covered by light in 1 year. ~10 trillion km or 6 trillion mi. Used to describe distances of stars and galaxies. Light travels at finite peed (300,000 km/s) could circle earth 8 times / sec. Thus, we see objects as they were in the past: the farther away we look in distance, the further back we look in time. At great distances, we see objects as they were when the universe was much younger. Size of the entire universe can be more but not the age, which is 14 billion years -> 14 billion-light years size of our observable universe. Answer: because looking 15 billion light-years away means looking to a time before the universe existed. Shape of the galaxies become more blurry as it gets farther away in distance.
