8-28 notes - Recap In 18th 19th centuries galaxies were known as island universes Study of universe is cosmology Big Bang occurred about 13.7 billion

8-28 notes - Recap In 18th 19th centuries galaxies were...

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Recap In 18 th , 19 th centuries galaxies were known as “island universes” Study of universe is cosmology Big Bang occurred about 13.7 billion years ago Universe is still expanding today Local Group has 20 galaxies (but close to 40?) Astronomers defined average distance to the Sun as the Astronomical Unit to measure distances Distance to Mercury - .4 AU Distance to Venus - .7 AU Distance to Mars - 1.5 AU Distance to Jupiter - 5 AU New Notes Now we know 1 AU is about 93 million miles Radar signals and timing are used today to measure planetary distances Speed of light – 186,000 mi/sec Light-year – distance light travels in a year Light takes 8 minutes to travel 1 AU/93 million miles/from Sun to Earth Next-nearest star (other than the Sun) is 4.5 light-years away Next-nearest galaxy (Andromeda) is 2 million light-years away If you look far enough back (13.7 billion light years away) you can technically still see light from the Big Bang Radius of the Earth is 4000 miles

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