# Chapter 1-5 - Chapter 1 1 Most of human history ancestors...

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Chapter 1: 1. Most of human history, ancestors thought that earth was stationary at the center and the universe was relatively small a. Geocentric: the idea that earth is the center of everything b. Cosmic Address: local supercluster, local group, milky way galaxy, solar system, earth c. Solar system: con s ists of the sun, the planets, and their mon s d. Galazy: great island of stars in space, all held together by gravity e. Local group: groups of galaxies with many more large members often called galazy clusters f. Superclusters: regions where galaxies and galaxy clusters are more tightly packed g. Universe: all of the above make up our universe h. Astronomical units: earths average distance from the sun (about 150 million km) i. Light-year: the distance that light can travel in one year i. Unit of distance and not time ii. Takes roughly one second for light to travel from the moon to earth iii. 8 minutes for light to travel from the sun to the earth 1. The farther away we look in distance, the further back in time we are looking j. Observable universe: i. 14 billion years ago is when our universe was created and if we try and look at something which would take more than 14 billion years to reach us then we would see nothing ii. The boundaries of the observable universe is 14 billion years iii. There are as many stars in the observable universe as there are grains of sand on all the beaches on earth k. Scale of the solar system: i. On a scale in which the sun is the size of a grapefruit, earth is the size of a ballpoint from a point which orbits the sun at a distance of 15 meters. l. Distance to stars: i. Nearest star to our own is alpha centauri 2. History of the Universe: a. Big bang: i. The earth is expanding 1. Meaning the average distances between galacies are increasing with time 2. The point where the galaxies began expanding which is the big banmg b. Stallr lives and galactic recycling: i. Gravity drivs the collapse of clouds of gas and dust to form stars and planets

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ii. Nuclear fusion: a star is born when gravity compresses the material in a
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