Astronomy Week 1 Readings: 1.1-1.4

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Astronomy & Astrophysics
Michael Reid

1. Our place in the universe 9/17/2012 6:13:00 PM 1.1 Our modern view of the universe  We live in an Earth-centered (geocentric) universe  Different theories explaining space/earth but slowly evolved to what we know today (earth is flat, sun-centered, etc) What is our place in the universe?  Planet in the solar system (consists of Sun and all objects that orbit it like planets, stars, moons, asteroids and comets)  Sun = just 1 star in huge collection of stars called the Milky Way Galaxy  Galaxy = great island of stars in space (trillion stars)  Galaxy clusters = group of galaxies w/more than a few dozen members  Superclusters = galaxies/group of galaxy clusters tightly packed  Universe = the sum total of all matter and energy, encompassing the superclusters and voids and everything within How did we come to be?  Humans are newcomers in an old universe  The Big Bang and the Expanding Universe o Entire universe is expanding = average distances b/w galaxies are increasing with time  Galaxies must have been closer in the past o The beginning = Big Bang (14 billion years ago) o While universe expands, ind. galaxies/galaxy clusters don‟t  Stellar Lives and Galactic Recycling o Gravity drives collapse of clouds of gas + dust to form stars/planets, which go through “life cycles”  It‟s born (nuclear fusion) -> lives as long as it can shine w/energy from fusion -> dies -> supernovae (blows up content back into space) -> mixes w/other matter in space -> becomes part of new clouds of gas/dust and is reborn = Cosmic recycling plants  Stars Manufacture the Elements of Earth and Life o Early universe contained only hydrogen and helium (trace of lithium) but earth is made of carbon, nitrogen, oxygen, and iron  Other elements were manufactured by stars (through nuclear fusion or nuclear reactions) o Cloud that gave breath to our solar system = 98% helium and hydrogen and 2% other elements (which helped make Earth sustainable for life) How can we know what the universe was like in the past?  By studying light from distant stars/galaxies  Light travels extremely fast (circle Earth 8x in a second) so we measure distance to the stars in units called light-years  “The farther away we look in the distance, the further back we look into time” o If star is 8 light-years away, it look 8 years for that light to come to us, meaning we don‟t see that star as it is today but rather what it was 8 years ago Can we see the entire universe?  Universe = 14 billion years old + we are always seeing things far back in time when looking at space so it places limit on the portion of the universe we can see o Looking back at star 12 billion light-years away, we see it was when the Earth was only 2 billion years old  The distance for 14 billion light-years, therefore, marks the boundary of our observable universe (portion of the universe that we can potentially observe) 1.2 The scale of the universe How big is Earth compared to our solar system?  Sun is the largest, way larger than any of the planets  Jupiter is the largest planet  Moon is close to earth  Mars is more than 150x as far as a trip to the moon  Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune (Pluto + Eris = dwarf planets) How far away are the stars?  Large distances between stars give perspective on technological challenges in astronomy  Takes years and years from one point to another (distance teaches lesson on interstellar travel as well) How big is the Milky Way
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