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Astronomy & Astrophysics
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Chapter 1 11/16/2011 8:32:00 AM Chapter 1: What is our place in the universe?  Geocentric: Earth-centered universe  Solar system: the planets and their moons, and countless smaller objects including rocky asteroids and icy comets  Galaxy: a great island of stars in space, containing from a few hundred to a trillion or more stars  Galaxy clusters: groups od galaxies with more than a few dozen members  Supercluster: regions in which galaxies and galaxy clusters are most tightly packed (clusters of galaxy clusters)  Universe: the sum total of all matter and energy, encompassing the superclusters and voids and everything within them  Universe is expanding at a decreasing acceleration rate The Big Bang and Expanding Universe  Big Bang: when the expansion of the universe began (14.4 billion years ago)  Galaxies/ galaxy clusters occur where gravity was stronger than the expanding force of the universe Stellar lives and galactic recycling  Gravity causes clouds of gas and dust to collapse and form stars and plants  A star is created due to nuclear fusion; gravity compresses the material in a cloud to the point where the centre is dense enough and hot enough to generate energy by nuclear fusion  A stars life span only lasts as long as it can shine with the energy from the fusion  When a star runs out of energy and "dies", it explodes and most of its content is blow out into space  Supernova: the explosion of a dying star  New stars are born when the matter from older stars floating around in the galaxy form new clouds of dust and gas Stars manufactured the elements of earth and life  The early universe only contained hydrogen and helium  The other elements that exists today were created by stars (nuclear fusion and supernovae) How can we know what the universe was like in the past?  By studying light from distant stars and galaxies we can see into the past  "The farther away we look in distance, the further back we look in time."  And picture we see of galaxies is a shot of both space AND time  14.4 billion light years is the boundary of our potential observation How is earth moving in out solar system?  The Earth rotates daily and orbits the sun annually  Rotates from west to east (counter-clockwise as seen from above the North Pole)  Earths average orbital distance = 1AU (150milliom km)  Ecliptic plane: earths orbital path (flat plane) How is our solar system moving in the Milky Way Galaxy?  Stars @ diff. distances from the galactic centre orbit @ diff. speeds o We can use these speeds to determine how mass is distributed in the galaxy  Halo: the area of a galaxy outside its visible disk, where the mass of the galaxy is located (made up of dark matter)  Dark matter: matter from which no light is emitted/ reflected o Galaxies are made mostly of dark matter o Significantly outweighs regular matter that planets and stars are made of Are we ever sitting still?  Our galaxy is constantly moving among the galaxies of our local group, while all other galaxies move away from us in the expanding universe How has the study of astronomy affected human history?  Copernican revolution(1543): showed that Earth is not the centre of the universe, but instead, Earth revolved around the sun o This was later justified further by Tycho Brahe, Johannes Kepler, and Galileo Galilean Moons 11/16/2011 8:32:00 AM - Galilean moons discovered by Galileo - He was very famous because he was the first man to
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