Chapter 1 A Modern View of the Universe 01 26 2014 1 1 The Scale of the Universe Our Cosmic Address Solar System consists of the sun the planets and their moons and countless smaller objects that include asteroids and icy comets Galaxy great island of stars in space containing between a few million and a trillion or more stars o Milky Way Galaxy disk shaped collection of stars that our solar system belongs to It contains more than 1000 billion stars our solar system is located a little over halfway from the galactic center to the edge of the galactic disk Galaxy Clusters groups of galaxies with more than a few dozen members are often called galaxy clusters o Local Group group of galaxies Milky Way is one of the two largest among the 40 galaxies in the Local Group Superclusters clusters of galaxy clusters The regions in which galaxies and galaxy clusters are most tightly packed are called superclusters Our Local Group is located in the outskirts of the Local Superclusters Universe the universe is the sum total of all matter and energy encompassing the superclusters and voids and everything within them Astronomical Distance Measurements Astronomical Unit AU we commonly describe distances within our solar system in astronomical unites Earth s average distance from the sun which is about 150 million kilometers 93 miles Lightyear ly we generally use lightyears to describe the distances of the stars and galaxies Distance that the light can travel in one year which is about 10 trillion kilometers 6 trillion miles o Lightyear is a unit of distance not of time Light travels at the speed of light which is 300 000 kilometers per second Looking Back in Time The speed of light could circle Earth nearly 8 times in a single second 1 second to reach Earth from Moon 8 minutes to reach Earth from the Sun Stars are so far away that their light takes years to reach us which is why we measure their distance in lightyears o The father away we look in distanced he further back we look in time Siruis brightest star in the night sky is located about 8 lightyears away Orion Nebula giant cloud in which stars and planets are forming is located about 1 500 lightyears from Earth Andromeda Galaxy is about 2 5 million lightyears away o When we study the universe it is impossible to separate space and time The Observable Universe Observable Universe the portion of the entire universe that we can potentially observe The distance of 14 billion lightyears therefore marks the boundary or horizon of our observable universe sand in the world o The total number of stars in the universe is comparable to number of grains of The Scale of the Solar System The Voyage Model located in Washington D C show shte Sun and the planets between them at one ten billionth of their actual sizes and distances o Sun grape fruit size The sun is far larger than any of the plants In mass the sun outweighs all the planets combined my a factor of nearly 1 000 o Earth ball point size located 15 meters 16 5 yards away from the sun o Solar System kilometer on a side an area equivalent to more than 300 football fields arranged in a grid Distance to the Stars Alpha Centauri the nearest star system our own a three stare system called Alpha Centauri about 4 4 lightyears away The Voyager 2 spacecraft traveling at a speed of 500 000 kilometers per our about 100 times as fast as a speeding bullet would take about 100 000 years to reach Alpha Centauri if it were headed in that direction 1 2 The History of the Universe The Big Bang Expansion and the Age of the Universe Big Bang 14 billion years ago point at which the expansion began Expansion implies that galaxies must have been closer together in the past and if we go back far enough we must reach a point of the beginning Expansion Telescopic observation of distant galaxies show that the entire universe is expanding meaning that the average distances between galaxies are increasing with time o While the universe is expanding the individual galaxies and galaxy clusters and objects within them such as stars and planets do not expand Stellar Lives and Galactic Recycling Nuclear fusion a star is born when gravity compresses the material in a could to the point at which the center becomes dense enough and hot enough to generate energy by nuclear fusion It is the process in which light weight atomic nuclei smash together and stick or fuse to make heavier nuclei Recycling the star lives as long as it can shine with energy from fusion and dies when it exhausts its usable fuel In its final death throes a star blows much of its content back out into space The returned matter mixes with other matter floating between the stars in the galaxy eventually becoming part of new clouds of gas and dust which generation of stars can be born o Galaxies are therefore function as cosmic recycling plants recycling material expelled from dying stars into new generation of stars and planets o Supernovae most massive stars die in titanic explosions Star Stuff Early universe contained only the simplest chemical elements hydrogen and helium By the time our solar system formed 4 5 billion years ago earlier generations of stars had already converted about 2 of our galaxy s original hydrogen and helium into a trace of lithium heavier elements o Therefore the cloud that gave birth to our solar system was made of about 98 hydrogen and helium and 2 other elements Carl Sagan we are Star Stuff most of the material from which we and our planet are made was created inside stars that lived and died before the birth of our Sun January 1 The Bing Bang Cosmic Calendar February The Milky Way forms September 3 Earth forms September 22 Early life on Earth December 17 Cambrian explosion December 26 rise of the dinosaurs December 30 extinction of the dinosaurs December 31 early hominids human ancestors began to walk upright o 11 seconds before Ancient Egyptians built the pyramids o 1 second ago Kepler and Galileo proved that Earth orbits the Sun rather than vice versa 1 3 Spaceship Earth Rotation and Orbit Rotation Earth rotates once each day around its axis which is the imaginary line connecting the North Pole and the South Pole o Earth rotates from west to east counterclockwise as viewed from above the North Pole which is why the Sun and stars appear to rise in the east and set o Speed of more than 1 000 kilometers per hour 600 miles per hour faster than in the west each day most airplanes travel Orbit at the same time as it is rotating Earth also