Key Topics Astronomy Unit

Big Bang Theory Big Bang Theory: most widely accepted theory for the origin of our universe billion States that billion years ago, the universe was only a few millimeters across. According to this theory, the contents of the universe expanded explosively into existence about 13.7 billion years ago. expanded quickly expand After the big bang, the universe expanded quickly, and continues to expand, and cooled enough for atoms to form. Gravitygas clouds starsgalaxies Gravity pulled the atoms together into gas clouds that eventually became stars, which comprise young galaxies. History of the Universe

1.Galaxies appear to be moving away from us at speeds proportional to their distance. Hubble’s Law 1929 This is called Hubble’s Law, named after Edwin Hubble who discovered this phenomenon in This supports the expansion of the universe and suggests that it was once compacted. 2.If the universe was initially very hot as the big bang suggests, there should be remnants of this radiation Cosmic Background Radiation In 1965, Radioastronomers Arno Penzias and Robert Wilson discovered Cosmic Background Radiation, which supports the Big Bang. “light elements” Hydrogen and Helium 3.The abundance of “light elements” Hydrogen and Helium found in the universe is thought to support the Big Bang. Evidence of Big Bang Theory

Technology Technology provides the basis for many new discoveries related to space and the universe. telescopes Visual, radio, and x-ray telescopes collect info from across the entire electromagnetic spectrum. Computers Computers are used to manage data and complicated computations. Space probes Space probes send back data and materials from remote parts of the solar system. Accelerators Accelerators provide subatomic particle energies that simulate conditions in the stars and in the early history of the universe before stars formed. Technology and the Universe

galaxybillions gravity sizeshape light years A galaxy is a group of billions of individual stars, star systems, star clusters, dust and gas bound together by gravity. There are billions of galaxies in the universe, and they are classified by size and shape. They vary in size from a few thousand to a hundred thousand light years across. What is a Galaxy? A spiral galaxy

1.Elliptical Galaxies: 1.Elliptical Galaxies: round or oval in shape; some of the largest galaxies are elliptical galaxies. They are thought to be the most common type of galaxy in the nearby universe. 3 Types of Galaxies Elliptical Galaxy M87

2.Spiral Galaxies: 2.Spiral Galaxies: disc shaped galaxy that has a bulge in the middle; have spiral arms; makes up more than 50% of galaxies 3 Types of Galaxies (continued) Spiral Arm: contains gas and dust clouds and mainly hot, young stars Central bulge is packed with old red and yellow stars, which glow the brightest

3.Irregular Galaxies: 3.Irregular Galaxies: cannot be classified as elliptical or spiral; makes up about 3% of galaxies. 3 Types of Galaxies (continued) Irregular Galaxy

Milky Way Galaxy spiral Our solar system is part of the Milky Way Galaxy, which is a spiral galaxy. 100 billion stars 100,000 It has more than 100 billion stars and a diameter of more than 100,000 light years. center gas, dust, and most young stars At the center is a bulge of stars from which are spiral arms of gas, dust, and most young stars. Our Galaxy; The Milky Way

Hubble’s Law red shift speed distance Hubble’s Law states that galaxies which are farther away have a greater red shift, so the speed at which a galaxy is moving away is proportional to its distance from the Earth. Hubble’s Law

red shift Doppler red The red shift is a phenomenon due to Doppler shifting, so the shift of light from a galaxy to the red end of the spectrum indicates that the galaxy is moving farther away. expanding This is evidence for the Big Bang Theory because it tells us that the universe is still expanding sci.phys.fund.hubble2/hubbles-expanding- universe/ 03.sci.phys.fund.hubble2/hubbles-expanding- universe/ Hubble’s Law and the Red Shift

Early in the formation of the universe, stars coalesced out of clouds of hydrogen and helium and clumped together by gravitational attraction into galaxies. Early in the formation of the universe, stars coalesced out of clouds of hydrogen and helium and clumped together by gravitational attraction into galaxies. Stars

nuclear fusionmatter to energy When heated to a sufficiently high temperature by gravitational attraction, stars begin nuclear fusion, which converts matter to energy and fuse lighter elements into heavier ones. hydrogen helium All of the elements, except for hydrogen and helium, originated from the nuclear fusion reactions of stars. Stars

Stars are classified by: Color Color : from hottest to coldest: O (blue), B (blue), A (blue), F (blue to white), G (white to yellow), K (orange to red), M (red) Size Size Luminosity Luminosity: amount of energy released from the star; measured in Watts Mass Mass Classification of Stars

main sequence A star’s mass determines the star’s place on the main sequence and how long it will stay there. mass Patterns of stellar evolution are based on the mass of the star. collapse Stars begin to collapse as the core energy dissipates. Nuclear reactions expansion Nuclear reactions outside the core cause expansion of the star, eventually leading to the collapse of the star. Stars

Hertzprung-Russell sizes evolve A Hertzprung-Russell diagram is used to estimate the sizes of stars and predict how stars will evolve. main sequence left right Most stars fall on the main sequence of the H-R diagram, a diagonal band running from the bright hot stars on the upper left to the dim cool stars on the lower right. Hertzsprung-Russell Diagram

Hertzprung-Russell Diagram