z Astronomy Exam 3 Comprehensive Study Guide Created by Gregory Galmin Chapter 16 Atomic emission each has its own fingerprint in the form of a spectrum of color that it absorbs and a spectrum in which it emits It s like a bar code for atoms Rotational period of a star you can tell by the Doppler effect The spectrum of a quickly rotating star is different than that of a slower rotating star Stellar parallax you can tell by the amount of arc seconds a star moves relative to background stars over the course of some time period For example If in six months a star moves 1 arc second relative to the background stars the star is 3 26 light years away or one parsec Remember Han Solo Hertzsprung Russel diagram shows how the temperature of a star is related to its brightness Is the star moving towards us or away from us If something is red shifted that means it s moving away from us The opposite is blue shift If the Ca spectrum of a star is red shifted 10nm from 500nm z is the change in wavelength divided by the actual wavelength v is the velocity speed and c is the speed of light V 5 940 000m s Chapter 17 The sun is mostly hydrogen and helium There s a lot more hydrogen than helium though Internal structure of the sun The core it is like 10 million degrees This is where nuclear fusion of hydrogen into helium happens Radiative zone This is where the energy produced in the core is radiated out in the form of photons and heat Convective zone The layer where heat is carried outward Photosphere This is the visible surface of the sun About 6000K Chromosphere Less dense than the photosphere This is visible during solar eclipses This is several thousand degrees hotter than the surface of the sun It is violet Solar transition this is the area between the chromosphere and the solar corona where the temperature spikes to millions of degrees Solar corona It is a billion times less dense than the photosphere This is where the solar wind comes from It is made of plasma Solar wind these are ions that are no longer gravitationally bound to the sun and they shoot off into space Granules these are convective bubbles Super granules these are bigger granules tens of thousands of kilometers across z 1 2 1 z 1 2 1c v The colors of the layers correspond to blackbody radiation The hotter something is the bluer it will be Our sun s photosphere is yellow because it is about 6000K Humans emit light in the infrared because we are not that hot Some things are so hot that they only give off X Ray light Sun spots these are intense concentrations of magnetism They are dark because they are cooler relative to their surroundings They occur in pairs because they are the each the end of a magnetic field loop They occur around the equator of the sun because the magnetic field of the sun is extremely distorted and at a great level of distortion sunspots are forms This is a cycle that happens about every 11 years Differential rotation of the sun the equator and areas near the poles rotate around the sun at different speeds Sun s energy it comes from high temperature nuclear fusion in the core Sun flares aka Solar flares this is when magnetic energy in the solar atmosphere is released in the form of electromagnetic waves Prominences are especially large solar flares Chapter 18 Solar systems are formed from nebulas which are molecular clouds that are extremely thin and can be light years across They are mostly made of hydrogen and helium Evidence for stars forming in dark interstellar clouds we take snapshots at different places in the universe that show the steps of star formation Density fluctuations cause the collapse of interstellar clouds Things that are denser can use gravity to attract more mass to become even more massive Protostars An accretion disk of Hydrogen and helium collapse into a single mass and when the mass reaches 20000K it is considered a protostar What stops a protostar from growing even more is its solar wind blows away the accretion disk Main sequence stars they are sorted by luminosity and color Protostars get their energy from infalling matter Main sequence stars get their energy from nuclear fusion Planet formation rings condense around the protostar and when they cool off protoplanets form You expect to finder denser more rocky material near the sun and more gaseous materials the farther you go away from the sun This is because denser materials sink more towards the center of gravity the center of gravity being the sun Chapters 19 and 20 HR diagrams show the different phases of a star a main sequence star will become a red giant at some point in its life Stellar evolution Stars begin their life in as nebulas which become a solar systems composed of protostars and protoplanets Once the star becomes large enough it will become a main sequence star fusing hydrogen into helium The hotter the core of the star the heavier the elements it can fuse A star usually spends billions of years in the main sequence phase When the fuel at the core runs out the star becomes a red giant then a planetary nebula then and a white dwarf This is the path followed by stars that are about the same mass as the sun A star s lifetime depends greatly upon its mass The more massive the star the shorter the lifetime Bigger stars tend to explode into supernovae Supernova this is when a star explodes and sends out all of its material this is where the heaviest elements are made Neutron star it is the result of a collapsed star after a supernova It is made completely out of neutrons and a teaspoon of it would weigh as much as a huge mountain White dwarf they are the remnants of the collapse of a main sequence star They are very dense and about the size of the earth Their energy comes from leftover thermal energy Black hole a thing that is so dense and gravity is so much that not even light can escape from it They are formed when a large star runs out of fuel and collapses under its own gravity Schwartzchild radius the radius of a sphere that is so dense that its escape velocity is the speed of light this is the definition of a black hole Let s say a star 11 times more massive than the sun became a black hole its Schwartzchild radius would be G is the gravitational constant m is the mass of the black hole and c is the speed of light in a vacuum You just plug it in The mass of the sun will be given on the exam Main sequence stars are alike because the pressure from the inside of the star is equal to the gravity of the star They