Chapter+13

=Stars= __Constellations__ - Patterns of stars in the night sky. Some Modern constellations: -Ursa Minor -Ursa Major -Orion -More.. but all circle around the north star, Polaris. __Absolute Magnitude__ - a measure of the amount of light a star gives off. __Apparent Magnitude__ - a measure of the amount of light received on earth. __Light-year__ - the distance that the light travels in one year. (300,000 km/s, or about 9.5 trillion km/year) __Star temperature color__: Hotter stars - blue-white color Cooler stars - orange or red color =Sun= __Sun's Atmosphere__ __Sunspots__ - Areas of the sun's surface that appear dark because they are cooler than the surrounding areas. __Prominences and Flares__ Prominences - huge, arching columns of gases. Flares - gases near sunspots sometimes brighten suddenly, shooting violently outward at high speed. Flare: ** __CEMs__ - Coronal mass ejections (CEMs) occur when large amounts of electrically-charged gas are ejected suddenly from the sun's corona. Can occur up to two-three times a day during a sunspots maximum. Little danger to earth life, but cause problems: -can damage satellites -interfere with radio and power distribution equipment -cause auroras =Evolution of Stars= __Main Sequence__ About 90% of all stars are main sequence stars. __Nebula__ - a large cloud of gas and dust in which stars are formed. __Giant__ - when hydrogen in the core of the star is depleted, a balance of pressure and gravity no longer exists. The core contracts, the temperature inside the star increases. This cause the outer layers to expand and cool. __White Dwarf__ - after a star's core uses much of its helium, it contracts even more and its outer layers escape into space. __Supergiant__ - in massive stars, the core heats up to much higher temperatures. Heavier and heavier elements form by fusion, and the star expands. Can form iron in its atomic structure which can cause it to collapse violently, and a shock wave travels outward through the star. The outer portion of the star explodes and creates a __supernova__. __Neutron star__ - when a star shrinks to a size about 20 km in diameter and only neutrons can exist in the dense core. __Black hole__ - when gravity near a mass more than three times more massive than the sun, nothing can escape from it. =Galaxies and the Universe= __Galaxy__ - a large group of stars, gas, and dust held together by gravity. __Spiral Galaxies__ - galaxies that have spiral arms that wind outward from the center. __Elliptical Galaxies__ - galaxies shaped like large, three-dimensional ellipses. __ Irregular Galaxies__ - galaxies that have many different shapes.
 * Prominence: