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Chapter 1 Stars and Galaxies Binary star- member of a double star system Constellation- group of stars that form a pattern Nova- star that suddenly increases in brightness in just a few hours or days Nebula- massive cloud of dust and gas between the stars Galaxy- huge collection of stars Spiral Galaxy- galaxy that is shaped like a pin wheel; one of the three types of galaxies Elliptical galaxy- galaxy that may vary in shape from nearly spherical to flat; one of three types of galaxies Spectroscope- instrument that breaks up the light from a distant star into its characteristic colors Spectrum- band of colors formed when light passes through a prism Red shift- shift toward the red end of the spectrum of a star that is moving away from the Earth Doppler effect- apparent change in the wavelength of light that occurs when an object is moving toward or away from the Earth Big-bang theory- theory that states that the universe began to expand with the explosion of concentrated matter and energy and has been expanding ever since Gravity- force of attraction between objects Quasar- quasi-stellar radio source; distant object that gives off mainly radio waves and Xrays Giant star- star with a diameter about 10 to 100 times as large as the sun Supergiant star- star with a diameter up to 1000 times the diameter of the sun; largest of all stars White dwarf- small dense star Neutron star- smallest of all stars Apparent magnitude- brightness of a star as it appears from Earth Absolute magnitude- amount of light a star actually gives off. Hertzsprung-Russell diagram- chart that shows the relationship between the absolute magnitude and the surface temperature of stars; also called H-R diagram Main-sequence star- star that falls in an area from the upper left corner to the lower right corner of the H-R diagram Parallax- apparent change in the position of a star in the sky due to the change in Earth’s position as the Earth moves around the sun Nuclear fusion- process by which hydrogen atoms are fused, or joined together, to form helium atoms Corona- outermost layer of the sun’s atmosphere Chromosphere- middle layer of the sun’s atmosphere Photosphere- innermost layer of the sun’s atmosphere Core- center of the sun Prominence- violent storm on the sun that can be seen from Earth as a huge bright arch or loop of hot gas Solar flare- storm on the sun that shows up as a bright burst of light on the sun’s surface Solar wind- continuous stream of high-energy particles released into space in all directions from the sun’s corona Sunspot- dark area on the sun’s surface Axis- imaginary vertical line through the center of body around which the body rotates, or spins Protostar- new star Supernova- tremendous explosion in which a star breaks apart, releasing energy and newly formed elements Pulsar- neutron star that gives off pulses of radio waves Black hole- core of a super-massive star that remains after a supernova; the gravity of the core is so strong that not even light can escape