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8Sci CH20

8th Science CH20 Stars and Galaxies

TermDefinition
galaxy elliptical, spiral, or irregular shaped groups of stars, dust, and gas held together by gravity and grouped into clusters; Earth belongs to the Milky Way galaxy which contains about 200,000 stars
light-year distance light travels in one year; a light-year is the unit astronomers use to measure distances in space, 1 light-year is about 9.5 trillion kilometers
nebula large cloud of dust and gas whose particles exert a gravitational force on each other, causing the cloud to contract and its internal temperature to rise until fusion betins, resulting in a star being born
star glowing, hot sphere of gas, such as the sun, whose brightness depends on how big and hot it is and its distance from Earth; stars form from nebulas and produce energy by fusion; types of stars include blue supergiants, brown dwarfs, and red giants
sunspot cool, dark areas on the surface of the sun that may appear and disappear over days or months; years in which there are many large sunspots are called sunspot maximums , which occur about every 11 years
supernova explosion of a massive, dense-cored star that occurs when no more material remains in the core to be transformed, resulting in the formation of a small neutron star