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AS101 (52)
Chapter 2

Astronomy Chapter 2.docx

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Arthur Read

Constellations—one of the stellar pattens identified by name, usually of mythological gods, people, animals, or objects. Also the region of the sky containing the pattern • Constellation boundaries were approximate, thus one star could be apart of 2 constellations • 88 official constellations • Constellation represents not a group of stars, but a boundary. All within the boundary belong to the constellation Asterisms—a named grouping of stars that is not a recognized constellation Magnitude Scale—the astronomical rightness scale. The larger the number, the fainter the star • Brightest stars are first magnitude, all the way to sixth magnitude—these stars are barely visible to the human eye • Hipparchus is believed to have compiuled the first star catalogue Appartent visual magnitude—a measure if the brightness of a star as seen by human eyes on earth Flux—a measure of the flow of energy out of a surface. Usually applied to light Celestial sphere—an imaginary sphere of very large radius surrounding Earth to which the planets, stars, sun, and moon seem to be attached Scientific model—a concept that helps you think about some aspect of nature without necessarily being true The Sky and Its Motions: • Sky objects aooear to rotate westward around earth each day, but that is because Earth is rotating east • What you can see of the sky depends where you are n Earth • Astronomers measure distances across the sky as angles expressed in units of degrees and subdivisions of degrees called arc minutes and arc seconds Precession—the slow change in orientation of the Earth’s axis of rotation. One cycle takes nearly 26,000 years Rotation—motion atround an axis passing through the rotating body Revolution—orbital motion about a point located outside of the orbiting body • Precession moves the poles The Cycle of the Sun: • The sky is filled with stars even in the daytime but glare of sun fills our sky with light • Through the year, the sun moves eastward on a line called the eliptic • Seasons are caused by the revolution of earth around the sun o Seasons are caused by changes in the amount of solar energy that Earth’s northern and southern h
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