Thursday, May 31, 2012

"The Celestial Sphere - Astronomy's Model of the Apparently Changing Night Sky"

"The Celestial Sphere - Astronomy's Model of the Apparently Changing Night Sky"," To add to this confusion, printed star charts frequently show the sky as a circle, and in addition make reference to the cardinal points. The idea of a celestial sphere is not new. In our enlightened age we scoff at this idea, yet it remains a very useful model of the night sky. In order to grasp the concept of the celestial sphere, try to visualise an imaginary straight line that passes through Earth's north and south poles and extends to infinity at either end. Then the celestial north pole is located where this imaginary line extends from Earth's north pole and passes through the celestial sphere; the celestial south pole is on the opposite side. THIS IS HOW YOU DO IT","night sky","99%" "The Night Sky Zone"," It's as if we're inside of some great celestial (sky) sphere upon which the stars appear to be attached. In science we like to use models to illustrate abstract concepts. The International Astronomical Union officially designated a total of 88 constellations in the entire celestial sphere in 1930. A circular cardboard cutout looking like a star map freely rotating on a central pivot and connected to a square cardboard piece can be set to a time and day of the month while facing a certain direction. Recognizing stars and constellations is a good start, but locating much smaller, specific areas of the sky requires a detailed set of star charts. Lines representing streets and roads going north-south and east-west on our earth map can be turned into lines representing celestial coordinates on our sky map. These celestial lines of latitude north and south of the equator are now called lines of declination. Each degree can be further subdivided into 60 equal minutes (not time) of arc (part of the circle formed by the complete line) and each minute divided into 60 equal seconds (again, not time) of arc. One minute of arc at the Earth's celestial equator is approximately equal to one nautical mile on the earth. They measure hour angles increasing westward from 1 to 24 (0 and 24 are the same line) and are subdivided further into minutes and seconds of actual time. Equatorial mountings for telescopes can incorporate setting circles to manually align the instrument or use computers and motors to locate and track celestial objects. . WHAT'S UP


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