Monday, April 2, 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. However, you know - but your ancestors didn't know - that the earth rotates about its polar axis from west to east once in 24 hours. The way in which these apparent movements occur depend on where you are situated on the earth's surface. On the other hand, for a person standing at one of the poles, the horizon coincides with the celestial equator, and it would appear that half the sky, i. , the part above the horizon, is turning about the pole - clockwise at the north pole, and anti-clockwise at the south pole. The height of the pole in degrees corresponds to the observers latitude. Then the celestial south pole would be located 30 degrees above your southern horizon. Of course, the same would apply if you found yourself in the northern hemisphere. A person who is familiar with the night sky would know that any given star appears to rise about four minutes earlier every night as seen from a particular place on Earth. It is this motion that changes our vantage point with respect to the background stars. . WHAT'S UP  

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