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| | CLEA AstrometryLab |
 | | Two coordinates are all that is needed since the surface of the earth, the city map, and the sky, all appear two dimensional to the observer. |
 | | The coordinates that are commonly used to specify star positions in astronomy indicate the star’s position with respect to the celestial equator, an imaginary line in the sky that runs above the earth’s equator, and are therefore called the equatorial coordinate system. |
 | | For example, its equatorial coordi-nates measured in June, when the earth is at one side of the sun, will be different from its position in January when the earth is at the other side of the sun (see Figure 5). |
| www.mines.edu /Academic/courses/physics/phgn324/CLEA/Astrlab.html (7262 words) |
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