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Understanding the Celestial Coordinate System, Continued
To help you visualize the celestial coordinate system, always imagine
Earth at the center of the celestial sphere. These facts and figure 6-2
should help you visualize the celestial coordinate system.
Facts
The first point of Aries is the starting point for all celestial
observations.
Celestial bodies are in constant motion (that’s why it was stressed in
chapter 5 that the exact time of a celestial observation must be
recorded).
The use of GHA associates all hour circles of any celestial body with
the Greenwich meridian on Earth. This allows all celestial bodies to
be positioned at any moment on the celestial sphere.
The GHA of Aries will align Aries with the Greenwich meridian.
Figure 6-2. The celestial coordinate system.
6-4
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