In: Physics
Answer:
Stellarium's celestial sphere is a concept for thinking about positions of objects in the sky. There are two different types of coordinate systems in the program. One type is altitude/azimuth coordinates. The Altitude/Azimuth coordinate system is used to describe a direction of view (azimuth angle) and height in the sky (altitude angle). The azimuth angle measures clockwise from due North. North is 0 degrees, East is 90 degrees, Southwest is 135 degrees, etc. The altitude angle measures up from the horizon. This means looking up (zenith) is 90 degree. Half way between the zenith and horizon is 45 degrees. The point completely opposite of the zenith is called the nadir. This type of coordinate system is good because it is intuitive. People know azimuth angles from navigation bearings. The altitude angle is also easy to visualize. This system is not good for describing general positions of stars because the values change with time and the observers location.
To draw the grid lines for this system in Stellarium press the button on the main tool bar or press [Z].
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