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Parabolic Mirror
A parabolic or more accurately a "paraboloidal" mirror, is ground to a shape which brings all incoming light rays to a perfect focus, on axis.
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Planetary Nebula
A circular or oblong region of gas that has been thrown off by a central star. Its name comes from its apparent similarity to the disk of a planet seen in a very small telescope.
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Polar Axis
A telescope mount's axis that is parallel with the earth's axis. With a drive motor, the motion of stars due to the earth's movement can be counteracted so that they remain in the field.
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Power
See Magnifying Power.
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Prime Focus
The focal point of the objective mirror or lens.
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