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Term Definition
Cassegrain telescope

A type of reflecting telescope whose eyepiece is located behind the primary mirror. The primary mirror is cast with a hole in the center. When light enters the telescope, it reflects from the primary mirror to the secondary mirror. The secondary mirror reflects the light back through the hole in the primary mirror to the eyepiece.

Celestial pole

The north and south celestial poles are points on the celestial sphere where earths axis of rotation intersects the celestial sphere.


A pulsating variable star, undergoes a rhythmic pulsation as indicated by its regular pattern of changing brightness as a function of time. The period of pulsation has been demonstrated to be directly related to a Cepheid's intrinsic brightness.


Chunk of frozen gasses, ice, and rocky debris that orbits the Sun. As the nucleus begins to disintegrate, it also produces a dust tail in its orbital path and a gas or ion tail pointing away from the Sun.

Computer Hand Control
מחשב הטלסקופ – שלט המאפשר שליטה ובחירת מטרות הצפייה

A grouping of stars that make an imaginary characters in the sky. There are 88 constellations.

Cosmic Ray

Atomic nuclei (mostly protons) which observed to strike the Earth's atmosphere with extremely high amounts of energy. Cosmic Rays sometimes hit the telescope's CCD camera which may leave a trails on the final image.