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Sextant and octant were handheld instruments having a movable index arm that indicated the angle of elevation between a star the sun or moon and the horizon
the lens or system of lenses in a telescope or microscope that is nearest the object being viewed.
Moderns refractors avoid chromatic aberration by using special lenses consisting of two different kinds of glass cemented together
A telescope that uses both mirrors and correcting objective lens to gather light
In this form the light path enters the telescope through a special lens and then continues through a hole in the main mirror as with a standard cassegrainian
An instrument used to detect radio emissions from the sky, whether from natural celestial objects or from artificial satellites
Hubble space telescope
A special instrument that spans the optical and nonoptical categories of telescopes
The mathematical rule that relates the stretching of wavelengths of their light with increasing distances
Occasionally a star may increase it brightness by twenty magnitudes or more in an explosion that practically destroys the star
A star that will be visible for several month or years that no one has recorded then it will fade away
An extremely dense small dark star in which atomic particles (electrons and protons) have combined to from neutrons
The many types of objects that Messier and Dreyer cataloged which are clouds of gas and or dust
A massive and extremely remote celestial object, emitting exceptionally large amounts of energy and typically having a starlike image in a telescope
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