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Finder 8x50 black. Straight view. Complete

 Price:   £75.00

Finder 8x50 black. Right Angled view. Complete

Price:   £85.00

Finder complete 6x30 black

Price:   £35.00

Celestial Sphere

The projection of space onto the night sky, an imaginary hollow sphere of infinite radius surrounding the Earth but centred on the observer. (First postulated by Ptolemy.) It is the basis of sky charts, and the celestial co-ordinate system. The coordinate system most commonly used is right ascension and declination.

Astronomical Unit. (AU)

This is the mean distance from the Earth to the Sun, i.e. 149,597,870 km. (approx 93 million miles)

Red Giant

A spectral type K or M star nearing the end of its life having a low surface temperature and large diameter eg Betelgeuse in Orion.

Aperture

The size of the primary optical surface of an astronomical instrument (telescope), usually given in inches, centimeters, or meters. In the case of a reflecting telescope, the aperture usually refers to the size of the main mirror; in the case of a refracting telescope (of which binoculars are one example), the aperture refers to the size of the primary lens (which in binoculars is usually given in millimeters).

CCD

Charge-coupled device, a very sensitive electronic device that is becoming popular as a replacement for film-based photography. CCD cameras are composed of silicon chips that are sensitive to light, changing detected photons of light into electronic signals that can then be used to make images of astronomical objects or to analyze how much light is being received from such objects. CCDs require computers for reduction of data, but can detect much fainter objects than can photographs. Unfiltered CCDs tend to be more red-sensitive than the human eye.

Perihelion

The point where (and when) an object orbiting the sun is closest to the sun.

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