INSTRUMENTS

ASTRAL TELESCOPE

BASIC NOTES

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MOUNTING FOR THE TELESCOPE
By "mounting" is meant the mechanical parts which allows the instrument to be pointed at the object to be observed. Many small telescopes are equipped with tripod attachments enabling them to be used with this type of accessory. In order to allow accurate astronomy observation the telescope has to be movable on two axes. The direction of these axes deter mines the type of mounting required.

ALTAZIMUTH MOUNTING

The axes for azimuthal mounting (fig. 10) are set, one zenith wards (the vertical axis) and the other, perpendicular to the first, horizontally (horizontal axis). Whit this type of mounting, simple to set up, contemporaneous movement of the two axes is needed to follow celestial objects. This type of mounting is used almost exclusively by small telescopes where photography is not required.

PARALLACTIC OR EQUATORIAL AXIS

In this type of mounting, the axes are positioned with one parallel to the terrestrial rotation axis (polar axis) and the other perpendicular to that (declination axes). This system, besides being very steady and precise, allows the observation of terrestrial objects by means of one movement only (once the equatorial positioning has been made) rather than by two, as in the case of the azimuthal mounting. This permits the use of a small mechanism that automatically follows the object. This is a very practical system for observation, indispensable for those who want to take long exposure photographs. The most widely used mounting is the "German" type (see fig. 11) particularly suitable for long instruments such as reflector and refractor telescopes. Also popular is the Forcell which is used for some types of Catadioptric telescope.