INSTRUMENTS

ASTRAL TELESCOPE

page 5

USE OF EQUATORIAL MOUNTING

THE BALANCING AND THE POLAR ALIGNMENT OF THE EQUATORIAL MOUNTING
for models with equatorial mounting. Some models of telescope, usually known as "equatorial" are equipped with a special accessory or "support" - EQUATORIAL MOUNTING (fig. 5).

This permits the movement of the telescope in all directions, and, in particular, allows the "following" or tracking of celestial objects while turning on one axis only - RIGHT ASCENSION (it is often possible to use a small motor to set the operation in motion automatically). Certain preliminaries must be carried out before using this support: i.e. the balancing and the equatorial positioning.

To balance the instrument it is necessary first to incline the polar axis to a degree approximating your latitude, unscrewing the appropriate screw on the side of the mounting and aligning the indicator needle to the relative value on the scale of latitude.
After regulation, tighten the screw well. Immediately afterwards rotate the telescope on the polar axis in such a way that the axis of declination, and the counterbalancing axis are parallel to the land (fig 6a).

The tube of the telescope, with the screw of the polar axis unblocked, will tend to fall downwards, or else, on the other hand, will fall towards the counterbalance. Move the counterbalance along the axis until the system is perfectly balanced.
Leaving it in that position, turn the screw of the Right Ascension axis and unscrew that of the Declination Axis. The tube of the telescope will be inclined (fig 6b) towards the front or back and it will be necessary to move the tube inwards so that the mounting is balanced in this direction also.
N.B. In certain models the tube of the telescope will be fixed to the mounting with two screws. In this case it will not be necessary to effect this second procedure.

This equatorial telescope can be regulated:  as follow the apparent motion of celestial body.
This motion will be in the opposite direction to that of earth on its axis. (fig 7). Simply point the polar axis of the telescope towards the Celestial North Pole, bringing this mechanical axis parallel to the terrestrial one and thereby allowing you to point at the stars, basing this on the data available on the maps and star catalogues

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In short, you will be putting your telescope at the center of the celestial sphere as though at the center of a wheel. The angle of declination has a value of 90 ° minus the angular distance of the Celestial Pole. The Celestial Pole can be found at 90 °. If you find yourselves at the North Pole, you will have to point the polar axis of the telescope vertically, that is towards the Celestial North. To compensate the effect of your position on earth, the polar axis will be inclined to a degree corresponding to your geographical latitude, as we have already said. The procedure in detail is as follow:

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  1) Mount the telescope at night. Unblock the screws on the declination axis and rotate the telescope until you read the value of 90 ° on the gauge. Screw in the blocking screws. The optic tube of the telescope is now parallel to the polar axis.
   

• 2) Loosen the screws of the horizontal movement of the mounting and rotate the telescope until the tube is pointing north. You can identify the North by recognizing the position of the Polar Star or by means of a compass to identify the magnetic north. True North will coincide with the position of the Polar Star while magnetic north differs slightly from the True North.
   

• 3) Find the latitude of your position on a geographical map. If you have not already done so (see page 78) unscrew the screw locking the inclination of the polar axis and incline this axis so that you can read on the scale of latitude its relative value. Point the finder towards the Polar Star. This will probably not be round at the center of the reticule. One of the possible motives will be due to the incorrect orientation of the polar axis in respect to the horizontal one.
  Unblock the screw once again on the horizontal movement and rotate the telescope around on this axis until it is pointed towards the Polar Star. Tighten both levers well. The Polar Star is about 1 ° away from the Celestial North Pole.
  Because of this, in the course of successive observations you will need to make corrections to your positioning in order to compensate for small errors of alignment.