Telescope mountings

1. Telescopes have to be able to follow the stars across the sky as the earth rotates.

2. The simplest way to achieve this is the equatorial mount. One axis of the mount is parallel to the earth's axis and the other one is perpendicular to the first. Normal tracking then requires only rotation about a single axis (which one?).

3. Another common way of mounting a telescope is called' altitude-azimuth'. One axis is horizontal and the other is vertical; then tracking a star requires two simultaneous rotations.