The 350 tonne giant needs to move with absolute accuracy, sliding with microscopic precision, almost completely free of friction, to point at and track objects billions of light years away. So what kind of movements does a telescope need to make?
To locate an object in the sky, a telescope moves on two axes. The azimuth (horizontal) and elevation (vertical) movements are used to locate the objects that the telescope will observe.
This works like the cannons aboard a warship: first, the cannon rotates on its base, then it seeks the target in the vertical.
Once the object has been located it must be tracked. Due to the earth’s rotation, the telescope needs to move in three directions, so that the objects being observed remain in focus.
If the telescope’s axis of rotation was parallel to the earth’s, only one type of movement would be needed to track an object. However, as this is not the case, the telescope needs to rotate on three axes: azimuth, elevation and field rotation.
On the GTC, this third movement will be achieved by mounting the instruments on mechanical rotators.
Natalia R. Zelman