@DenOfEarth @liamvhogan @anna @astronomerritt @nyrath @isaackuo Variants on this approach were fairly standard in large telescopes up until the mid 1970's when computer control systems able to do the required trigonometry digitally took over. Coincidentally one of the first examples of the latter was the Anglo-Australian Telescope, at the same observatory (Siding Spring) as the UK Schmidt Telescope and its phantom.

Numerous radio telescopes and at least some of the Deep Space Network communication dishes used what they called a Master Equatorial, effectively a model of an equatorial mount telescope being used to mechanically compute the required position for the real altitude-azimuth mounted telescope.

This is the Murriyang/Parkes Master Equatorial, which as far as I know is still in use: https://www.atnf.csiro.au/daily-picture/2017/09/11/the-parkes-master-equatorial/

@liamvhogan For anyone that's wondering, the phantom that room contained was this thing, the UK Schmidt Telescope's phantom. It is a specialised electro-mechanical computer, used by the telescope's original control system to keep the telescope dome and its windscreen aligned with the telescope itself. It has since been exorcised from the phantom room and banished to an unused office.

The pointer in the middle of the phantom was linked to the telescope drives, and pointed in the direction the telescope was looking. As it moved it pushed the white arch (representing the dome) and the D-shaped frame (representing the dome windscreen) around. Sensors on the arch & frame were linked to the dome & windscreen drives, making them follow the telescope. The phantom enabled the UK Schmidt Telescope to do real time coordinate tranformations without needing an electronic computer at all from 1973 to 2013.

Photos by me, from 2019.

@liamvhogan Spooky.