Computers also played a part in the MMT’s mounting. The MMT used an altitude-azimuth mounting, which could move both up and down as well as left and right, around all the points of the compass — like a turret-style gun on a navy ship. Computers constantly adjust the mounting so the telescope can stay on target even though the Earth is rotating. Because the mounting is small and lightweight, the telescope would need less space than earlier telescopes. The dome for the 200-inch Hale Telescope at Mount Palomar in California, for instance, is much larger.
The mounting wasn’t the only moving part. The entire building was designed to rotate to follow the movement of the telescope. Astronomers never knew quite where they would be when they stepped out the door.
Airing out the issues
The MMT’s mirrors, like all glass mirrors, would expand as the temperature rose and contract as it fell, causing the focal point of the telescope to change. The building around the telescope was designed to open fully to the night air, to allow the telescope to cool quickly to that temperature. Once the telescope reached the temperature of the night air, the focus steadied and the telescope could be used.
