Mimicking the Earth’s Axis
The 140-foot telescope in Green Bank, West Virginia is the largest equatorially-mounted telescope in the world. That means that it moves on a gear parallel to the equator of the Earth because it spins on an axis aligned to that of the Earth. In this photo, its two axes of motion are in view. One is the giant white semi-circular tube with just-visible toothy gears around its edge. This gear is driven by the polar shaft which is aligned to the axis of the Earth (the white shaft braced at the right end of the deck and aiming up at an angle pointing to about 10 o’clock). When the Earth turns, this axis turns in the opposite way, to keep the 43-meter dish aimed on the sky. The tilting gear is the wedge shape under the dish’s support structure.
Credit: NRAO/AUI/NSF
