The Arecibo observatory, the largest single dish radio observatory, opened 50 years ago today in Puerto Rico. It occupies a karst sinkhole and is 305 m (1000 feet) across. The dish is spherical instead of parabolic, which means that it can focus in a broad region instead of only one point. Specifically, the error of a spherical mirror is the same at all locations, but there would be varying amount of astigmatism if the mirror were parabolic.
Some of its observations are:
- Mercury’s period of rotation is 56 days, not 88 days as was thought.
- Provided first solid evidence of neutron stars.
- Discovery of the first extrasolar planets.