Solar radar

On this day in 1959, scientists obtained the first radar echoes from the Sun. Science magazine called the feat “man’s first direct contact with the Sun.” Scientists at Stanford University used a Collins FRT-22, a radar transmitter often used by the military, to beam 40 kilowatts of 25.6 megahertz radio waves. It takes radio (and any wavelength of light) more than 16 minutes to get to the Sun and back, so after 15 minutes of transmission the scientists fitted an antenna to the equipment, turning it into a radio receiver. After saving the data on magnetic tape, an IBM 797 computer analyzed the measurements over the next several months. The results were baffling to astronomers at the time, who knew little or nothing about phenomena such as coronal mass ejections and the solar wind. In the subsequent decades scientists have learned much more about our resident star, though they’d still love to be able to predict solar storms and other outbursts that can disable satellites and the electrical grid. (Figure from V.R. Eshleman, R.C. Barthle, P.B. Gallagher, Science 1960. Hat tip to Corey Powell on Twitter.)

Date in History: 7 April 1959