On March 7, 1962, NASA launched the first Orbiting Solar Observatory. [‘On This Day in Space’ Video Series on Space.com](https://www.space.com/39251-on-this-day-in-space.html)

Eight of these satellites were launched between 1962 and 1975 to study the 11-year solar cycle. Each of the satellites had two main parts called the "wheel" and the "sail." The sail contained solar panels and instruments that took measurements of the sun. The sail was mounted onto the wheel, which could rotate to make sure that the instruments were pointing in the right direction. The satellites measured things like UV light, X-rays, and gamma radiation. The data was recorded on tape and transmitted to Earth via FM telemetry.