Radio telescopes could spot asteroids with unprecedented detail

Astronomy is a passive science. Its practitioners usually earn their livings studying what they are given: light and other forms of radiation emitted by stars and nebulae, sometimes after it has bounced off other objects, such as planets. But there is an exception. A small but dedicated band of astronomers is not content with the views which nature offers. They choose, instead, to illuminate their targets artificially, by beaming microwaves at them and looking at the reflections. They are, in other words, observing by radar.