Radar stands for “[RA]dio [D]etection [A]nd [R]anging.” It’s a sensor that generates microwave radiation (let’s call it a “signal”) and uses that signal to detect and locate objects. A radar can do this because the signal it sends out (or “transmits”) bounces off material in its path in different ways. How the signal bounces off the material depends on the composition of the material, from what direction the signal is traveling, the frequency of the radar’s transmitted signal, and the size and shape of the object.

What kinds of things are radar used to observe? The first applications of radar devices were the upper atmosphere and lightning, and, of course, military-related (i.e.: to locate air, ground, and sea targets). These days, a typical object for a radar might still be an aircraft or a ship, but also natural objects, like precipitation (as with your weatherman’s Doppler radar), ice, aurora, spacecraft, and celestial objects. Your radar might be on the ground, attached to the bottom of an aircraft, or part of a payload on a satellite in space.

Regardless of whether your radar is on the ground or in space, when a radar signal reaches its intended object, a couple of things happen. As with the optical light you see with your eyes, a radar signal will either reflect off the object back to the radar, scatter in many different directions, or bend around the object in a process called “diffraction”. Depending on the objects being observed, the wavelength of the signal, and how the signal gets back to the radar, the radar will discern different properties of the object, including location, size, roughness, and speed.