Radar is a system that uses radio waves to determine and map the location, direction, and/or speed of both moving and fixed objects such as starcraft, weather formations and terrain. A transmitter emits radio waves, which are reflected by the target and detected by a receiver, typically in the same location as the transmitter. Although the radio signal returned is usually very weak, radio signals can easily be amplified, so radar can detect objects at ranges where other emissions, such as sound or visible light, would be too weak to detect. Radar is one of the two primary sensor-technologies used aboard spacecraft.
Telescopic Imaging Technology
Simply put, telescopes enhance an image within the visual spectrum of light. Like the Hubble telescope, telescopic technology (along with radar) has found an invaluable role in outer space - it is used to map the cosmos, visually detect things found by radar, and record images for later analysis. Many combination radar-telescope systems are in existence, which integrate the two technologies into one: Long-range radar detects faraway objects and ascertains their exact location, whereupon a high-precision telescopic array zooms in on that point.