quark: a (charged) elementary particle that feels the strong force. Protons and neutrons are each composed of three quarks.
quasar: A starlike object thought to consist of an enormous rotating black hole with large amounts of matter falling into it. The matter gets very hot and emits a lot of energy before it falls inside the black hole. Quasars are extremely distant, but can be observed because they are so powerful.
radar: A system using pulsed radio waves to detect the position of objects by measuring the time a single pulse takes to reach the object and be reflected back.
radio telescope: A telescope that makes maps of the positions in the sky of sources
