quantized The fact that light and matter on small scales behave in a discontinuous manner, and manifest themselves in the form of tiny "packets" of energy, called quanta.

quarter Moon Lunar phase in which the moon appears as a half disk.

quasar Star-like radio source with an observed redshift that indicates extremely large distance from Earth.

quasi-stellar object (QSO) See quasar.

quiet Sun The underlying predictable elements of the Sun's behavior, such as its average photospheric temperature, which do not change in time.