The fixed stars (from the Latin stellae fixae) are celestial objects that do not seem to move in relation to the other stars of the night sky. Hence, a fixed star is any star other than the Sun. A nebula or other starlike object may also be called a fixed star. People in many cultures have imagined that the stars form pictures in the sky called constellations. In Ancient Greek astronomy, the stars were believed to exist on a giant celestial sphere, or firmament, that revolves daily around Earth.