a large system of stars held together by mutual gravitation and isolated from similar systems by vast regions of space
the angular distance of a heavenly body above the horizon
the brightness of a star in comparison with that of the sun: the luminosity of Sirius is expressed as 23 and indicates intrinsic brightness 23 times greater than the sun
the fainter of the two stars that constitute a double or binary star
the magnitude of a star as it would appear to a hypothetical observer at a distance of 10 parsecs or 32.6 light-years