aberration accretion disc AGN Alpha Centauri apoapsis asteroid asteroid belt binary star black hole brown dwarf Callisto celestial latitude celestial longitude cluster conjunction Crab Nebula declination double star Earth eclipse epoch equinox Europa galactic plane galaxy heliosphere hour angle Hubble's constant Hubble's Law inclination inferior conjunction Io Jupiter Kepler's law nebula nebular nebulus Neptune neutron star Oort cloud orbit orbital plane Orion periapsis phase planet Pleiades Pluto point of apoapsis point of periapsis precession protostar quasar radio telescope red dwarf red giant Red Planet red shift retrograde right ascension rotation curve satellite Saturn SETI spiral galaxy star sun supercluster supergiant superior superior conjunction supernova telescope universe Uranus variable star Venus vernal equinox white dwarf