A albedo Alpha Centauri apogee asteroid astronaut astronomer astronomy B background radiation binary star black hole C cluster comet conjunction constellation corona cosmonaut crater D dark matter day dwarf planet | E Earth eclipse ecliptic escape velocity F flare G galaxy geosynchronous gibbous H hydrogen helium Hubble I ionosphere J Jupiter K Kepler Kuiper | L light-year local group lunar M magnitude Mars mass Mercury meteor meteor shower meteorite meteoroid Milky Way moon N nadir NASA nebula Neptune neutron star nova | O observatory Oort opposition orbit P parallax parsec penumbra perigee perihelion perturbation phase planet planetary nebula planetoid Pluto pulsar Q quasar R radiant radiation revolve rocket | S satellite shooting star solar solar system solar wind solstice space space station star sun sunspot supernova T telemetry telescope U umbra Uranus V vacuum Van Allen belt Venus Z zenith |