nadir Nagler eyepiece Naiad naked-eye star naked singularity nakhlite Nançay nanometre nanosecond Narrabri narrow-band photometry NASA Nasmyth focus National Aeronautics and Space Administration National Optical Astronomy Observatories National Radio Astronomy Observatory National Solar Observatory Nautical Almanac nautical twilight n-body problem NEA NEAR Near-Earth Asteroid Rendezvous mission Near-Earth Asteroid Tracking system near-Earth object NEAT nebula nebular hypothesis nebulium NEO Neptune Nereid Net neutral hydrogen neutrino astronomy neutron star New General Catalogue of Nebulae and Star Clusters new generation telescope new Moon New Style Date New Technology Telescope Newtonian telescope Next Generation Space Telescope N galaxy NGC NGST nightglow Nix Olympica NLC NNTT NOAO noctilucent clouds Noctis Labyrinthus nocturnal node noise non-thermal radiation Nordic Optical Telescope Norma normal galaxy normal reflectivity North America Nebula Northern Cross Northern Crown northern lights North Galactic Spur north polar distance North Polar Sequence North Star nova NPD NRAO NSO N star NTT Nubecula Major Nubecula Minor nucleosynthesis Nuffield Radio Astronomy Laboratories Nunki nutation Nysa