Fabry-Perot interferometer facula(1) facula(2) fall falling star false colour image False Cross Faraday rotation Far-Infrared and Sub-millimetric Space Telescope farside Far Ultraviolet Spectroscopic Explorer F corona feedhorn Fermi-Hart paradox fibre optics fibril field equations field galaxy field of view field pattern field star figuring filament filar micrometer filter filtergram find finder fireball(1) fireball(2) FIRST first contact First Point of Aries first quarter Fishes FK Flaming Star Nebula Flamsteed numbers flare flare star flash spectrum flat flatness problem flexus flocculi Flora Flora group fluctus flux collector flux density Fly flyby Flying Fish Foal focal length focal plane focal ratio following Fomalhaut Footprint Nebula forbidden lines fork mounting Fornax Fornax A Forty-seven Tucanae fossa Foucault knife-edge test Foucault's pendulum fourth contact Fox Fra Mauro Franklin Adams charts f-ratio Fraunhofer lines Fred Lawrence Whipple Observatory frequency Friedmann universe F star F-type asteroid full Moon fundamental catalogue fundamental epoch fundamental plane FU Orionis star Furnace FUSE f-value