labes labyrinthus Lacerta Lacertid lacus Lagoon Nebula Lagrangian points Langrenus La Palma Large Binocular Telescope Large Magellanic Cloud Larissa Las Campanas Observatory Laser Interferometer Gravitational-Wave Observatory laser ranging La Silla Observatory last quarter late-type star latitude LBT LDEF leap second leap year Leda Lemaître universe lens lenticular galaxy Leo Leo Minor Leonids lepton era Lepus Lesser Dog Lesser Water Snake Lexell's Comet LHA Libra libration Lick Observatory light bucket light curve light echo light pollution light-time light year LIGO limb limb brightening limb darkening limiting magnitude linea line profile liner line spectrum Linné Lion Lion Cub lithosiderite lithosphere Little Bear Little Dipper Little Dog Little Dumbbell little green men Little Horse Little Lion Lizard LM LMC LMST Local Bubble Local Cloud Local Group local hour angle local mean solar time local sidereal time local standard of rest Local Supercluster local time Loki long-baseline interferometry Long Duration Exposure Facility longitude longitude of perihelion longitude of the ascending node long-period comet long-period variable look-back time Lost City Meteorite Lovell Telescope Lowell Observatory LRV LSR LST luminosity luminosity class luminosity function Luna lunar lunar eclipse Lunar Orbiter lunar parallax Lunar Prospector Lunar Roving Vehicle lunation Lund Observatory Lunik lunisolar precession Lunokhod Lupus l.y. Lyman-alpha forest Lyman series Lyndon B. Johnson Space Center Lynx Lyot filter Lyra Lyre Lyrids Lysithea