| Kyung Hee Astronomical Observatory | Corea del Sur | — | — |
| Köln observatory | Alemania | Colonia | — |
| L'Ampolla observatory | España | La Ampolla | — |
| L'Aquila Magnetic Observatory | Italia | — | 682 m |
| La Avejerilla observatory | España | Las Palmas | — |
| La Axarquia Observatory | España | Chilches | — |
 La capitale Observatory | Canadá | Quebec | — |
| La Chaux de Fonds observatory | Suiza | La Chaux-de-Fonds | — |
| La Corte Observatory | España | La Antigua | — |
| La Couyere astronomical center | Francia | La Couyère | — |
| La Fecha Observatory | España | Arroyo de la Encomienda | — |
| La Giustiniana observatory | Italia | Roma | — |
| La Mata Observatory | España | La Mata | — |
| La Palma-NEON Observatory | España | Río Gallegos | — |
 La Posta Astro-Geophysical Observatory | Estados Unidos | Condado de San Diego | — |
| La Puebla de Vallbona observatory | España | España | — |
| La Romaneta observatory | España | — | — |
| La Sagra Observatory | España | Don Domingo | — |
| La Senda observatory | España | Cabanillas del Campo | — |
| La Seyne sur Mer observatory | Francia | La Seyne-sur-Mer | — |
| La Vara observatory | España | Muñás | — |
 Laboratoire atmosphères, milieux, observations spatiales | Francia | Guyancourt | — |
 Laboratorio Lincoln | Estados Unidos | — | — |
| Laboratory of Planetology and Geosciences | Francia | Nantes | — |
| LaCaille observatory | Sudáfrica | centurión | — |
 Ladd Observatory | Estados Unidos | Providence | — |
| Lahti Observatory | Finlandia | Lahti | — |
| Laietania observatory | España | Parets del Vallès | — |
| Lake Afton Public Observatory | Estados Unidos | Kansas | — |
| Lake Arrowhead observatory | Estados Unidos | Lake Arrowhead | — |
| Lake Clear observatory | Estados Unidos | Nueva York | — |
| Lake Forest observatory | Estados Unidos | El Dorado Hills | — |
| Lake of the Woods Observatory | Estados Unidos | Lake of the Woods | — |
| Lake Saint Louis observatory | Estados Unidos | Lake St. Louis | — |
| Lakeland Astronomical Observatory | Estados Unidos | Kirtland | — |
| Lamalou-les-Bains observatory | Francia | Lamalou-les-Bains | — |
 Lamont–Doherty Earth Observatory | Estados Unidos | Palisades | — |
| Lamont–Hussey Observatory | Sudáfrica | — | — |
| LAMP observatory | Estados Unidos | New River | — |
| Lancaster observatory | Reino Unido | Lancaster | — |
 Land's End Observatory | Estados Unidos | Colorado | — |
| Landehen observatory | Francia | Landéhen | — |
| Landolt Astronomical Observatory | Estados Unidos | Luisiana | — |
| Langkawi Look Out Point | Malasia | Langkawi District | — |
| Langkawi National Observatory | Malasia | Kedah | — |
| Languard Bird Observatory | Reino Unido | — | — |
| Lanzhou Magnetic Observatory | República Popular China | — | — |
| Large Fiber Array Spectroscopic Telescope | Estados Unidos | Arizona | — |