L
| Name | Established | Location |
| Laboratoire d'Astrophysique de Grenoble | 2001 | Grenoble, France |
| Observatorio de La Cañada (La Cañada Observatory) | 2002 | Ávila, Spain |
| Ladd Observatory | 1891 | Providence, Rhode Island, USA |
| Lake Afton Public Observatory | 1979 | Wichita, Kansas, USA |
| Lamont–Hussey Observatory (defunct) | 1928 | Bloemfontein, South Africa |
| Landessternwarte Heidelberg-Königstuhl | 1898 | Königstuhl, Heidelberg, Germany |
| La Plata Astronomical Observatory | 1883 | La Plata, Argentina |
| La Silla Observatory | 1969 | Atacama Desert, Chile |
| Large Millimeter Telescope | Sierra Negra, Puebla, Mexico | |
| Las Brisas Observatory | 1979 | Colorado, USA |
| Las Campanas Observatory | La Serena, Chile | |
| Laws Observatory | 1880 | Columbia, Missouri, USA |
| Leander McCormick Observatory | 1885 | Mount Jefferson, Charlottesville, Virginia, USA |
| Lee Observatory | 1873 | American University of Beirut, Beirut, Lebanon |
| Leiden Observatory | 1633 | Leiden University, Leiden, Netherlands |
| Leipzig Observatory | Leipzig, Germany | |
| Leoncito Astronomical Complex | 1986 | Calingasta, San Juan, Argentina |
| Levenhagen Observatory | Seattle, Washington, USA | |
| Lick Observatory | 1881 | Mount Hamilton, San Jose, California, USA |
| LightBuckets (commercial observatory) | 2007 | Rodeo, New Mexico, USA |
| LIGO | 1999 | Hanford Site & Livingston Louisiana |
| Llano de Chajnantor Observatory | 2005 | Atacama Desert, Chile |
| Llano del Hato National Astronomical Observatory | 1975 | Mèrida, Venezuela |
| Long Wavelength Array (LWA) | 2010 | Socorro, New Mexico, USA |
| Longa Vista Observatory | 2010 | Itatiba,SP, Brazil |
Lowell Observatory
|
1894
|
Flagstaff, Arizona, USA |
| Lulin Observatory | 1999 | Mount Lulin, Taiwan |
| Lund Observatory | 1749 | Lund, Sweden |
| Luoxue Mountain Cosmic Rays Research Center | 1953 | Luoxue Mountain, Yunnan Province, China |
| Lyon Observatory | 1877 | Saint-Genis-Laval, France |
Read more about this topic: List Of Astronomical Observatories