| Houstrup observatory | Dinamarca | Varde | — |
| Howell Observatory | Estados Unidos | Misisipi | — |
| Hoyerswerda observatory | Alemania | Hoyerswerda | — |
 Hradec Králové Observatory | República Checa | Hradec Kralové | 287 m |
| Huairou Solar Observing Station | República Popular China | — | — |
| Huancayo Magnetic Observatory | Perú | — | — |
| Hubelmatt Observatory | Suiza | Lucerna | — |
| Hudson observatory | Estados Unidos | Nuevo Hampshire | — |
| Huelva Observatory | España | Huelva | — |
| Huenfelden Observatory | Alemania | Hünfelden | — |
 Hume Cronyn Memorial Observatory | Canadá | London | 251 m |
| Hume Observatory | Estados Unidos | Mark West Springs | — |
| Hunters Hill observatory | Australia | Ngunnawal | — |
| Hurbanovo Magnetic Observatory | Eslovaquia | Hurbanovo | — |
| HUT observatory | Estados Unidos | Edwards | — |
| Hutton-Westfold Observatory | Australia | Victoria | — |
| Hvar Observatory | Croacia | Hvar | — |
| Hyde Memorial Observatory | Estados Unidos | Nebraska | — |
| Hyderabad Magnetic Observatory | India | Haidrābād | 500 m |
| Hypatia Observatory | Italia | Rímini | — |
 Hyper-Kamiokande | Japón | Hida | — |
| Hyperion Observatory | España | Caraquiz | — |
| Hésingue observatory | Francia | Hésingue | — |
 Höfingen observatory | Alemania | Leonberg | — |
| Hāwera Observatory | Nueva Zelanda | South Taranaki District | — |
| IAA-AI Atacama observatory | Chile | San Pedro de Atacama | — |
| Iași Astronomical Observatory | Rumania | Condado de Iași | — |
| Ibis observatory | Estados Unidos | Manhattan | — |
 IceCube | — | Región del Tratado Antártico | — |
| Iga-Ueno observatory | Japón | Tsuge Station | — |
| Iitate Planetary Radio Telescope | Japón | Prefectura de Fukushima | — |
| Ilmala observatory | Finlandia | Helsinki | — |
| Iluro observatory | España | Mataró | — |
 Imaging X-ray Polarimetry Explorer | Estados Unidos | — | — |
| Immanuel Kant observatory | Alemania | Limbach-Oberfrohna | — |
| Inagawa Observatory | Japón | Distrito de Kawabe | — |
| Inastars observatory | Alemania | Potsdam | — |
| Inastars Observatory Potsdam ( before 2006) | Imperio alemán | Potsdam | — |
 Indian Astronomical Observatory (IAO) | India | Hanle | 4.500 m |
| Indian Hill North Observatory | Estados Unidos | Huntsburg | — |
| Ingenio observatory | España | Ingenio | — |
| Ingle Farm observatory | Australia | Ingle Farm | — |
 INPE, Cachoeira Paulista | Brasil | Cachoeira Paulista | — |
| Insperity observatory | Estados Unidos | Humble | — |
 Instalación de Calefacción Ionosférica Sura | Rusia | — | — |
| Institute for Research in Volcanology and Risk Assessment | Portugal | — | — |
 Institute of Avian Research "Vogelwarte Helgoland" | Alemania | Wilhelmshaven | — |
| Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University | Japón | Shimabara | — |