 Ka-Dar Observatory | Rusia | Karacháyevo-Cherkesia | 2.060 m |
 Ka-Dar Observatory | Rusia | Kuzminskoye | 180 m |
| Kachina observatory | Estados Unidos | Kachina Village | — |
 Kadaň Observatory | República Checa | Kadaň | 399 m |
| Kagiya observatory | Japón | Región de Tokai | — |
| Kahoku observatory | Japón | Kahoku | — |
| Kairos Observatory | Rusia | Rostov | — |
| Kajigamori Observatory | Japón | — | — |
| Kakadu Magnetic Observatory | Australia | Northern Territory | — |
| Kakioka Magnetic Observatory | Japón | Ishioka | — |
| Kalamazoo observatory | Estados Unidos | Municipio de Kalamazoo | — |
 Kalyazin Radio Astronomy Observatory | Rusia | Kaliazin | 86 m |
| Kambah observatory | Australia | Kambah | — |
 Kamenskoe Plateau Observatory | Kazajistán | Alma Ata | 1.450 m |
| Kamihoriguchi observatory | Japón | Ōta | — |
 Kamioka Gravitational wave detector | Japón | — | 414 m |
| Kamioka Liquid Scintillator Antineutrino Detector | Japón | Hida | — |
| Kamioka Observatory | Japón | Hida | — |
| Kanab observatory | Estados Unidos | Cannabis sativa | — |
| Kandilli Magnetic Observatory | Turquía | — | — |
 Kandilli Observatory | Turquía | Estambul | — |
| Kangwon National University Observatory | Corea del Sur | Gangnam-dong | — |
| Kangwon Science High School observatory | Corea del Sur | Wonju | — |
| Kani observatory | Japón | Kani | — |
| Kanoya Magnetic Observatory | Japón | — | — |
 Kanzelhoehe Solar Observatory | Austria | Arriach | — |
| Kappa Crucis observatory | Argentina | Córdoba | — |
| Karasuyama observatory | Japón | Nasukarasuyama | — |
| Karlovy Vary Observatory | República Checa | Karlovy Vary | — |
 Karlsruhe Observatory | Alemania | Karlsruhe | 125 m |
| Karrenkneul observatory | Alemania | Calden | — |
| Karthala Volcano Observatory | Comoras | — | — |
 Kasin Observatory | Irán | — | — |
| Katori observatory | Japón | Distrito de Katori | — |
 KATRIN | Alemania | Karlsruhe | — |
| Katy Observatory | Estados Unidos | Texas | — |
| Kaua‘i Educational Association for Science and Astronomy | Estados Unidos | — | — |
 Kauppi observatory | Finlandia | Tampere | 135 m |
| Kawabe Observatory | Japón | Distrito de Hidaka | — |
| Kawachi observatory | Japón | Kawachi | — |
 Kawaguchi Science Museum | Japón | Kami-Aoki | — |
| Kawane observatory | Japón | Kawane | — |
| Kazo Miraikan | Japón | Kazo | — |
 Keeble Observatory | Estados Unidos | Virginia | — |
| Keetmanshoop Magnetic Observatory | Namibia | — | 1.065 m |
| Kelmis observatory | Bélgica | Kelmis | — |
| Kempshott observatory | Reino Unido | Basingstoke and Deane | — |
| Ken-Ting Observatory | República de China | Condado de Pingtung | — |
 Kennon Observatory | Estados Unidos | Misisipi | — |
| Kenwood Astrophysical Observatory | Estados Unidos | Illinois | — |
 Kepler | — | — | — |
 Kepler-Schule Graz observatory | Austria | Styria | — |
| Kevola Observatory | Finlandia | Paimio | 50 m |
 Kew Observatory | Reino Unido | Richmond upon Thames | — |
| Keyhole Observatory | Italia | Mantua | — |
| Khabarovsk Magnetic Observatory | Rusia | — | — |
 Khajeh Nasir al-Din Tusi Observatory | Irán | Sard-e Sahra Rural District | — |
| Kiel Observatory | Alemania | Kiel | 10 m |
| Kielce observatory | Polonia | Kielce | — |
 Kielder Observatory | Reino Unido | Kielder | — |
| Kiev Magnetic Observatory | Ucrania | — | — |
 Kihoku Astronomical Museum | Japón | Kanoya | — |
| Killer Rocks Observatory | Estados Unidos | Pie Town | — |
 Kilpisjärvi Atmospheric Imaging Receiver Array | Finlandia | Kilpisjärvi | 495 m |
| King City observatory | Canadá | King | — |
| King Edward Point Magnetic Observatory | Islas Georgias del Sur y Sandwich del Sur | — | — |
| Kingsgrove observatory | Australia | Kingsgrove | — |
| Kingsland Observatory | Irlanda | Runnaroddan | — |
| Kingsnake Observatory | Estados Unidos | Seguin | 140 m |
| Kinmen Educational Remote Observatory | República de China | Jincheng | — |
 Kinnordy House | Reino Unido | Angus | — |
| Kinver Observatory | Reino Unido | Stourbridge | — |
 Kirkwood Observatory | Estados Unidos | Indiana | — |
 Kislovodsk Mountain Astronomical Station | Rusia | — | 2.070 m |
 Kiss György Observatory | Hungría | — | — |
| Kitab Observatory | Uzbekistán | Provincia de Kashkadar | 650 m |
| Kitt Peak-Bok observatory | Estados Unidos | Nelson | — |
| Kiyosato observatory | Japón | Kiyosato | — |
| Kiyose and Mizuho observatory | Japón | Kiyose | — |
| Kjell Henriksen Observatory | Noruega | Svalbard | — |
| KM3NeT | — | — | — |
| KMTNet | — | — | — |
| Knielingen Observatory | Alemania | Karlsruhe | — |
| Knocknaboola observatory | Irlanda | Kerry | — |
| KNUE Astronomical Observatory | Corea del Sur | Sejong | — |
| Kochi observatory | Japón | Kōchi | — |
 Kodaikanal Solar Observatory | India | Kodaikanal | — |
| Koeditz observatory | Alemania | Köditz | — |
| Kogota observatory | Japón | Kogota | — |
| Koksijde observatory | Bélgica | Koksijde | — |
| Komakallio observatory | Finlandia | Kirkkonummi | — |
| Konan observatory | Japón | Konan | — |
| Konigsleiten observatory | Austria | Wald im Pinzgau | — |
 Kopernik Space Center | Estados Unidos | Vestal | 530 m |
 Korea Advanced Institute of Science and Technology Satellite 4 | Corea del Sur | — | — |
| Korea Microlensing Telescope Network-CTIO | Chile | Piedras Blancas | — |
| Korea Microlensing Telescope Network-SAAO | Sudáfrica | Karoo Hoogland | — |
| Korea Microlensing Telescope Network-SSO | Australia | Coonabarabran | — |
 Koronas-Foton | — | — | — |
| Koschny Observatory | Países Bajos | Noordwijkerhout | — |
| Kosi Bird Observatory | Nepal | — | — |
| Kottamia Astronomical Observatory | Egipto | El Cairo | 482 m |
| Kouba Observatory | Argelia | Argel | — |
| Kourou Magnetic Observatory | Francia | — | — |
 Kourovskaya observatory | Rusia | Sverdlovsk | 280 m |
 Koyama Astronomical Observatory, Kyoto Sangyo University | Japón | Kita-ku | — |
| Kramatorsk Observatory | Ucrania | Óblast de Donetsk | 76 m |
| Krasnodar observatory | Rusia | — | — |
 Kremsmünster Observatory | Austria | Kremsmünster | 382 m |
 Kryoneri Observatory | Grecia | Sikyona | — |
 Kryzhanivka Observatory | Ucrania | Fontanka rural hromada | 40 m |
| KSA SEM observatory | Corea del Sur | Busan | — |
| KU Observatory | Pakistán | Karachi | 5.000 m |
| Kuban State University Astrophysical Observatory | Rusia | Krai de Krasnodar | 71 m |
 Kuiper Airborne Observatory | Estados Unidos | — | — |
| Kuiper Telescope | Estados Unidos | Pima County | 2.510 m |
 Kulin Observatory | Hungría | Újpest | — |
| Kuma Kogen Astronomical Observatory | Japón | Kumakōgen | 609 m |
| Kumagaya City Cultural Center Planetarium Hall | Japón | Kumagaya | — |
| Kumamoto | Japón | prefectura de Kumamoto | — |
 Kumamoto Civil Astronomical Observatory | Japón | Minami-ku | — |
 Kurashiki Observatory | Japón | Kurashiki | — |
| Kure City Kamagari Astronomical Observatory | Japón | Kure | — |
| Kurihara observatory | Japón | Kurihara | — |
| Kuriwa observatory | Australia | Hawkesbury Heights | — |
| Kurohone observatory | Japón | Kurohone | — |
| Kurume City Observatory | Japón | prefectura de Fukuoka | — |
| Kushiro observatory | Japón | Kushiro | — |
| KUSZA Observatory | Malasia | Terengganu | — |
 Kvant-1 | — | — | — |
 Kwasan | Japón | Yamashina-ku | — |
| KYSUCE observatory | Eslovaquia | Kysucké Nové Mesto | — |
| Kyung Hee Astronomical Observatory | Corea del Sur | — | — |
| Köln observatory | Alemania | Colonia | — |