| 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 | — |