 Wyoming Infrared Observatory | Estados Unidos | Condado de Albany | — |
| Wyrick Observatory | Estados Unidos | Haymarket | — |
| Würzburg University Observatory | Alemania | Wurzburgo | 186 m |
| XEUS | — | — | — |
 Ximenian Observatory | Italia | Florencia | — |
| Xingming observatory | República Popular China | Urumqi | — |
| Xingming Observatory | República Popular China | Urumqi | — |
| Xingming Observatory #2, Nanshan | República Popular China | Urumqi | — |
| Xingming Observatory #3, Nanshan | República Popular China | Urumqi | — |
| Xingming Observatory-KATS | República Popular China | Urumqi | — |
 XMM-Newton | — | — | — |
 XRISM | — | — | — |
 Xujiahui Observatory | República Popular China | Shanghái | — |
 Xuntian | República Popular China | — | — |
| Xuyi Astronomical Observatory of Purple Mountain Observatory | República Popular China | — | — |
| Yakutsk Magnetic Observatory | Rusia | — | — |
| Yale Observatory | Estados Unidos | Bethany | — |
| Yale Student Observatory | Estados Unidos | New Haven | — |
 Yale University Observatory | Estados Unidos | Connecticut | — |
 Yale-Columbia Station | Sudáfrica | Johannesburgo | 1.762 m |
| Yamada observatory | Japón | Yamada | — |
| Yamagata observatory | Japón | Yamagata | — |
| Yamamoto observatory | Japón | Yamamoto | — |
| Yame City Star Culture Museum | Japón | Yame | — |
 Yanagida Observatory Mantenboshi | Japón | Noto | — |
| Yatsugatake South Base Observatory | Japón | Hokuto | — |
| Yatsugatake-Kobuchizawa observatory | Japón | Hokuto | — |
| Yatsuka observatory | Japón | Yatsuka | — |
| YCPM Kagoshima Station | Japón | Kagoshima | — |
| Yellow Springs observatory | Estados Unidos | Yellow Springs | — |
| Yellowknife Magnetic Observatory | Canadá | Territorios del Noroeste | — |
 Yerevan Observatory | Armenia | Kentron | — |
| Yerres-Canotiers observatory | Francia | Yerres | — |
| YGCO Chiyoda Station | Japón | Chiyoda | 7 m |
| YGCO Hoshikawa and Nagano Stations | Japón | Hoshikawa | — |
 Yohai Lookout | Israel | Ashdod | — |
 Yohkoh | Japón | — | — |
| Yonsei Survey Telescopes for Astronomical Research | Sudáfrica | Sutherland | — |
| Yorii Observatory | Japón | Yorii | 140 m |
 York University Observatory | Canadá | Ontario | — |
| Younchun observatory | Corea del Sur | Yeoncheon | — |
| YSVP observatory | Australia | Vale Park | — |
 Yuba City Astronomical Observatory | Estados Unidos | California | — |
| Yunling Observatory | República Popular China | Yao'an | — |
 Yunnan Astronomical Observatory | República Popular China | Kunming | 2.014 m |
| Yunnan-HK Observatory | República Popular China | Yulong | — |
| Yunquera observatory | España | Yunquera | — |
| Yuri Gagarin National Astronomical Observatory and Planetarium | Bulgaria | Stara Zagora | — |