| Toyama observatory | Toyama | — |
| Toyonaka observatory | Toyonaka | — |
| Toyota observatory | Toyota | — |
| Uenohara Observatory | Uenohara | 747 m |
| Umeenosato Observatory Tenkyukan | prefectura de Oita | — |
| Usuda Star Dome | Prefectura de Nagano | — |
| Uto Observatory | Uto | — |
| Utsunomiya observatory | Utsunomiya | — |
| Utsunomiya-Imaizumi observatory | Utsunomiya | — |
| Uzurano observatory | Kasai Station | — |
| Volcano Research Center | — | — |
| Wakayama observatory | Wakayama | — |
| Yamada observatory | Yamada | — |
| Yamagata observatory | Yamagata | — |
| Yamamoto observatory | Yamamoto | — |
| Yame City Star Culture Museum | Yame | — |
 Yanagida Observatory Mantenboshi | Noto | — |
| Yatsugatake South Base Observatory | Hokuto | — |
| Yatsugatake-Kobuchizawa observatory | Hokuto | — |
| Yatsuka observatory | Yatsuka | — |
| YCPM Kagoshima Station | Kagoshima | — |
| YGCO Chiyoda Station | Chiyoda | 7 m |
| YGCO Hoshikawa and Nagano Stations | Hoshikawa | — |
 Yohkoh | — | — |
| Yorii Observatory | Yorii | 140 m |