| Abbreviation | Definition |
|---|---|
| TLP | Transient Lunar Phenomenon |
| TMA | Tycho Magnetic Anomaly |
| TMC | Telescope Makers Convention |
| TMN | Tokyo Meteor Network |
| TMT | Thirty Meter Telescope |
| TNE | Time of Next Event |
| TNM | The New Millenium |
| TRACE | Transition Regional And Coronal Explorer |
| TRAO | Taeduk Radio Astronomy Observatory |
| TRAPPIST | Transiting Planets and Planetesimals Small Telescope |
| TSI | Total Solar Irradiance |
| TSRS | Trieste Solar Radio System |
| TSS | Texas supernova survey |
| TT | Terrestrial Time (replaced Ephemeris Time, ET) |
| TT | Transit Traverse |
| UACN | UAE Astronomical Cameras Network |
| UAO | Unidentified Aerial Object |
| UAO | Uppsala Astronomical Observatory |
| UAT | Unified Astronomy Thesaurus |
| UBV | Ultraviolet Blue Visual photometry |