(2240) Tsai Main-belt Asteroid
Discovered on 30 December 1978 by Harvard Observatory at Harvard.
Named in honor of Tsai Chang-hsien, director of the Taipei Observatory since World War II, an active observer of planets and variable stars, and a long-time popularizer of astronomy. He has enlightened the public and directed amateur activity in astronomy for more than three decades with great patience and dedication.Naming citation (MPC 5360), IAU / Minor Planet Center, via NASA/JPL
Where Tsai is today
Seen from above the solar system on 2026-10-14: Tsai is 3.60 au from the Sun and 3.95 au from Earth. Computed from JPL's orbital elements.
Facts
| Number | 2240 |
| Provisional designation | 1978 YA |
| Orbit class | Main-belt Asteroid |
| Diameter | 24.4 km (#1,737 largest of 17,440 named asteroids with a measured size) |
| Albedo | 0.0570 |
| Rotation period | 4.42 hours |
| Absolute magnitude (H) | 11.99 |
| Orbital period | 5.61 years |
| Semi-major axis | 3.16 au |
| Perihelion – aphelion | 2.70 – 3.62 au |
| Eccentricity | 0.145 |
| Inclination | 0.839° |
| Closest distance between its orbit and Earth's (MOID) | 1.72 au |
Data: NASA/JPL Small-Body Database and the IAU Minor Planet Center.