Data taking: November 1989 to March 1993.
Mean epoch: 1991.
| Number of sources | 118,000 |
|---|---|
| Faintest Star | 12.5 mag |
| Positional accuracy (1 sigma) | 0.001" |
| Photometric accuracy (1 sigma) | 0.002 mag |
Tycho Catalog
| Number of sources | 1,000,000 |
|---|---|
| Magnitude Limit | 11.5 |
| Positional accuracy (1 sigma) | 0.025" |
| Photometric accuracy (1 sigma) | 0.06 mag |
| Proper Motion accuracy (1 sigma) | tbs |
| Accuracies for mag < 9.5 | |
| Positional accuracy (1 sigma) | 0.01" |
| Photometric accuracy (1 sigma) | 0.02 mag |
As a result of the large proper motion errors, the accuracy of the Tycho positions degrades linearly with time. If the average proper motion is 0.02"/year (number needs to be calculated more accurately), then this results in a sigma in the position of 0.02" times the number of years between the 2MASS observation and the Tycho mean epoch. This results in the following positional accuracies for either the Tycho or Hipparcos catalog stars:
| Year | Positional accuracy (") (1 sigma) |
|---|---|
| 1997 | 0.12 |
| 1998 | 0.14 |
| 1999 | 0.16 |
| 2000 | 0.18 |