The solar observatory at Uaxactun was used to observe the equinox and solstice stations of the Sun. The long count dates on stelae 18, 19, and 20 are seperated by 7 K'atun, which is equal to 138 tropical years and a remainder of -3.43 days.
Stela 18, 19: 8.16.0.0.0 |
Stela 20: 9.3.0.0.0 |
Other dates as given by Kelley (1983:179-84) supports the expectation, that they represented one of the tropical year stations. A mean long count date as a tropical year station would be 9.15.12.11.11 5 Chuwen 4 Wayeb.