For both Titan occultations described below, the centrality of the occultation will be visible from some places on the Earth. The centrality allows one to observe the "central flash" due to the focusing of the stellar rays by Titan's atmospheric refraction (very much like microlensing events, except that in the case of Titan, the focusing is due to refraction, not gravity).
This flash is a very unique way to measure accuratley (to within a couple of km) the shape of Titan's atmospheric isobar near 0.25 mbar, hence giving a very tight constraint on the zonal wind system of the satellite.
Titan's central flash was observed only once, on 3 July 1989, during the occultation of the bright star 28 Sgr (V=5.5) by the satellite. Details on the method and the results are given in the paper:
Hubbard, Sicardy et al., Astron. Astrophys., 1993.
You can download this article (pdf zipped article, 1.1 Mb) by
clicking here .
Some of the results of the 1989 campaign are show in the figures below, with the retrieval of the isobar shape and the zonal wind profile.
This zonal wind system is an important parameter of Titan's atmosphere dynamics, especially one year before the NASA/ESA space mission Cassini/Huygens gets to Titan and Saturn (December 2004).
The central flash itself will last for typically 10 sec. Therefore, it is wishable to have a typical cycle time of a second or less in order to sample correctly the central flash.