I have just purchased the DVD of this Henson fantasy. Once every 1000 trines (for the sake of this post assume they mean years) the three suns of Thra line up in the sky. Yes, it is fantasy, but does the Great Conjunction make any sense at all? Best I can think of would be Thra revolves around a red dwarf, which is about one AU from a solar type star. The pair revolves around a large red giant once every 2000 years. Thra would be about 0.1 AU from the red dwarf, and is either synchronous with it (which would give long, long days) or is rotating independantly (which would give high, high tides). Wich choice is least implausible? With long days, you could have an atmosphere better at evening heat than Earth's, perhaps. Is that possible? If Thra rotates with respect to the red dwarf, could it do so long enough for life to evolve? Even if, as a fantasy, Thra is only a few thousand years old, would the tides by eroding or even flooding the continents? Would any of the bodies of this system be out of the Hill radius?
It would look nothing like the movie...something like an annular eclipse. But thanks for indulging me in trying to visualize one of my favorite movies.