Corrected entry: The astronauts should had immediately realized they were back on Earth, at the beginning of the movie, if they had only gazed at the Moon or constellations in the night time sky (even if it was the year 3978). Naturally that observation would have made that a different movie.
Larry Koehn
15th Sep 2003
Correction: A comment is made very early in the movie about the thunder and lightning with no rain and how there is a strange luminescence but no moon, which would make the stars invisible too. The climate and night sky may have been drastically changed by whatever has happened in the years since they have been traveling.
ChiChi