Killing Sunday-Keeping Aliens?

In our last StandingWatch program, titled, “Killing Sabbath-Keeping Aliens,” we spoke about the science fiction movie, The Tomorrow War, pointing out that these hostile aliens were keeping and resting on the seventh day—the Sabbath—and had to be destroyed. The question arose whether the reference to the seventh day—the Sabbath—was not actually a reference to Sunday. Is Sunday the biblical Sabbath? What is the Truth?