Can humans body clock adjust to different length day for survival on other planets?
The wikipedia article on circadian rhythms says this about rythm plasticity: “The circadian rhythms of humans can be entrained to slightly shorter and longer periods than the Earth’s 24 hours. Researchers at Harvard have recently shown that human subjects can at least be entrained to a 23.5-hour cycle and a 24.65-hour cycle (the latter being the natural solar day-night cycle on the planet Mars).” [from “Plasticity of the Intrinsic Period of the Human Circadian Timing System” by Scheer, Wright, Kronauer, & Czeisler.] Menstrual cycles, to the best of my knowledge, are not affected in space. Retrograde menstruation (reversed flow) and consequent endometriosis was a concern during the early space program, and female astronauts were given hormones to avoid menstruation in space, but women menstruated anyway and it was no different from than what happens on Earth. As for calendars, no one has developed any for other planets, but they will probably be worked out should we begin to colonise ot
