Space travel can be exciting — and restless! NASA researchers are exploring ways to help astronauts enjoy a better night’s sleep on the space station … and beyond. Take the exploration of Mars, for example. On Mars, daylight is primarily yellowish-brown. On Earth, it’s blue-green. How will the human clock respond to the unearthly color of Martian skies? Some research indicates that it could make a difference. Melatonin production, for example, is suppressed more by some wavelengths of light than by others. Of more concern, perhaps, is the length of the Martian day: 24 hours and thirty-nine minutes. “That is significantly different than the period of the clock in humans,