With electric lights and all our glowing gadgets and gizmos interfering with our natural day-night/sleep-wake rhythms, it is surprising how much our bodies still respond to basic geological cues. A new study found that the lunar cycle influences our sleep—even when we can’t see the moon and have no idea what phase it’s in. Around a full moon, participants took longer to fall asleep, had 30 percent less deep sleep and slept 20 minutes less overall.

MORE: Are Night Owls Evil? Science Considers.