| The longest days of the year just slipped by, and the sun’s still not setting until about 9:30 p.m. in both Berlin and London. In Newcastle in northern England, roughly at the latitude of the Alaska Peninsula, it never gets totally dark. Staying up all night is a summer solstice tradition across northern Europe. But having sunrise and sunset out of sync with our typical daily schedules can also be confusing for the body’s internal clock. “Instead of everything being beautifully aligned, everything starts to drift apart,” says Russell Foster, a professor of circadian neuroscience at the University of Oxford. The body’s natural cycle of sleep and waking is a bit longer than 24 hours, so in our day-to-day lives, we’re constantly adjusting our internal rhythm to match the clock. Studies have shown that in times of midnight sun, it’s possible to follow either, says Malcolm von Schantz, a professor of chronobiology at Northumbria University. In one study, the British Antarctic Survey chose to hew to UK time, Von Schantz said. “They do wake up, and they do fall asleep, and bodies seem to cope with that,” he says. In contrast, in a study on Greenpeace volunteers in the Antarctic, people didn’t stick to an external schedule and returned to the longer daily biological clock, he says. But when it comes to the body’s own clock, it’s not bright light in the evening that’s the biggest factor, says Michael Gradisar, head of sleep science at the app SleepCycle AB. It’s light in the morning. People have a tendency to sleep in later during the dark months of the year, he says. In Germany, for example, SleepCycle users slept 22 minutes longer in December than in June last year. That translates into going to bed later as well, he says, because it takes longer to “build up your sleep pressure” to be ready to fall asleep in the evening. So for people trying to get back onto an earlier schedule after too many midsummer parties, Gradisar recommends letting in a bit of morning light. A University of Colorado study found that a weekend of camping was able to shift night owls toward an earlier circadian rhythm, he notes. “If you remove people from their artificial sources of light and dark and you attune them to nature, then their rhythm goes toward the timing of nature,” he says. The Colorado study was based on a light-dark cycle of about 14 1/2 hours of light and 9 1/2 hours of darkness. Here in Berlin and London, we won’t return to that until the end of the summer — late August and early September, respectively. Until then, we’ll be cracking open our blackout blinds and stepping out for some early-morning sun. — Naomi Kresge and Elliot Burrin | 
