Q) How should I choose my bottled water?
Adam Sussman, New York, NY
A)DAUNTING, ISN'T IT? All those varieties, all those claims to being the puresthow is a thirsty athlete to decide? Saving any talk of "enhanced" fitness waters for another day, let's look at the health benefits of the two basic kinds: water with stuff, and water without. First there's mineral water, which contains 250 parts per million of dissolved solids like calcium, magnesium, and zinc that's been acquired from underground deposits. (Spring waters, depending on where the spring flows, may have enough mineral content to go in this category, or may be much, much purer.) Eileen Vincent, a nutritionist at Northwestern University, in Evanston, Illinois, confirms that these minerals are a boon to your system but says that since any brand has only a fraction of the stuff you need, it'll never be a substitute for your leafy greens and whole grains. Then there's what we'll call pure water, which has few or no minerals. Mother Nature's purest comes from glaciers and from springs in Norway and Fiji, but most pure bottled water gets that way through filtering processes like reverse osmosis. Whether it comes from Fiji or a filter, says Vincent, it's neither better nor worse than mineral water from a nutrition standpoint. In other words, they're all good for you, so you're free to base your decision on flavor.
Q)When I camp out in the desert, why are fewer stars visible at 4 a.m. than at midnight?
Bradley Smith, Los Angeles, CA
A)EVEN THOUGH the sky might look pitch-black at both times, more stars are obscured in the early morning because that nether time we call twilight actually begins as early as two hours before sunrise (and endures up to two hours past sunset). According to astronomer Jeff Chester, of the U.S. Naval Observatory, in Washington, D.C., there are three distinct phases of twilight. In the morning, the first phase is astronomical twilight; if you were in Palm Springs on the summer solstice, it would arrive at 3:52 a.m., and you would start to see fewer stars than you had an hour earlier. After that, at 4:31, would come nautical twilight (when the user of a sextant can see both the horizon and the major stars) and, at 5:07, civil twilight (when it's light enough for people to do "normal outdoor activities" without artificial light). Civil twilight is the indigo phase that most of us know as twilight, and only a few stars would still be visible, fading out until the sun first appeared, at 5:36 a.m.
Q)What are snow cups?
Tammy Lundquist, South Lake Tahoe, CA
A)BETTER KNOWN as sun cups or, technically, ablation hollows, these dimplelike depressions form on snowfields that have been exposed to prolonged intense sunlight. According to Meredith Betterton, an applied-mathematics professor at the University of Colorado who has modeled them extensively, Americans are most likely to find them in the Rockies and the Sierra, where the high-altitude sun is brightest. As light hits any small dip in the snow's surface, it bounces off the sides, causing the bottom to melt fastest and creating a rapidly deepening trough. Sun cups are a mild nuisance, but since they rarely grow bigger than six inches across, they don't really hinder climbers or skiers. The same can't be said for a related phenomenon called penitentes. Mostly found high in the Andes, these occur when dips in the snow melt down so far that they leave columns of ice up to 30 feet tall. Named for their resemblance to praying monks, penitentes form only in very dry conditions, causing them to be hard as rock"an ice climber's dream," says mountaineer Todd Burleson, who has encountered massive penitentes on Everest's north side. "But the smaller ones," he says, "are a nightmare. To pass through them, you have to smack them with your ice ax and kick them out of the way." Now is that any way to treat a monk?