Q) A keen-eyed human sees 20/20. By that measure, how well can eagles see?
A reader with desert hiking in his future asks what fabric will keep you cooler in hot weather: cotton, which retains sweat, or a high-tech synthetic that wicks it away? Admirers of both materials have their own strong opinions, but the textile scientists we talked to said cotton and high-tech fabrics perform about the same during exercise in warm conditions. In a 2001 study from Indiana University's Human Performance Laboratory, eight "well-trained males" wearing cotton and evaporative synthetics were monitored as they walked and ran in moderately dry 85-degree air. No difference was found in the subjects' core temperatures. So it really comes down to comfort: The whole idea behind those technical garments is to keep you dry, which is the right strategy for Central Park but not ...
Robert Selzer, New Haven, Connecticut
A) If you could ask very nicely and get a bald eagle to sit in front of an eye chart, his score would probably be about 20/8, two and a half times better than a human's. Such is the visual acuity of the wedge-tailed eagle, which scientists have tested; in real terms, it means a small object we can spot from ten feet away can be detected by this bird from 25 feet. Eagles' sharp eyesight comes partly from optic lobes and eyeballs that are, in relative terms, significantly bigger than a mammal's, says Graham Martin, professor of avian sensory sciences at England's University of Birmingham. Their larger peepers also contain much more densely packed cones in the fovea, the area in the retina that sharpens imagespicture a high-end camera using finer-grain film. To top it off, you and I have only one fovea in each eye, and an eagle has two. No wonder they look so proud.
Q) Where do human beings live the longest lives, and what's their secret?
George Chiu, Walnut Creek, California
A) For centuries there have been tales of longevity-boosting Shangri-Laslike the Hunza region of Pakistan, the Vilcabamba area in Ecuador, and Georgia's Caucasus Mountainswhere people live to 130 or 140. Sadly, these appear to be myths, perhaps attempts to bring some areas renown and/or tourist dollars. But if the Fountain of Youth doesn't exist, there are places where people have a higher chance of reaching 100. According to Boston University's Tom Perls, a medical expert on aging, the top three are the Japanese island of Okinawa, Nova Scotia, and Sardinia. Scientists can't explain why these areas spawn healthier oldsters, but it may have to do with a more active, agrarian lifestyle, a diet rich in fish, and lower daily calorie counts. Still, you never know. The longest documented human life belonged to a woman from a country where diets are rich in richness: France's own Jeanne Louise Calment, who expired in 1997 at age 122.
Q) What would happen if we lost our moon?
Amanda Carlson, Dakota, ILlinois
A) Rest assured, there's no reason to fear that this may happen. But for the sake of argument, if the moon were to go AWOL, life on earth would become a different ballgame. Neil Comins, an astrophysicist at the University of Maine, says the oceans' tides would immediately become a third as strong, severely threatening life in the intertidal zone. This could also affect fish like the grunion, which spawn according to tidal changes. Sea turtle hatchlings, which use moonlight to find their way to the ocean, would be in trouble. But the most profound effect over the long haul would be the changes in the earth's obliquitythe angle of its spin axiswhich is stabilized by the moon's gravitational pull. Says NASA astrobiologist Kevin Zahnle, over millions of years the planet would wobble chaotically, which could mean ice caps in Miami. As if moonless walks on the beach weren't unromantic enough.