By Elizabeth Royte
How do chameleons change their colors?
— Burt Latham, Joplin, Missouri
Chalk it up to a bad case of the jitters. The chameleon's nervous system activates special skin cells called chromatophores, which contain pigments capable of moving either toward or away from the surface of the skin. The pigments that migrate closest to the surface determine its current color. Interestingly, only a handful of the 150-odd species of chameleons can deliberately blend in with their background. The rest change color for more mundane reasons: to impress a mate, warm themselves by donning a darker shade, or ward off predators. Deploying kaleidoscopic bursts of color to scare off — or simply turn off — hungry diners may sound counterintuitive, but as California chameleon breeder Linda Davison points out, "When you're a tiny jungle snack living among 12-foot-long mamba snakes, you've got to be creative."
I've heard that the Pacific Ocean's sea level is higher than the Atlantic's. How can this be?
— John Frederick, New York, New York
Not only is the Pacific Ocean about twice the size of the Atlantic, but it's also, on average, 20 centimeters higher. To an islander in the South Pacific, this can mean the difference between a flooded cabana and a dry bed. Sea level isn't an absolute, but merely an average of the changes in ocean level over time — as determined by a handful of variables, such as currents, wind, and tides. Most significant, however, is salinity. Due to higher evaporative rates, the Atlantic is saltier, denser, and thus slightly lower than the Pacific. As for what occurs at "transitional" zones such as off Cape Horn, where the Pacific and Atlantic collide, there's not much to see. The 20-centimeter discrepency, after all, is based upon measurements taken over some 95 million square miles of ocean. Columbia University oceanographer Arnold Gordon puts it this way: "If you're on a boat, it won't exactly feel like you're going uphill."
How come they don't stamp passports anymore?
— Luke Kania, Wallkill, New York
Well, "they" still do, depending on your destination, but generally speaking the practice is being phased out. And someday, alas, the officious bureaucrat pounding passports with busybodyish glee may be a thing of the past, the Bartleby the Scrivener of international travel. While there seems to be no hard and fast rule about stamping passports, the trend is definitely away from the time-consuming flourish — thanks largely to the sheer volume of international travel, the end of the Cold War, and innovations on the intelligence front. Border checks in European Union countries are becoming increasingly rare; advanced technology identifies airline passengers long before their flights land. In the United States, machine-readable bar codes do most of the heavy lifting, leaving customs officials merely to mark visitor passports with an uninspired date — and ignore returning residents' stamp pleas altogether. Which may be all for the better. "Frankly," concedes U.S. Immigration Service spokesperson Eyleen Schmidt, "we never had a pretty stamp anyway."
I'm baffled: How was Ayers Rock formed?
— M. McCabe, Virginia City, Nevada
Ayers Rock is a hulking monolith of sandstone — a mile and a half long and 1,143 feet high — that rises from the semiarid desert of Australia's Northern Territory. It's an anomaly, connected to neither a broader mountain range nor a long-ago volcanic eruption. Aborigines call it Uluru and consider it sacred, attributing its creation to the handiwork of ancestors. But to geologists, Ayers Rock is a rare formation known as a bornhardt. Like other well-known bornhardts, such as Georgia's Stone Mountain, Ayers Rock sits atop a trough in the earth's surface, a position that over time compressed the normally porous sandstone and made it almost completely weather-resistant. Simply put, Ayers Rock withstood 100 million years of erosion while everything around it crumbled into sand — reason enough to deserve our respect.
In the movie The Edge, Anthony Hopkins makes a "compass" by rubbing a paper clip on a silk shirt and then floating it, atop a leaf, in water. Does this work?
— C. Rogers, Akron, Ohio
Ah, the old silk shirt trick. While theoretically possible, screenwriter David Mamet took some liberties in crafting that scene. Twelfth-century Chinese mariners, who are credited with devising the first compass, would place a sliver of lodestone on a floating stick and watch it swivel into alignment with the poles. The magnetic field of a lodestone, however, is far stronger than the electric charge of a flimsy piece of staticky metal. Not only that, but a leaf would make a wobbly platform for our makeshift needle, and ripples in the water would render it practically useless — which may explain why Hopkins spent much of the movie lost in the bush.
|March is the month of the vernal equinox, when the Sun's projection crosses the equator and begins its long swing back into the Northern Hemisphere. This year, spring officially arrives at 2:55 P.M. eastern standard time on the 20th. Two days later, Mars, Saturn, and Mercury will form an isosceles triangle in the evening sky. March is one of the best times for viewing Mercury: For much of the month it will be visible at night along the western horizon. The fullMoon occurs on the 12th, with a partial lunar eclipse peaking at 11:20 P.M. eastern on the 13th. Just before dawn on the 18th is a good time to locate Uranus if you have a telescope; it will be in the southeast, three degrees south of Venus. David N. Schramm|
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