Q) I noticed a mockingbird and a robin mating near my house. What was that all about?
Julie Herndon, Yorktown, Virginia
A) INTERSPECIES SHAGGING, more commonly known as hybridization, is fairly widespread in the avian worldbut it happens almost exclusively between birds of the same phylogenetic genus, such as golden-winged warblers and blue-winged warblers. It's pretty obvious why: For sparks to fly between bird species, they must be similar in size and conversant in each other's mating calls and rituals. In the case of your local love birds, robins and mockingbirds are not in the same genus, or even in the same family, the next classification grouping. And though mockingbirds, as their name suggests, may be able to mimic a robin's mating call, robins are typically one and a half times as heavy, making it unlikely that these two could make, well, a good fit. Therefore, says Patrick Burns, director of the Population and Habitat Program at the National Audubon Society, you've either witnessed some "seriously confused" creatures or overindulged in the electric Kool-Aid.
Q) How come the five major whirlpools in the worldCorryvreckan, Old Sow, Moskstraumen, Saltstraumen, and Narutoare all in the Northern Hemisphere?
George Herrera, Pompano Beach, Florida
A) INDEED, THE FIVE tongue-twisting pools you mention all do swirl north of the equator, but their existence there is the result of either maritime history or a geographical fluke rather than the laws of hydrodynamics. Whirlpools, which can range from 30 to 300 feet across, occur when a fast current, usually driven by strong tides, is forced through a narrow fjord opening or a strait, or between two coastal islands, where it reacts with an opposing forcesuch as a current from a river mouth or a sharp turn in an undersea channelthat alters its course. As the current gets shoved upward and pushed in another direction, it begins to spiral around the turbulence, forming a vortex. The requisite conditions (strong tides, narrow landmasses, and river mouths) are by no means exclusive to the Northern Hemisphere. In fact, according to David Frantantoni, an oceanographer at the Woods Hole Oceanographic Institute in Massachusetts, similar-sized vortexes exist south of the equator, but the five "major" whirlpools you've listed are simply better known. Why? For centuries, the vast majority of world shipping took place in the Northern Hemisphere, and thanks to harrowing real-life incidents and a few tall tales, these pools gained notoriety for the threat they posed to the maritime industry. Other pools, such as those known to exist off the coast of New Zealand and near the Strait of Magellan, were never named because by the time they were discovered they no longer posed a significant threat to the modern shipping industry's motorized vessels. Hey, nobody ever said fame was fair.
Q) Why are all the planets round? Since space is a vacuum, there should be no resistance, and therefore no friction to cause the rounding.
Bob Detmers, Hamilton, Montana
A) YOU'RE CORRECT; friction doesn't shape the planets. Rather, it's gravity that dictates their spherical shape. A planet has so much matter that its total gravitational force acts as though it emanates from the center, pulling the outside particles toward the massive core. And when everything on the outside is being pulled inward with identical force, a sphere is the only possible shape it can assume. Furthermore, the more massive the planet, the stronger its force of gravity. "On really big planets, the force is so strong that tall mountains would be flattened," says Myles Standish, an astronomer at NASA's Jet Propulsion Lab in Pasadena, California, "but on smaller planets, the force isn't as great, so very strong structures wouldn't crumble." Knowing that, you can bet that alpinists of the future will have their sights set on smaller planets like Mars, where the volcano Olympus Mons rises over 70,000 feet, more than two times the height of Mount Everest.