How Do Butterflies Fly and More Questions From Our Readers

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The rounded profile of a bird’s wing creates an airfoil, which generates lift and allows the bird to fly. But butterfly wings are flat. How do butterflies fly?

Robert Kacmarcik, Green Valley, Arizona

Flat-winged insects also generate lift by using their wings as airfoils, says Robert Dudley, research associate at the Smithsonian Tropical Research Institute and professor at the University of California, Berkeley. Briefly put, the flapping of their forewings creates a low-pressure vortex above the wings, and their hind wings help them turn. Butterflies are less efficient fliers than birds, flapping their wings at a greater angle into the oncoming air and producing much more drag per unit of lift. But their erratic flight helps them evade predators, including birds.

Why have the storms in Jupiter’s Great Red Spot raged continuously for 150 years or more?

Michael Landau, Rome, New York

Scientists haven’t definitively answered that question, but they expect NASA’s Juno spacecraft, which is due to begin orbiting Jupiter this July, to gather vital data. Generally, says Jim Zimbelman, geologist at the Center for Earth and Planetary Studies at the Air and Space Museum, storms in any planet’s atmosphere occur when air masses of different temperatures collide, and Jupiter’s interior generates tremendous heat. And because the solar system’s largest planet is made mostly of gases, there are no land forms to slow the wind. In the Great Red Spot, a storm bigger than Earth itself, winds blow up to 425 miles per hour. Recent images from the Hubble telescope suggest that the spot is shrinking, but don’t expect calm skies over Jupiter anytime soon.

Ozone up high is considered beneficial, yet near the ground it is considered a hazard. Why the difference?

Marysue Vidro, Columbia, Maryland

Ozone, no matter where it occurs or how it is created, is both protective and reactive, says Pat Neale, senior scientist at the Smithsonian Environmental Research Center. Most ozone is produced naturally in the stratosphere, where it filters damaging solar UV-B radiation before it reaches the earth’s surface. At ground level, ozone is generated when industrial emissions—specifically, oxides of nitrogen and volatile organic compounds—interact in the presence of sunlight, and it’s hazardous because it can harm living tissues. In human beings, exposure to high ozone levels can inflame the lining of the lungs, even causing scarring and boosting susceptibility to infection.

How do scientists measure water flow in rivers and streams?

Howard J. Hammer, Simi Valley, California

There’s actually a tool for that, called a V-notch weir, says Donald Weller, senior scientist at the Smithsonian Environmental Research Center. It’s a rectangular plate with a V-shaped opening at the top. Place one across the flow, and the water will back up behind it; once you measure that depth, you can use a mathematical formula to calculate the flow rate.

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