A finely textured cloud leads to an informal investigation and a lively scientific debate over how it formed.

The return of sunlight in polar spring means ozone destruction above the Antarctic—and, in 2011, above the Arctic.

One of the most enduring mysteries in solar physics is why the Sun’s outer atmosphere, or corona, is millions of degrees hotter than its surface. Now scientists believe they have discovered a major source of hot gas that replenishes the corona.

Like a creature from a hydrologic horror flick, Devils Lake, North Dakota, has been expanding off and on for 70 years, most dramatically from the mid-1990s onward. Some of its tendrils have blocked rail lines and roadways for years.

Snowstorms have been a dime a dozen across much of the central and eastern United States over the last few months, but four of them got special scrutiny.