Adust devil recently blew across the field and driveway where I live. A dust devil is a rotating wind mass -- a miniature tornado -- not too large, not too dangerous.

It appeared suddenly at the edge of our woods. It passed onto dry ground and picked up clay dust. As it whirled the dust into the air, I could easily see the outline of this tiny rotary wind.

I watched it make its way along the hillside and cross the gravel drive. As it did, there was no dust to pick up. The gravel was too heavy to lift. Suddenly, the little twister became invisible.

At the far edge of the driveway, it reappeared as it picked up new dust. It cruised down the hill and vanished at the edge of the woods.

Dust devils are like tornadoes. They are formed of rotating wind. In their dusty appearance, they look like the whirlpool of water that forms over a bathtub drain.

Most rotating windstorms form the same way. Warm air rises. As it rises, a low-pressure area forms. Wind flows from all directions toward the low pressure. As wind rushes in, the Earth's rotation gives it a spin.

As the air continues to rise and whirl, it can create enough force to lift things. A dust devil is so small it cannot lift much. We must protect our eyes, however, from the small particles it picks up.

Mars has an atmosphere thinner than on Earth. Mars is dusty as well. Flowing air on Mars creates dust devils like those on Earth.

On June 25, 2005, a dust devil passed close to the Mars rover "Spirit," which took its picture.

NASA has posted a picture of the dust devil, and a movie of it, on its Web site at http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20050819a.html.

Virginia's science Standards of Learning include wind and weather in units K-8, 1.7, 2.6, 4.6, 4.7, 5.7, 6.6, and ES-11.