We take for granted the common, invisible gas that's all around us. It keeps us alive, delivers our weather, puts the wind in our sails and enables birds like the beautiful red-tailed hawk in this photograph—a shot taken by Joe Halberstadt in Union County, Indiana, and shared with us—to stay aloft. I'm talking about air.
Because air keeps us all going, we put together a fun learning quiz on it—from its chemistry to how long humans can hold a lungful of it. We hope you will enjoy it. Just click on the START QUIZ button to begin and don't worry about your score. The second time you take it you'll get every question right!
I should add that when Joe Halberstadt sent us his hawk photo, he said that he had taken it almost by accident. He was actually watching and photographing ospreys, but then noticed the hawking flying by. It's a great reminder to keep your eyes open and your camera ready for surprises even when you're focusing on something else. Many thanks for the photo and the observation, Joe. —Craig Neff and Pamelia Markwood