For years, space physicist Robert Clauer would trek off to Greenland once or twice a year to gather data on the upper atmosphere. He would fly four or five hours in the back of a cold cargo plane to reach a site where he would sit for days in a trailer crowded with instrument displays. When he wasn't busy observing, he could step outside to admire the aurora borealis or watch a passing herd of caribou. The experience was rugged, and sometimes exhausting, but it satisfied his soul and his scientific curiosity.

Select from the choices above to read the entire article.