Astronomy Picture of the Day . ... Credit: NASA / MSFC Explanation: Could solar sailing become a future Olympic sport ? Nearly 400 years ago astronomer Johannes Kepler observed comet tails blown by a solar breeze and suggested that vessels might likewise navigate through space using appropriately fashioned sails . It is now widely recognized that sunlight does indeed produce a force which moves comet tails and a large, reflective sail could be a practical means of propelling a spacecraft. ...