关于这张图
A small level is used to see if the trail is tilted upward or downward. In most cases where a rock has moved, the trail is tilted very slightly uphill, but the interns don't think this has a noticeable effect on the movement. The compass is included for scale. Photo credit: NASA/GSFC/Leva McIntire/LPSA intern To read a feature story on the Racetrack Playa go to: <a href="http://www.nasa.gov/topics/earth/features/roving-rocks.html" rel="nofollow">www.nasa.gov/topics/earth/features/roving-rocks.html</a> <b><a href="http://www.nasa.gov/centers/goddard/home/index.html" rel="nofollow">NASA Godda…
