Figure 4.1 http://apod.nasa.gov/apod/ap050104.html
Figure 5.2 http://feed25.photobucket.com/albums/c69/nikemoto2511/web200812/feed.rss
Figure 6.1 http://www.123rf.com/clipart-vector/spacesuit.html
Figure 6.1 http://www.123rf.com/clipart-vector/spacesuit.html