This is a picture of Comet West. Comets are balls of ice and dust which orbit the sun. When they approach the sun, its heat vaporises some of the ice, and the pressure of its light and the solar wind blow the vapor back, forming the tail.
PtyS 106 is the course that talks the most about comets.
PtyS 403, PtyS 407, and PtyS 411 also partly deal with comets.
Some other places you can find information on comets include: