The Lunar Phases online science activity is provided by the Astrophysics Science Project Integrating Research and Education Web site, which is the educational outreach program of the HiRes Cosmic Ray Research Group at the University of Utah. This fascinating lesson utilizes an interactive lunar animation that allows students to learn how the moon's orbit around the earth affects how we see it. Although this concept may seem fairly straightforward, it can actually be somewhat confusing. This activity, though, does a good job of explaining and illustrating what is actually happening with the sun, earth, and moon at various times throughout the month. The entire lesson is also available in Spanish.