The Lunar Reconnaissance Orbiter is a spacecraft orbiting the moon. The primary instrument on LRO for analyzing the moon’s radiation environment is the Cosmic Ray Telescope for the Effects of Radiation, or CRaTER. This educator guide includes lessons to introduce students to cosmic rays and their effects on humans. The four lessons are aligned to National Science Education Standards. 1. The discovery and nature of cosmic rays 2. How to detect cosmic rays 3. How cosmic rays affect humans 4. The Cosmic Ray Telescope for the Effects of Radiation