This is an activity (located on page 131 of the PDF) related to sleep and circadian rhythms as well as space travel. Learners will discover how the light/dark cycle is dictated by the rotation of Earth. In addition, learners will examine the annual changes in the duration of light each day as the planet orbits the sun. Learners will also discuss the implications in the light/dark cycle for astronauts aboard an orbiting spacecraft. This activity can be enhanced by sharing the "Astronaut's Sleep" Podcast with learners (see related resource link). This resource guide includes background information and sample evaluation questions.