Explore how daylight changes in your part of the world as the Earth revolves around the Sun. Share and compare observations with people around the globe. Begin recording daily sunrise and sunset times. As students examine the sunrise/sunset data, have them calculate changes in photoperiod.

• Report your photoperiod: At least once each month, report your photoperiod to the real-time map.

• Ask Questions: How do students explain the changes in day length? Their explanations will reveal what they know—and what they are ready to discover—about the relationship between sunlight and seasonal change.

Photoperiod is the length of time between sunrise and sunset.