Get Ready for Mystery Class 2020*
  Mystery Class starts January 27, 2020. Get ready this fall by tracking changes in day length as the Earth revolves around the Sun. More...


How to Participate

Revolving Earth


Mystery Class is a global game of hide-and-seek. Follow photoperiod clues to search for ten secret sites around the world. Track sunlight to solve a mystery—and discover the reasons for seasons along the way.

*Please note: Our spring 2020 Mystery Class challenge is a replay of a previous year's challenge. You have open access to all of the season’s clues (Weeks 1-11). We will reveal the locations of the 10 Mystery sites on April 13, 2020.