A planetwide celebration of our home that started on April 22, 1970 with a "Teach-In" organized by Gaylord Nelson to bring greater awareness to environmental concerns. It spread spontaneously to thousands of campuses and involved at least 20 million participants. Earth Day has become popular enough that politicians and corporate heads have started giving speeches on April 22. (President Bush tried it in 2005, but the Great Smoky Mountains thundered and rained him out. See Animism. )