What is Earth Day? It has spread and is celebrated all over the world. Earth Day is a day designed to inspire awareness and appreciation for the Earth’s environment. It was founded by U.S. Senator Gaylord Nelson as an environmental teach-in held on April 22, 1970. Earth Day is celebrated in the spring in the Northern Hemisphere and autumn in the Southern Hemisphere. The U.S. Environmental Protection Agency (EPA) will hold free events for the public on the National Mall this weekend to celebrate the 40th anniversary of Earth Day. The events will feature interactive, fun and educational exhibits related to environmental protection.