Earth Day is the largest, most widely celebrated, international environmental event. Learning about and protecting Earth is what Earth Day is all about. People all over the world celebrate our efforts to protect plants and animals and to clean up the world we live in. Most people celebrate Earth Day on April 22nd each year. In some countries, it is celebrated a month earlier on the vernal equinox(春分), which occurs on or around March 21st. Senator Gaylord Nelson of the United States founded Earth Day. Earth Day was first celebrated in the United States on April 22nd,1970. Across the United States, over twenty million people participated in the first Earth Day. The huge turnout(参加人数) for the first Earth Day made it the largest organized celebration in the history of the United States. The success of Earth Day helped influence the government of the United States to create stronger laws to protect the environment. On March 21st,1971,United Nations Secretary-General U Thant made Earth Day an international celebration.He spoke about it at a UN Peace Bell Ceremony in New York City. The United Nations Earth Day ceremony continues each year on the day of the vernal equinox, with the ringing of the UN Peace Bell at the very moment of the equinox.