Forty-two years ago, one American politician had an idea he thought could put the issue of the environment on the national and international political agenda. A nation-wide teach-in, in the spirit of student protests against the Vietnam War, would show politicians that the people wanted to do something about the environment. Today, Earth Day has become the most widely celebrated secular holiday the world over.While speaking to an environmental conference in Seattle in September 1969, US Senator and former governor Gaylord Nelson of Wisconsin announced his vision for an environmental teach-in the following spring. He later wrote that the had begun developing the idea some seven years earlier, which resulted in his initiation of a presidential conservation tour with former US president John. F. Kennedy. His attempts to politicize the issue, however, did not bear fruit in those first years.In various articles and speeches on the issue, Gaylord recounts his frustration that the issue was important to the people but politicians were not paying attention. “The environmental issue simply was not to be found on the nation's political agenda,” he later wrote.In 1969, the US Senator proposed the idea of a teach-in to raise the issue’s prominence and the attention it was being paid. He later recalled, “if we could tap into the environmental concerns of the general public and infuse the student anti-war energy into the environmental cause, we could generate a demonstration that would force this issue onto the political agenda. It was a big gamble, but worth a try.”News of the event and enthusiasm to organize it spread quickly ahead of the day chosen, April 22, 1970. As a result, some 20 million people in the United States participated in events marking the first-ever Earth Day.The event, which started as a teach-in centered in American universities began to spread beyond the borders of the United States as attention and interest in the issue became stronger throughout the world and in international institutions. Twenty years after the US teach-in, the events spread to 140 countries with millions more participating each year. After 30 years, in 2000, hundreds of millions of people in 184 countries participated in Earth Day events, raising awareness of and advocating for the environment. Giving the event even more weight and cementing it into the world agenda, the United Nations voted to designate April 22 as “International Mother Earth Day.” In 2010, on its 40th anniversary, the number of worldwide participants in Earth Day grew to a billion, organizers estimated.In Israel, where environmental issues have been on the agenda for over a decade, events have been held across the country for several years. Most noticeable to the public is the initiative that involves municipalities and their residents turning off all lights for an hour on the evening of Earth Day both to save electricity and raise awareness. The most astounding element of the story of Earth Day is the way it has grown organically as a bottom-up movement. “Earth Day worked because of the spontaneous response at the grassroots level,” initiator Gaylord Nelson reflected. “That was the remarkable thing about Earth Day. It organized itself.”Just as the events marking Earth Day have grown organically throughout the years, so have the issues it attempts to highlight and bring into the limelight. While the first Earth Days in the 1970s focused on pollution in rivers and lakes, later shifting to the O-Zone layer and sea life preservation, today the focus has shifted on renewable energy, global warming and sustainability.This year, events will take place in various cities throughout the world and in Israel, with the participation of hundreds of millions of people. In Israel, while events were scheduled to take place in nearly two dozen cities throughout the country, the main event was to be held in Tel Aviv’s Rabin Square, along with the hour-long blackout that will be observed in the participating municipalities.