All over the web and in papers and on the bulletin board at my day job there are reminders to help you celebrate April 22nd as Earth Day. Here are some example links:
The April 22nd Earth Day is a truly American thing. Heaven forbid, we should unite with the rest of the world and recognize an Earth-Centered day within the timings of the Earth. Better to try to make it sometime around Easter. Even Canadians are a month late and a whole lot of common sense short. Why? Well, maybe because it was good politics for a senator. Here is that History. Which has April 22nd, 1970 as the first Earth Day.
The true International Earth Day is March 20th–most sensibly on the Vernal Equinox. Here is the Statement of the true founder of Earth day, John McConnell. In 1975, it was the Vernal Equinox which was proclaimed as Earth Day by then President Ford