It’s been a good 40 years for Pink Floyd’s The Dark Side of the Moon. Even though it has been four decades now, the album is far from forgotten. In fact, this will be a grand ‘ole birthday year for the album, and believe us when we say that everyone’s celebrating. To celebrate the album’s 40th birthday, this Sunday, the band is treating fans to an online interactive event. Starting after midnight in England (or Saturday at 8 p.m. in EST), fans can stream the album in its entirety on the band’s website and are invited to share their personal memories, photos and comments about the album on Twitter under #DarkSide40. The website will keep track of the tweets and an image of the moon will darken accordingly. And that’s not all; Storm Thorgerson, the artist who designed the iconic prism artwork on the album cover, has created 14 new versions of his original cover that will be revealed on the band’s website over the next few months. And the icing on the 40th birthday cake is that the record is one of the 25 recordings selected for preservation in the Library of Congress’ National Recording Registry. Dark Side was the band’s first Number One album in the U.S. and stuck on the American charts for a staggering 741 weeks between 1973 and 1988.