Fans asked to darken side of moon as Pink Floyd LP turns 40

Pink Floyd co-founder and musician Roger Waters performs during the last show of his ''The Wall'' tour on the Plains of Abraham in Quebec City, July 21, 2012.

NEW YORK (Reuters) - Pink Floyd's seminal stoner album "Dark Side of the Moon" is turning 40 on Sunday, and the band's website has developed an interactive feature whereby fans can help turn a specially designed moon on the site dark.

Starting after midnight Sunday in England (8:01 p.m. EDT on Saturday), fans are invited to play back the classic album on PinkFloyd.com, then tweet their memories, photos or other thoughts and comments using #DarkSide40.

The collective tweets will darken a side of the moon on the website, EMI Music said on Wednesday.

One of the best-selling albums of all time, released in the United Kingdom in 1973, "The Dark Side of The Moon" was Pink Floyd's first No. 1 album in the United States. It remained on the U.S. chart for 741 weeks between 1973 and 1988, and has spent 30 years on the UK charts.

Nearly as iconic as its ethereal compositions is the album cover artwork of a prism by Storm Thorgerson, who was tasked with turning out a "simple and bold" design.

Thorgerson and his current firm, Storm Designs, have created 14 exclusive new prism designs that will be unveiled over time on PinkFloyd.com in honor of the anniversary, and the designs will gradually form a celebratory poster that can be downloaded.

The most recent version of the album was released in September 2011.

(Reporting by Chris Michaud, editing by Jill Serjeant and Philip Barbara)