The New Bedford Whaling Museum was clearly onto something 20 years ago when it started the “Moby-Dick Marathon,’’ an annual event that celebrates Herman Melville’s epic novel by inviting a few hundred people to read passages out loud. Typically, the 135 chapters (plus epilogue) take about 25 hours to read. “Moby-Dick’’ is a big deal in New Bedford because part of the book, narrated by a sailor who wants to be called Ishmael, is set in the historic whaling city. But it’s a big deal elsewhere, too. Similar readings have sprung up in Mystic Seaport (Conn.) and Manhattan, and now an audio book has been developed with a slew of celebrity readers. Called “Moby-Dick Big Read,’’ the online version of Melville’s magnificent book was created by artist Angela Cockayne and writer Philip Hoare, who was one of the “Moby-Dick’’ readers in New Bedford in January. The audio book, available on iTunes and streamed on SoundCloud, features the likes of actor/comedian Stephen Fry, Pet Shop Boy Neil Tennant, actress Fiona Shaw, novelist Will Self, actor Benedict Cumberbatch (inset), playwright Tony Kushner, filmmaker John Waters, actor Simon Callow, Sir David Attenborough, British Prime Minister David Cameron, and Pulitzer Prize-winning poet Mary Oliver. The folks at the museum know all about the audio book and they approve. “We love the ‘Big Read, ’’ said Michael Lapides, director of digital initiatives at the museum. “It’s sort of the antithesis of what we do here because theirs is celebrity-based and we’re open to the public, but it’s still great. The more the merrier.’’