As another comment points out: that's nothing compared to high energy/particle physics! The Pierre Auger Observatory certainly is a large collaboration for the

As another comment points out: that's nothing compared to high energy/particle physics! The Pierre Auger Observatory certainly is a large collaboration for the astroparticle physics domain though. It's a big international collaboration. Quick anecdote: my name (S Mueller) is not on that paper's author list because we had a rule that you had to be in the collaboration for a year before getting authorship. You stayed on for a year after leaving. Very reasonable! At the time I was nonetheless a bit bummed about missing out on the big Science paper. I guess I'm on the retraction though ;)