Lots of tweets and blog posts circulating today about the 50th Anniversary of Fantastic Four #1. But why is today the day? It didn't roll off the presses today as some are saying, but August 8 is a very common date stamp found on copies of the book. Many newsstands would stamp or even hand-write the current date when they received a periodical, and those dates are a valuable look at the history of comics distribution.
That said, these dates don't offer us precision, because comics could often arrive at different locations around the country on various different dates. You'll see a copy of Fantastic Four 1 stamped August 3 below, and I've heard of various other dates in early August for the book. But August 8 (which was a Tuesday in 1961) is by far the most common date stamp to be found on the book, so by all means — celebrate Jack Kirby and Stan Lee kicking off the beginning of the Marvel Universe.