Wikipedia explains the event this way:
The National Day of Prayer (36 U.S.C. § 119) is an annual day of observance held on the first Thursday of May, designated by the United States Congress, when people are asked “to turn to God in prayer and meditation”.
Fortunately — man, talk about your happy coincidence! — there’s also a National Day of Reason on the same day. I say fortunate not only because a federal judge declared the National Day of Prayer unconstitutional …
On April 15, 2010, Judge Crabb ruled that the statute establishing the National Day of Prayer was unconstitutional as it is “an inherently religious exercise that serves no secular function.” Judge Crabb also stated in her opinion, “If the government were interested only in acknowledging the role of religion in America, it could have designated a ‘National Day of Religious Freedom’ rather than promote a particular religious practice.” [Suckily, the decision was overruled on appeal.]
There were several suggestions following my International Atheist Blood Drive post, that the thing should really be held on the National Day of Reason, May 3, instead of the way-too-soon-to-organize-by Darwin’s Birthday, Feb. 12. And I agree. Now, if only some fiercely energetic and massively organized individual were to run with the idea, she (hey, you know it’s going to be a woman, right?) would have my wholehearted admiration. And I would damned sure donate.
But the REAL significance of May 3, to a superhero fanboy anyway, would be that, on the stroke of midnight (meaning it starts on the first minute of May 4), at theaters all over the nation, those of us who have a deep and abiding faith in Stan Lee and Marvel Comics, will be able to see this: