On this day, 6,013 years ago, Jehovah said the famous words "let there be light," and the universe was created. October 23, 4004 BC (remember, there is no year zero) was the big date.
If you're a young-earth creationist, that is. And if you also think Archbishop James Ussher didn't make any math mistakes in his literal interpretation of Biblical history in his Annales veteris testamenti, a prima mundi origine deducti. And you can trust Archbishop Ussher -- he was an Anglican Biblical literalist, after all; technically a Protestant but still intellectually acceptable to Catholics.
If you take the Bible as the literal truth, today is fine day for celebration! Hat tip to PZ Myers, as if he needs any more.