*what was so significant to Osamu Tezuka about this day?*I discussed this briefly with a fellow member of this site and it was found (through Wikipedia) that the first Astro Boy story was published in April of 1951 . . . so it might be the date of publication. The only other thing I managed to find out about it was at this site:

http://blog.weigy.com/2010/04/happy-birthday-astro-boy-tetsuwan-atom/

but this still does not come out and directly say that this was the exact day Tezuka published Astro. I'm curious to know what everyone else thinks, or if anyone knows more about it.