Vladimirs' name-day

15 minutes ago my mother called and congratulated me with my name-day. Cool, I really didn't know about that all my 26 years)))) But I have a question. Yes, it is the day of Vladimir the Saint, which baptized Rus in the end of IX century. But... Why is it exactly on the 26 of July? Is it his birthday? I don't think so...
You know, this guy was a very interesting person. He was a bastard of his father Sviatoslav, who was the great warlord of ancinent Rus. And he got his father's nature. He was a savage warrior and heathen. His brother Yaropolk was killed by his normans mercenaries.
First of all as a new kniaz of Kiev Vladimir tried to make a pantheon of slavic pagan gods. Cool idea, of course. But it was too old-fashioned (Simpsons... Romans Already Did It). So he was disapointed by this idea because nobody had praised it. Alright... After that he invited delegates of three main religions: Christianity, Islam and Judaism. He really liked Islam (It is accepted 4 legal wifes and Vladimir liked it), but he faced one problem: Emperor of Bysantine did not agree. Vladimir wanted to complete his collection of wives by a byzantine princess to get a full house. But he should be a Christian... Damn! "Okay, I will baptize!" he said, and he married her and they lived happy and long. And baptized Rus because ... because it is necessary! The end.
This knyaz is also famous in Russian folklore as Vladimir the Red Sun, a justful and merciful knyaz of Kiev, the head of bogatyrs (heroes, champions) Dobrynia Nikitich, Alesha Popovich and Ilia Muromets.
If you know why the Vladimir's name-day is on the 26 of July, please write me or just tell me your version of this))))

Thank you and good luck!