I literally do not understand why May 2nd is not an official holiday. No, not because Osama died. Because today marks the 13th Anniversary of the Battle of Hogwarts.
Today, 13 years ago, countless people gave their lives in the Battle of Hogwarts in order to help Harry defeat the Dark Lord. Including Severus Snape.
Severus Snape died at 38, murdered by Lord Voldemort, who believed by doing so, he would become the true master of the Elder Wand. However, he was wrong, and Severus nearly died in vain. Luckily, Harry Potter witnessed the whole thing, and Severus was able to give his memories to him.
If he had not asked Voldemort to spare Lily, Harry would have died that night in Godric's Hollow. There would never have been a "Boy Who Lived" in the first place.
If he had not stopped Quirrell, Harry would have died in his first year.
If he hadn't felt so sorry for what he had done, Harry would not have been able to kill Voldemort.
Remember Severus Snape, the real hero. Always.