The first season of Supernatural, an American fantasy horror television series created by Eric Kripke, premiered on September 13, 2005, and concluded on May 4, 2006 after 22 episodes. It focuses on brothers Sam and Dean Winchester as they track down their father, John, who is on the trail of the demon who killed their mother and Sam's girlfriend. During their travels, they use their father's journal to help them carry on the family business -- saving people and hunting supernatural creatures. Jared Padalecki and Jensen Ackles star as Sam and Dean, with Jeffrey Dean Morgan recurring as their father, John, and Nicki Aycox as the demonic Meg Masters. This is the only season to air on The WB Television Network, with all subsequent seasons airing on The CW Television Network, a joint venture of The WB and UPN.

Answer this question based on the passage: when was the first episode of supernatural aired? OK. Let's think. My stream of consciousness:
The important part for answering this question is: The first season of Supernatural, an American fantasy horror television series created by Eric Kripke, premiered on September 13, 2005, and concluded on May 4, 2006 after 22 episodes. The answer is September 13 , 2005.