Tenchō (天長) was a Japanese era name (年号,,nengō,, lit. "year name") after Kōnin and before Jōwa. This period spanned the years from January 824 through January 834. The reigning emperors were Junna-tennō (淳和天皇) and Ninmyō-tennō (仁明天皇).
February 6, 824Tenchō gannen (天長元年): The new era name was created to mark an event or series of events. The previous era ended and the new one commenced in Kōnin 15, on the 5th day of the 1st month of 824.
Events of the Tenchō era
824 (Tenchō 1): This summer was entirely dry; and prayers for rain were offered by the Buddhist priest Kūkai, who is also known by the posthumous name, Kōbō-Daishi. Those prayers seemed to be answered when it did begin to rain sometime later.