改元

• 天安三年四月十五（859年5月20日） 改元。

• 貞觀十九年四月十六（877年6月1日） 改元元慶。

出處

《易經·繫辭下》：「八卦成列，象在其中矣。因而重之，爻在其中矣。剛柔相推，變在其中矣。繫辭焉而命之，動在其中矣。吉凶悔吝者，生乎動者也。剛柔者，立本者也。變通者，趣時者也。吉凶者，貞勝者也。天地之道，貞觀者也。」與中國唐代貞觀年號出處相同。

貞觀年間要事

• 貞觀6年 (864年) - 富士山的

• 貞觀11年 (869年) - 貞觀地震

紀年

參考

• 日本年號索引

　• 其他使用貞觀年號的政權

• 同期存在的其他政權之紀年

　• 大中（847年正月－860年十月）：唐朝唐宣宗、唐懿宗之年號

　• 咸通（860年十一月－874年十一月）：唐懿宗、唐僖宗之年號

　• 乾符（874年十一月－879年十二月）：唐僖宗之年號

　• 羅平（860年二月－八月）：唐朝時期領袖裘甫之年號

　• 天啓（840年－859年）：南詔領袖勸豐祐之年號

　• 建極（860年起）：南詔領袖世隆之年號

　• 法堯（至877年）：南詔領袖世隆之年號

Change of era

• February 7, 859 : The new era name was created to mark an event or series of events. The previous era ended and the new one commenced in Ten'an 3, on the 15th day of the 4th month of 859.

Events of the Jōgan era

• 859 (Jōgan 1, 1st month): All New Year's festivities were suspended because of the period of national mourning for the death of Emperor Montoku.

• 864 (Jōgan 6, 5th month): Mount Fuji erupted during 10 days, and it ejected from its summit an immense quantity of cinders and ash which fell back to earth as far away as the ocean at Edo bay. Many people perished and a great number of homes were destroyed. The volcanic eruption began on the side of Fuji-san closest to Mount Asama, throwing cinders and ash as far away as Kai Province.

• 869 (Jōgan 10): Yōzei was born, and he is named Seiwa's heir in the following year.

• July 9, 869 (May 26, Jōgan 11). The 869 earthquake and tsunami devastates a large part of the Sanriku coast near Sendai.

• 876 (Jōgan 17, 11th month): In the 18th year of Seiwa-tennōs reign (清和天皇18年), the emperor ceded his throne to his five-year-old son, which means that the young child received the succession (senso). Shortly thereafter, Emperor Yōzei formally acceded to the throne (sokui).