KATAOKA Ryuho1, YAMAMOTO Kazuaki2, FUJIWARA Yasunori3,
1 Department of Polar Science, School of Multidisciplinary Sciences,
Nihon-shoki, red sign, pheasant’s tail, fan-shaped aurora, comet
The oldest record of an astronomical phenomenon in Japan was recorded in the Nihon-shoki as follows: “On December 30 in 620, a red sign appeared in heaven. The length was more than 1 jo (10 degrees). The shape was similar to a pheasant tail (Suiko-Tennou, 28)”. The appearance of a red sign has been recognized as an expression of a bad omen in literature, while it has been interpreted as the northern lights in geophysics. First we examine the description of the pheasant tail in detail. We then introduce the latest scientific findings that the northern lights show a fan-shaped appearance with a red background when appearing over Japan. After showing that the fan-shape is similar to a pheasant tail, also pointing out the low possibility of comets, we conclude that the oldest record of the red sign is consistent with the appearance of the northern lights over Japan. We hope that this examination contributes to increasing awareness of the sensitivity of Japanese people 1400-years-ago who compared a beautiful behavior of birds with a magnificent and rare natural phenomenon.