Autumnal equinox

Japanese: 秋分 - しゅうぶん

Of the two points on the celestial sphere where the ecliptic intersects with the equator, the point where the sun crosses the equator from north to south is the autumnal equinox, which is the opposite point to the vernal equinox. The autumnal equinox occurs when the sun passes the autumnal equinox, in other words when the sun's ecliptic longitude reaches 180 degrees, and the day that includes the autumnal equinox is Autumnal Equinox Day. It is one of the 24 solar terms, and occurs around September 23rd of the solar calendar, during the eighth month of the lunar calendar. The autumn equinox is a total of seven days, three days before and three days after Autumnal Equinox Day, and Autumnal Equinox Day is the middle day of the equinox, making it a national holiday. The length of day and night are roughly equal on Autumnal Equinox Day, and from this day onwards, the days gradually become shorter and the nights longer in the Northern Hemisphere.

[Toshio Watanabe]

weather

When comparing temperatures at the autumnal equinox and the vernal equinox, in many places the temperature is more than 10°C higher than at the vernal equinox. Even though the astronomical conditions are the same, such a large difference appears due to the climatic conditions being an aftereffect from the previous season. It should also be noted that the autumnal equinox is also a time when mainland Japan is frequently hit by typhoons.

[Nemoto Junkichi]

[Reference] | Autumnal Equinox Day | 24 Solar Terms

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

天球上、黄道が赤道と交わる二つの交点のうち、太陽が赤道の北から南へ横切る点が秋分点で、春分点の対向点である。太陽が秋分点を通過するとき、つまり太陽の黄経が180度に達したときが秋分で、秋分を含む日が秋分の日である。二十四節気の一つで、陰暦8月の中、太陽暦の9月23日ごろにあたる。秋分の日の前後各3日、合計7日間が秋の彼岸(ひがん)で、秋分の日は彼岸の中日となり、国民の祝日である。秋分の日は昼夜の長さがほぼ等しく、この日を境として北半球では昼はしだいに短く、夜は長くなっていく。

［渡辺敏夫］