In astronomy the Shubun is defined as being the moment the sun transits the autumn equinoctial point, namely, the very moment that the sun is considered to be positioned at 180 degree celestial longitude.
天文学では、太陽が秋分点を通過した瞬間、すなわち太陽の視位置黄経が180度となった瞬間を秋分と定義する。