As the sun rises directly in the East and sets directly in the West around the Equinox, people worshipped the sun setting in the west and imagined a faraway Pure Land of Amitabha; and this was the precursor to higan.
春分と秋分は、太陽が真東から昇り、真西に沈むので、西方に沈む太陽を礼拝し、遙か彼方の極楽浄土に思いをはせたのが彼岸の始まりである。