序 — 物の哀れ

A calendar that watches instead of counts.

Old Japan divided the year into twenty-four solar terms, and each of those into three kō — seventy-two microseasons, each about five days long. Their names are not dates but observations: the east wind melts the ice; rotten grass becomes fireflies; bears retire to their dens.

The list came from China; in 1685 the court astronomer Shibukawa Shunkai rewrote it to match what actually happens in Japan — which flowers open, which birds arrive, when the frost truly ends. It has been quietly correct ever since.

Mono no aware is the feeling this calendar is built from: a gentle sadness that things pass, and a sharper attention because they do. This page reads your date, finds its kō, and dresses for it. Come back in five days and it will be another season.