The autumnal equinox is actually a national holiday in several countries.
Many people in Japan are celebrating a Buddhist holiday called Higan, which begins three days before the autumnal and vernal equinoxes and ends three days after. During that time, residents clean the tombstones and offer flowers at the graves of loved ones and hold family reunions.
Elsewhere, the Chinese, Koreans, and Vietnamese celebrate the equinox with moon festivals. Iranians celebrate a Persian autumn festival called Jashne Mihragan, which means friendship or love. And the traditional harvest festival in the United Kingdom is celebrated in conjunction with the harvest moon.
Here in the US, it's simply TGIF.
