Fall equinox occurs today at 04:21HST. Today there will be little difference between the length of the night compared to number of daylight hours. This is the first day of fall as marked by many cultures in the northern hemisphere.
This year many calendars will mark September 23rd as the beginning of fall, and so it is for much of the world. Here in Hawaiʻi the equinox actually occurs on the 22nd when considering the time zone differences.