sky

“the actual day of exactly 12 hours of daylight won’t occur until the 26th”

The Sky This Week, 2011 September 20 – 27 — Naval Oceanography Portal

The word "equinox" implies that the length of day and night are equal on the 23rd, but since the Sun isn’t a point source of light and we view it at sunrise and sunset through a refractive atmosphere the actual day of exactly 12 hours of daylight won’t occur until the 26th. From then until March 16 next year the nights will be longer than the days.

The Sky This Week, 2011 September 20 – 27 — Naval Oceanography Portal