Why isn't the day of equal day/night the same day as the Vernal Equinox in 1997 from New York?

Here are the rising and setting and day length times around the Equinox at two latitudes: 

                     Rise             Set          Length
March 15th    +40    5:45           18:34           12:49
              +50    5:42           18:37           12:55
March 19th    +40    5:38           18:38           13:00
              +50    5:33           18:44           13:11
March 23rd    +40    5:32           18:42           13:10
              +50    5:24           18:50           13:26
The equinox happened on March 20, but the date when there are equal hours of day and night is set by the observers latitude and does not fall exactly on this date unless you are at the equator.
Copyright 1997 Dr. Sten Odenwald
Return to Ask the Astronomer.