Ahhh - an explanation! Apparently my calendar goes by "Universal Time".
The September equinox occurs at 03:09 (or 3:09am) Coordinated Universal Time (UTC) on September 23, 2010. It is also referred to as the autumnal or fall equinox in the northern hemisphere, as well as the spring or vernal equinox in the southern hemisphere (not to be confused with the March equinox). This is due to the seasonal contrasts between both hemispheres throughout the year.
The equinox will occur in the evening of September 22, 2010, for locations on US Eastern Daylight Time or further west. To find the September equinox date in other time zones or other years, please use the Seasons Calculator.
at 9:26 PM on Sep. 15, 2010