Today, September 22 2013, is the date of the Southward Equinox. This is the day where the Earth axis is inclined neither away from nor towards the Sun. The term equinox can also be used in a broader sense, meaning the date when such a passage happens. The name "equinox" is derived from the Latin aequus (equal) and nox (night), because around the equinox, night and day are about equal length.
More information about the Equinox can be found on the WIKI page Equinox
Kind regards,
Clemens