Imbolc (say it "ih-molg") is the astronomical cross-quarter between the Winter Solstice and the Spring Equinox. In Ireland it is called St. Brigid's day -- St. Brigit of Kildare, that is.
ancient ancestors divided each golden year into "pieces of eight", as
it were. They marked and celebrated the ongoing life and the cycle of
the seasons. Don't put too much stock in self-styled neo-pagan (read
"Victorian") trappings draped on solid archaeo-astronomy.
2013, the spring cross-quarter actually occurs 3 February at 15:57
UTC. Its actual date varies because of the vagaries our leap-year
As a result, celebration of the cross-quarter varies
by culture. In Ireland, St. Brigid's day is the First of February. In
Asia, the new moon following the spring cross-quarter is the start of
the new year (e.g., Tet in Vietnam).
At our house, we
celebrate the cross-quarter on Groundhog Day. After all, the
cross-quarter is the original reason for the hooplah this morning in
Punxsutawney, Pennsylvania, USA.