There are many ways of dividing the four seasons of the year. Astronomical seasons, for example, use the solstices and equinoxes to divide the year, with spring beginning on the vernal equinox, summer beginning on the summer solstice, autumn beginning on the autumn equinox, and winter at the winter solstice. On the other hand, the meteorological seasons (in the northern hemisphere) are based on the annual temperature cycle, so spring will always start on 1 March, summer on 1 June, autumn on 1 September, and winter on 1 December.
However, the old names of the festivals of Midsummer, 21 June (in the northern hemisphere) and Midwinter, 21 December (in the northern hemisphere) tell us our ancestors counted the divisions of the year in quite a different way, according to the light of the Sun. The days of greatest darkness fall from Samhain to Imbolc, with Yule at the midpoint, giving us a solar winter. The days of greatest light fall from Beltane to Lughnasa, with the summer solstice at midpoint, giving us a solar summer; the old song tells us “Summer is a comin’ in” on May Day, or Beltane. The Irish call Lughnasa the first day of autumn.
The Craft defines the seasons as follows, which draws on the old ways of counting the year, and reflects the relationship of the Sun and Earth:
Winter – Samhain to Imbolc Eve
Spring – Imbolc to Beltane Eve
Summer – Beltane to Lughnasa Eve
Autumn – Lughnasa to Samhain Eve