Autumnal Equinox. Summer Solstice. Vernal Equinox. When each season starts 2012 2013 first day of winter, spring, summer, fall. See chart below for the exact dates and times of the annual equinoxes and solstices.
Why do the seasons change? The four seasons are determined by shifting sunlight (not heat!) —which is determined by how our planet orbits the Sun and the tilt of its axis. On the summer solstice, we enjoy the most daylight of the calendar year. Seasons Calculator – Limoges, France years 2000–2049. Archaeoastronomy pinpoints equinox, solstice and cross quarter moments throughout the year.