When do the seasons officially start?

There are four traditional seasons on Earth—spring, summer, fall (or autumn), and winter—and each is marked by the movement of the Sun in the sky. In the Northern Hemisphere, spring starts at the moment the Sun is directly over the equator, going from south to north, called the vernal equinox. Summer starts the moment the Sun is farthest north, called the summer solstice. Fall begins the moment when the Sun is directly over the equator, going from north to south, called autumnal equinox. Winter starts the moment the Sun is farthest south, called the winter solstice.