In order to be consistent and to make forecasting easier, meterologists divide the year into 4 seasons of 3 months each:
These seasons are known as meteorological seasons.
Astronomers and scientists on the other hand, use the dates of equinoxes and solstices to mark the beginning and end of seasons in a year.
Like meteorological seasons, there are 4 astronomical seasons in a year:
Equinoxes and solstices illustration
Seasons occur because of the 23.5 degree tilt of the Earth's rotational axis - around the June solstice, the Northern Hemisphere is titled towards the sun. This causes summer in the Northern Hemisphere. The Southern Hemisphere on the other hand, is tilted away from the sun and therefore, experiences winter. The opposite occurs around the December Solstice, when the Southern Hemisphere is tilted towards the sun, while the Northern Hemisphere is tilted away.
The solstices and equinoxes, on the other hand are caused by the Earth's orbit around the Sun.
March equinox: The March equinox occurs when the sun crosses the true celestial equator – or the imaginary line in the sky above the Earth’s equator – from south to north on a day between March 20 and 23. In other words, the Sun moves north of the Equator during the March equinox.
June solstice: The June solstice is also referred to as the summer solstice in the Northern Hemisphere and the winter solstice in the Southern Hemisphere. This is the time when the Sun is at its furthest point from the Equator and the Earth’s north pole tilts towards the Sun.
September equinox: The September equinox is also referred to as the autumnal, autumn or fall equinox in the Northern Hemisphere. It is known as the spring or vernal equinox in the Southern Hemisphere. It occurs on a day between September 21 and 24 when the Earth’s axis of rotation is perpendicular to the imaginary line connecting the centers of the Earth and the sun.
December solstice: The December solstice marks the beginning of winter in the Northern Hemisphere, and summer in the Southern Hemisphere. It also sometimes called the winter solstice in the Northern Hemisphere and summer solstice in the Southern Hemisphere. It occurs on a day between December 20 and 23. At this point, the sun appears directly above the Tropic of Capricorn, and the days are shortest at locations north of the Tropic of Cancer. South of the Antarctic Circle the Sun is visible 24 hours per day.
The Seasons Calculator shows the times and dates of Vernal (Spring) & Autumnal (Fall) equinoxes and Summer and Winter solstices all over the world.