What are equinoxes and solstices?

The equinox and solstice are two phases of the year that mark the beginning of the seasons and are related to the Earth’s tilt and position relative to the sun.

The two solstices happen in June (20 or 21) and December (21 or 22). These are the days when the Sun’s path in the sky is the farthest north or south from the Equator.

A hemisphere’s winter solstice is the shortest day of the year and its summer solstice the year’s longest.

In the Northern Hemisphere, the June solstice marks the start of summer: this is when the North Pole is tilted closest to the Sun, and the Sun’s rays are directly overhead at the Tropic of Cancer. The December solstice marks the start of winter: at this point the South Pole is tilted closest to the Sun, and the Sun’s rays are directly overhead at the Tropic of Capricorn. (in the Southern Hemisphere the seasons are reversed.)

The equinoxes happen in March (about March 21) and September (about September 23). These are the days when the Sun is exactly above the Equator, which makes day and night of equal length.

So, in the Northern Hemisphere you have:

Vernal equinox(about March 21): day and night of equal length, marking the start of spring
Summer solstice (June 20 or 21): longest day of the year, marking the start of summer
Autumnal equinox(about September 23): day and night of equal length, marking the start of autumn
Winter solstice (December 21 or 22): shortest day of the year, marking the start of winter