Solstices & Equinoxes: When the Seasons Change
The exact dates of the seasonal changes in the Northern Hemisphere and why they happen.
What solstices are
Solstices mark the times of year with the greatest and least amount of sunlight. The summer solstice (June 21) gives the longest day, and the winter solstice (December 21) the longest night of the year.
They happen because Earth's axis is tilted about 23.4 degrees relative to its orbit, making the Sun reach its maximum and minimum northern or southern declination.
What equinoxes are
The spring (March 20) and autumn (September 22) equinoxes are the moments when day and night last almost exactly the same across the whole planet.
The word equinox comes from the Latin 'aequinoctium', meaning 'equal night'. They are the official astronomical signal of a seasonal change.
Follow them with UntilDay
You can follow each of these astronomical milestones with their live countdowns, including the exact times for the Northern Hemisphere and facts about how different cultures celebrate them.