Solstice vs Equinox: What's the Difference?

Four times a year the sun reaches a turning point: two solstices and two equinoxes. They mark the start of the seasons in many calendars. The difference comes down to where the sun sits relative to Earth’s equator.

First, why seasons happen at all

Earth’s axis is tilted by about 23.4 degrees. That tilt stays pointed in the same direction in space as Earth circles the sun, so over a year each hemisphere leans toward the sun for a while and away from it later. When your hemisphere leans toward the sun, the sun climbs higher, days are longer, and you get summer; when it leans away, you get winter. Distance from the sun barely matters — in fact Earth is closest to the sun in early January, during the Northern Hemisphere’s winter.

Equinoxes: day and night in balance

An equinox happens when the sun is directly above the equator. At that moment neither hemisphere is tilted toward the sun, so daylight and darkness are nearly equal — about 12 hours each — almost everywhere on Earth. The word means "equal night". There are two each year:

• March equinox (around 20 March) — spring begins in the north, autumn in the south.
• September equinox (around 22–23 September) — autumn in the north, spring in the south.

Solstices: the longest and shortest days

A solstice happens when the sun reaches its furthest point north or south of the equator. One hemisphere then has its longest day of the year and the other its shortest:

• June solstice (around 21 June) — longest day and summer in the north; shortest day and winter in the south.
• December solstice (around 21 December) — shortest day and winter in the north; longest day and summer in the south.

"Solstice" means "sun stands still" — around these dates the sun’s daily high point seems to pause and reverse direction.

How to remember it

Use the day length: an equinox is the balance point (equal day and night), while a solstice is an extreme (the most or least daylight). Between a solstice and the next equinox, days are steadily getting longer or shorter — which is exactly what a sun-times chart shows.

See the exact dates and times of this year’s solstices and equinoxes for your location — plus how your day length is changing right now — with the Sun Times tool. Planning around the weather too? Learn how to read a forecast.