The Seasons

First Day of Spring - Spring Equinox - March 20th

On the first day of spring—the vernal equinox—day and night are each approximately 12 hours long (with the actual time of equal day and night, in the Northern Hemisphere, occurring a few days before the vernal equinox). The Sun crosses the celestial equator going northward; it rises exactly due east and sets exactly due west.

The Vernal Equinox

Ah, spring! This season brings increasing daylight, warming temperatures, and the rebirth of flora and fauna.
The word equinox is derived from the Latin words meaning “equal night.” Days and nights are approximately equal everywhere and the Sun rises and sets due east and west.
At the equinoxes, the tilt of Earth relative to the Sun is zero, which means that Earth’s axis neither points toward nor away from the Sun. (However, the tilt of Earth relative to its plane of orbit, called the ecliptic plane, is always about 23.5 degrees.)


First Day of Summer - Summer Equinox - June 21st

The first day of summer—the summer solstice—is the longest day of the year, the Sun reaches its most northern point in the sky at local noon. After this date, the days start getting shorter.

The Summer Solstice

Each year, the timing of the solstice depends on when the Sun reaches its farthest point north of the equator.

The word solstice is from the Latin solstitium, from sol (sun) and stitium (to stop), reflecting the fact that the Sun appears to stop at this time (and again at the winter solstice).


First day of Autumn - Autumn Equinox - September 22nd

On the first day of fall—the autumnal equinox—day and night are each about 12 hours long (with the actual time of equal day and night, in the Northern Hemisphere, occurring a few days after the autumnal equinox). The Sun crosses the celestial equator going southward; it rises exactly due east and sets exactly due west.

It is the summer's great last heat,
It is the fall's first chill: They meet.
–Sarah Morgan Bryan Piatt

The Autumnal Equinox

The word equinox comes from the Latin words for "equal night." The fall and spring equinoxes are the only days of the year in which the Sun crosses the celestial equator.
From here on out, the temperatures begin to drop and the days start to get shorter than the nights.

First Day of Winter - Winter Equinox - December 21st

The start of winter—the winter solstice—is the shortest day of the year, when the Sun reaches its most southern point in the sky at local noon. After this date, the days start getting longer.

The Winter Solstice

Winter inspires both joy and woe. Some people can't wait for the cooler weather, snow, skiing and ice skating, curling up by a fire, and the holiday spirit. Other people dislike the frigid temperatures, blizzards, and wild weather.