When do the four seasons—autumn, winter, spring, and summer—start? Here are your equinox and solstice dates for 2019 and 2020—plus, the definition of the astronomical season versus the meteorological season.
When Do the Seasons Begin?
Each season has both an astronomical start and a meteorological start. It sounds complicated, but trust us, it’s not! The astronomical start date is based on the position of the Sun in relation to the Earth, while the meteorological start date is based on the 12-month calendar and the annual temperature cycle. See below for a more in-depth explanation.
The First Days of the Seasons
Note: These times are based on Eastern time (ET). Subtract 3 hours for Pacific time, 2 hours for Mountain time, 1 hour for Central time, and so on.
|Seasons of 2019||Astronomical Start||Meteorological Start|
|SPRING||Wednesday, March 20, 5:58 P.M. EDT||Friday, March 1|
|SUMMER||Friday, June 21, 11:54 A.M. EDT||Saturday, June 1|
|FALL||Monday, September 23, 3:50 A.M. EDT||Sunday, September 1|
|WINTER||Saturday, December 21, 11:19 P.M. EST||Sunday, December 1|
|Seasons of 2020||Astronomical Start||Meteorological Start|
|SPRING||Thursday, March 19, 11:50 P.M. EDT||Sunday, March 1|
|SUMMER||Saturday, June 20, 5:44 P.M. EDT||Monday, June 1|
|FALL||Tuesday, September 22, 9:31 A.M. EDT||Tuesday, September 1|
|WINTER||Monday, December 21, 5:02 A.M. EST||Tuesday, December 1|
Astronomical Season vs. Meteorological Season
The astronomical start of a season is based on the position of the Earth in relation to the Sun. More specifically, the start of each season is marked by either a solstice (for winter and summer) or an equinox (for spring and autumn). A solstice is when the Sun reaches the most southerly or northerly point in the sky, while an equinox is when the Sun passes over Earth’s equator. Because of leap years, the dates of the equinoxes and solstices can shift by a day or two over time, causing the start dates of the seasons to shift, too.
In contrast, the meteorological start of a season is based on the annual temperature cycle and the 12-month calendar. According to this definition, each season begins on the first of a particular month and lasts for three months: Spring begins on March 1, summer on June 1, autumn on September 1, and winter on December 1. Climate scientists and meteorologists created this definition to make it easier to keep records of the weather, since the start of each meteorological season doesn’t change from year to year.
Because an almanac is an astronomical “calendar of the heavens,” The Old Farmer’s Almanac follows the astronomical definition of the seasons. However, we have listed both dates for each season above.
Why Do the Seasons Change?
We have the four seasons because of shifting sunlight (not temperature!)—which is determined by how the Earth orbits the Sun and the tilt of our planet’s axis.
As the Earth progresses through its orbit, the tilt causes different parts of the Earth to be exposed to more or less sunlight, depending on whether we are tilted towards or away from the Sun.
Photo Credit: NASA
Why Are The Seasons Different Lengths?
It can sometimes feel like winter is dragging on forever, but did you know that its actually the shortest season of the year? (In the Northern Hemisphere, that is.)
Thanks to the elliptical shape of Earth’s orbit around the Sun, Earth doesn’t stay the same distance from the Sun year-round. In January, we reach the point in our orbit nearest to the Sun (called perihelion), and in July, we reach the farthest point (aphelion). Read more about perihelion and aphelion.
When Earth is closer to the Sun, the star’s gravitational pull is slightly stronger, causing our planet to travel just a bit faster in its orbit. For those of us in the Northern Hemisphere, this results in a shorter fall and winter, since we are moving faster through space during that time of the year. Conversely, when Earth is farthest from the Sun, it travels more slowly, resulting in a longer spring and summer. (The opposite is true in the Southern Hemisphere.)
In other words, it takes Earth less time to go from the autumnal equinox to the vernal equinox than it does to go from the vernal equinox to the autumnal equinox.
Due to all this, the seasons range in length from about 89 days to about 94 days.
What defines each season? Below is a brief explanation of the four seasons in order of calendar year. For more information, link to the referenced equinoxes and solstices pages.
On 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. See our First Day of Spring page.
On the summer solstice, we enjoy the most daylight of the calendar year. The Sun reaches its most northern point in the sky (in the Northern Hemisphere) at local noon. After this date, the days start getting “shorter,” i.e., the length of daylight starts to decrease. See our First Day of Summer page.
On 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. See our First Day of Fall page.
The winter solstice is the “shortest day” of the year, meaning the least amount of sunlight. The Sun reaches its most southern point in the sky (in the Northern Hemisphere) at local noon. After this date, the days start getting “longer,” i.e., the amount of daylight begins to increase. See our First Day of Winter page.
What’s your favorite season—and why? Let us know in the comments below!