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When do the year’s four seasons start—winter, spring, summer, and fall? It depends on who you ask! Also, the dates of the equinoxes and solstices can change from year to year. Learn more about the four seasons (and guess which of the four seasons is the shortest!).
When Do the Seasons Start?
The dates when the seasons begin and end vary depending on whom you ask. 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.
The meteorological start date is based on our 12-month civil calendar and the annual temperature cycle.
Note: The dates above correspond to the start of the listed seasons in the Northern Hemisphere. 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.
Here is a basic explanation of how astronomers and meteorologists define seasons differently:
The astronomical start of a season depends on the position of the Earth in relation to the Sun. More specifically, either a solstice (for winter and summer) or an equinox (for spring and autumn) marks the start of each season.
In contrast, the meteorological start of a season relies on the annual temperature cycle and the 12-month calendar. Each season starts on the first day of a specific month and goes on for three months. Spring starts on March 1, summer on June 1, autumn on September 1, and winter on December 1.
The Old Farmer’s Almanac is an astronomical “calendar of the heavens,” so our book has long followed the astronomical definition of the seasons based on the Sun and Earth!
What Causes the Seasons?
It’s commonly assumed that the warmer seasons happen because Earth is nearer the Sun (and the colder seasons happen when Earth is farther from the Sun). Nope.
It’s the Earth’s tilted axis that causes the seasons. The axis is always tilted in the same direction. So, as the Earth orbits the Sun over the 12 months of the year, different parts of Earth get the Sun’s direct rays. Learn more about the reason for the seasons.
Why Has the Date Changed for the Start of Seasons?
You may have noticed that the first day of spring is on a different date than when you were younger. The dates actually shift over time. Why? There are several reasons, but the one that’s easy to understand is that the Sun doesn’t follow a human calendar!
While our Gregorian calendar was designed to match the time it takes for the Earth to complete one orbit around the Sun, it’s not exact. Specifically, it eliminates leap days in century years not evenly divisible by 400, such as 1700, 1800, and 2100, and millennium years by 4,000, such as 8000 and 12000.
Therefore, the dates of the equinoxes and solstices can shift by a day or two over time, which causes the start dates of the seasons to shift over time, too.
Which Season is the Shortest?
It can sometimes feel like winter is dragging on forever, but did you know that winter is the shortest season of the year? (In the Northern Hemisphere, that is.)
Yes, the seasons are different lengths! 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 get closest to the Sun (perihelion), and in July, we get farthest away (aphelion).Read more about perihelion and aphelion.
When Earth is nearer to the Sun, its gravity is stronger, so our planet moves a little faster in its orbit. In the Northern Hemisphere, fall and winter are shorter because we move faster through space during that time of year. Conversely, Earth travels more slowly when it is farthest from the Sun, resulting in a longer spring and summer. (The opposite is true in the Southern Hemisphere.)
This is all to say that the seasons range in length from about 89 days to about 94 days.
The Four Seasons
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 first day of spring, the length of day and night is about the same, lasting around 12 hours each. This happens a few days before the official start of spring (vernal equinox) in the Northern Hemisphere. The Sun crosses the celestial equator going northward; it rises exactly due east and sets exactly due west.
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.
During the autumnal equinox, day and night are approximately equal in length, lasting around 12 hours each. In the Northern Hemisphere, the exact time of equal day and night occurs 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.
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 increases.
What’s your favorite season—and why? Let us know in the comments below!
Catherine Boeckmann loves nature, stargazing, and gardening so it’s not surprise that she and The Old Farmer’s Almanac found each other. She leads digital content for the Almanac website, and is also a certified master gardener in the state of Indiana. Read More from Catherine Boeckmann