The changing of the seasons is a natural phenomenon that occurs due to the Earth's tilt on its axis and its orbit around the Sun. The four seasons - spring, summer, autumn (or fall), and winter - are typically defined by specific dates, which are often referred to as the solstices and equinoxes.
While we often think of seasons beginning on the 21st of a month, the exact astronomical start times shift every year. This happens for several technical reasons: Meteorological Versus Astronomical Seasons | News season date changes
The dates of the seasons vary from year to year because the Earth's orbit is not a fixed, predictable path. The Earth's orbit is influenced by the gravitational pull of other planets, particularly Jupiter and Venus. This means that the Earth's position in its orbit and the tilt of its axis can vary slightly from year to year. The changing of the seasons is a natural
In the Southern Hemisphere, the seasons are reversed: In the Southern Hemisphere, the seasons are reversed:
The Evolution of Season Date Changes: Science, Culture, and Climate
A more subtle but equally important factor affecting astronomical season dates is the concept of apsidal precession . The Earth’s elliptical orbit itself slowly rotates over a period of about 112,000 years. This means that the point in the orbit where Earth is closest to the Sun (perihelion) slowly shifts relative to the seasons. Currently, perihelion occurs in early January, making Northern Hemisphere winters slightly milder. In about 10,000 years, perihelion will align with the September equinox, altering the length and intensity of the seasons themselves. While this does not change the date of the equinox on our calendar, it would change the orbital context of that date, potentially leading to a future where the calendar’s seasonal dates no longer accurately reflect the planet’s actual thermal seasons.