The main reason for season date changes is the Earth's elliptical orbit around the Sun. The Earth's orbit is not a perfect circle, which means that the distance between the Earth and the Sun varies throughout the year. Additionally, the Earth's axis is tilted at an angle of about 23.5 degrees, which causes the amount of sunlight that reaches the Earth's surface to change throughout the year.
As the seasons change, many of us look forward to enjoying our favorite activities, sports, and holidays. However, have you ever wondered why the dates of the seasons seem to shift from year to year? In this blog post, we'll explore the reasons behind season date changes and what you need to know to stay on top of the changing seasons.
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.
Several factors contribute to the apparent changes in season dates: