Autumn officially begins, marking end of summer in Saudi Arabia

Dubai: The autumnal equinox has occurred in Mecca, marking the official start of fall season in Saudi Arabia, the entire Arab world and across the Northern Hemisphere, as the sun aligns directly over the equator and begins its apparent southward journey, Sabaq Arabic online daily reported.

Majid Abu Zahra, head of the Jeddah Astronomical Society, explained that the equinox results from the tilt of the Earth’s axis—approximately 23.5 degrees relative to its orbit around the sun—combined with the planet’s orbital motion.

On this day, the sun rises due east and sets due west, bringing nearly equal lengths of day and night—about 12 hours each. In middle latitudes, daylight is slightly longer than nighttime by roughly eight minutes, owing to the sun’s apparent size and atmospheric refraction, which lifts the sun slightly above the horizon. Variations in temperature, humidity, and air pressure also affect these measurements, making precise sunrise and sunset times down to the second difficult to predict.

Abu Zahra noted that the first day of fall can vary between September 21 and 24 due to subtle changes in the Earth’s axial orientation relative to the sun. The solar year lasts about 365.2422 days, whereas the calendar year is 365 days, requiring leap years to maintain alignment, which can produce minor discrepancies between calendar dates and equinoxes.

Following the equinox, the sun will appear to move southward at roughly half a degree per day, gradually shortening daylight in the Northern Hemisphere. This shift influences satellite orientation, solar panels, and communications systems, while migratory birds begin their journey south in search of warmer climates.

By October, the sun will rise from the southeast and set in the southwest, resulting in shorter days and longer nights. In the polar regions, the Arctic Ocean begins to freeze, while Antarctic ice starts melting, signalling the seasonal changes in the Earth’s climate system.

Abu Zahra said the 2025 fall season will last 89 days, 20 hours, and 43 minutes, until the winter solstice on December 21. “These phenomena illustrate how the tilt of the Earth’s axis and its orbit around the sun shape day length, night, and the changing of the seasons,” he added, highlighting the enduring accuracy of astronomical principles relied upon by scientists for millennia.