Autumn equinox marks change of seasons in Oman

Muscat: Oman will witness the autumn equinox on Monday, marking the official astronomical start of the fall season as the sun aligns directly over the equator, resulting in nearly equal day and night across much of the globe.

While the equinox signals the shift to cooler months in many regions, several parts of Oman — including the capital, Muscat — have been experiencing hotter-than-usual temperatures in recent days, highlighting the contrast between astronomical definitions of the seasons and actual weather conditions.

Astronomical calculations show that the equinox will occur in Oman at 10:19 pm local time. In Muscat, the sun is expected to rise at 5:55 am, reach its zenith at 11:59 am, and set at 6:03 pm, giving a day length of approximately 12 hours and 8 minutes. The slight extension is due to atmospheric refraction, which makes the sun appear above the horizon before its actual rise and after its actual set.

The autumn equinox is one of two equinoxes that occur each year, the other being in spring. During these events, Earth’s axial tilt is such that the sun’s rays fall directly on the equator, creating nearly equal day and night across the planet. The phenomenon illustrates Earth’s tilt of 23.5 degrees and its orbit around the sun, which together produce the four distinct seasons.

Einas bint Saif al-Mahrouqiyah, a member of the Oman Astronomical Society, explained that the precise equal day and night phenomenon, known as “Equilux,” will occur in Oman on Sunday, September 28. On that day, sunrise and sunset will both be at 5:57, producing exactly 12 hours of daylight.

She further clarified that during the autumn equinox, the sun appears to shift from the northern hemisphere — which includes Europe, Asia, North America, northern Africa, and the Arctic — to the southern hemisphere, covering Australia, southern Africa, and South America. This marks the start of autumn in the north and spring in the south.

As a result, temperatures in the northern hemisphere begin to gradually decline as the angle of the sun’s rays decreases, reducing the intensity of solar energy received. At the same time, the equinox has unique polar effects: the sun will set for the first time in six months at the North Pole, beginning a half-year-long night, while it rises at the South Pole, initiating six months of continuous daylight. Autumn in the northern hemisphere will last about 90 days, ending with the winter solstice on December 21.

Al-Mahrouqiyah noted that the autumn equinox typically falls on September 22 or 23, when the sun rises due east and sets due west, providing a natural reference for orientation. On the equator, shadows disappear at noon in a phenomenon known as the “zero shadow day.”

She emphasized that observing such events provides valuable educational opportunities for students and researchers in Oman. A simple sundial can demonstrate shadow movement, helping students understand the relationship between the sun’s angle and the changing seasons. Such practical observations complement classroom studies in earth sciences and astronomy.

The autumn equinox, she concluded, is one of the four key astronomical milestones marking seasonal changes, alongside the spring equinox and the summer and winter solstices. While the equinoxes bring nearly equal day and night, the solstices represent extremes: the longest day in summer and the longest night in winter.