Autumnal Equinox in Jordan on Wednesday to End the Astronomical Summer
Amman4 min read
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The President of the Jordanian Astronomical Society, Ammar Al-Sakji, said that the moment of the autumnal equinox begins at dawn on Wednesday, announcing the astronomical start of autumn in the northern hemisphere of the Earth, and the beginning of spring in the southern hemisphere, and astronomical autumn lasts about 90 days.
The moment of this year's autumnal equinox occurs at 3:05 am on Wednesday, Jordan time, when the sun, in its apparent annual movement, crosses the celestial equator from north to south.
On the day of the equinox, the sun rises from a point very close to the geographical east and sets from a point very close to the geographical west.
Despite the common saying that the day and night are exactly equal on the day of the equinox, this is not accurate from an observational point of view, as the day is slightly longer than 12 hours.
This is mainly due to the refraction of light in the atmosphere, which makes the sun appear above the horizon while its geometric position is slightly below it, in addition to the calculation of sunrise and sunset times relative to the upper edge of the sun's disk rather than its center.
For Amman and its surroundings, the length of the day approaches 12 hours more significantly after the equinox for several days; on September 26, it is about 12 hours and one minute, while on September 27, it is about 11 hours and 59 minutes, so the closest observational equality between the length of day and night occurs approximately between these two dates.
The succession of seasons is not due to the change in the distance between the Earth and the sun, but to the tilt of the Earth's axis of rotation by about 23.4 degrees relative to the plane perpendicular to its orbit around the sun.
This tilt, along with the Earth's rotation around the sun, causes the angle of incidence of sunlight and the length of day and night to change throughout the year.
Evidence of this is that the Earth is closest to the sun during the winter in the northern hemisphere, in early January, and farthest from it during the summer in early July.
After the autumnal equinox, the sun begins to rise gradually for Jordan from locations located to the south of the east, and to set from locations located to the south of the west, while its altitude in the sky at noon decreases, and the hours of daylight gradually decrease while the hours of night increase.
This apparent movement continues until the winter solstice in December, when the sun reaches its maximum southern inclination, and the northern hemisphere of the Earth experiences the shortest day and longest night of the year.
The astronomical autumn of 2026 extends from the moment of the autumnal equinox at dawn on Wednesday, September 23, at 3:05 am Jordan time, until the moment of the winter solstice on December 21 at 11:50 pm, lasting about 89 days, 20 hours, and 45 minutes, approximately 90 days.
The lengths of the astronomical seasons vary slightly from year to year due to the elliptical nature of the Earth's orbit around the sun and the change in its orbital speed, as the Earth moves at different speeds along its orbit according to Kepler's Second Law.
The autumnal equinox is an astronomical opportunity to observe the relationship between the Earth's movement and what appears daily in the sky; it is possible within a few days to observe the change in the position of the sunrise and sunset and the decrease in the duration of the day, in an annual scene that reflects the effect of the Earth's movement around the sun and the inclination of its axis of rotation, and the Jordanian Astronomical Society will document these phenomena observationally.
