Khaberni said the President of the Jordanian Astronomical Society, Ammar Al-Sakaji, that astronomically, spring in the northern hemisphere begins on Friday, the current March 20, when the vernal equinox occurs precisely at 17:49:14 PM Jordan time.
Al-Sakaji explained that at this moment, the sun is exactly perpendicular to the celestial equator, and its astronomical coordinates, or what is known as "the right ascension, are exactly zero," with mathematical precision reaching one in one hundred thousand.
He clarified that the vernal equinox occurs when the sun crosses the celestial equator from south to north, which is an imaginary extension of the earth's equator onto the celestial dome, noting that if a person were standing on the earth's equator at that moment, then the sun would pass vertically over his head as it moves northward in the sky.
He mentioned that at the time of the equinox, the length of the night and day are nearly equal all around the world, although the perfect equality does not occur at the exact moment of the equinox, due to two main reasons namely the apparent disk of the sun, since the sun is not just a point of light but has a visible diameter, and due to the physics of the atmosphere and its phenomena of refraction and reflection and scattering.
Al-Sakaji added that the true equality between night and day in Jordan occurs a few days from the date of the equinox, explaining that this year, they actually equalize on the 17th of March, due to these physical and geometric phenomena.
He pointed out that the length of day begins to increase gradually after the vernal equinox in the northern hemisphere, until it reaches its peak at the summer solstice on June 21, which is nearly the longest day of the year.
He drew attention to the fact that what distinguishes the days of the two equinoxes, the vernal and the autumnal, is that they are the only time in the year when the sun rises exactly from the true east (90 degrees) and sets exactly in the true west (270 degrees) for all inhabitants of the earth, and this occurs because the tilt of the earth's axis relative to the sun is zero at that moment, meaning that the earth’s axis neither points towards the sun nor away from it.
He explained that the Earth is always tilted on its axis at an angle of about 23.5 degrees, but the orientation of this tilt relative to the sun on the day of the equinox makes its effect neutral.
Al-Sakaji pointed out that the right ascension is the celestial equivalent of terrestrial longitude lines, and is typically expressed in units of time (hours, minutes, and seconds) rather than degrees, with the possibility of conversion between them because the sky appears to rotate a full circle within 24 hours.
He indicated that the zero point of right ascension, or the astronomical moment of the vernal equinox, is the point where two important celestial paths intersect, namely the celestial equator and the ecliptic, or the apparent path of the sun through the sky, and when the sun crosses this point moving from south to north, spring begins astronomically in the northern hemisphere of the Earth.
He clarified that this point serves as the primary reference for the celestial coordinate system, and functions similarly to the Greenwich meridian, which represents the zero longitude line on Earth, and has historically been known as the "First Point of Aries."
Al-Sakaji mentioned that although the vernal equinox is always defined as the zero point of right ascension, its actual location in the sky slowly changes over time due to a phenomenon known as the precession of the equinoxes, resulting from the gradual change in the orientation of the Earth's axis of rotation.
He explained that there is a westward drift of the reference point at a rate of about 50.3 arc seconds annually, approximately one degree every 72 years, leading to its change in position among the constellations, where it was located in the constellation of Aries in ancient times around the year 130 BC, later moved to the constellation of Pisces, and is expected to enter into the constellation of Aquarius around the year 2600.
He added that the movement of this reference point also leads to changes in the coordinates of the stars over time, where the right ascension of stars near the celestial equator increases by about 3.1 seconds annually.
Al-Sakaji concluded by saying that on March 20 of this year at 17:49:14 PM Jordan time, the sun crosses the celestial equator heading north, beginning the astronomical spring journey in the sky of the northern hemisphere of the Earth, describing this moment as brief in cosmic time calculations but representing the beginning of a new season of light, warmth, and life on planet Earth.
It is expected that the beginning of Eid al-Fitr will coincide with the beginning of spring astronomically.
