The Autumn Equinox 2025 will occur in just a few days, on Monday, September 22, 2025 at 4:20 PM Greek time. Specifically, the autumn equinox officially marks the arrival of fall in the Northern Hemisphere and by extension in our country. During the equinox, night and day have almost equal duration. Subsequently, in the Northern Hemisphere the day will shorten and night will lengthen, until the latter reaches its zenith at the winter solstice in December. The equinox occurs due to the tilt of Earth’s axis (23.5 degrees). As our planet orbits around the Sun, the rays fall differently in each season. During the equinoxes – both spring and autumn – the axis does not tilt toward or away from the Sun, resulting in light being distributed symmetrically. From antiquity to today, the equinox has been an occasion for festivals and ceremonies. The ancient Greeks associated it with Demeter and the myth of Persephone, who descended to Hades marking the coming of autumn. In many cultures, the equinox is celebrated as a moment of balance, renewal and preparation for winter.
What the autumn equinox signifies
The equinoxes – spring and autumn – determine the beginning of spring and fall, while the solstices – summer and winter – mark the start of summer and winter respectively. On the other hand, while astronomically spring begins with the spring equinox, in reality – as scientists studying the environment have found – due to climate change nature is entering its spring cycle earlier and earlier. The season of spring comes earlier and earlier on our planet, and nowhere is this as noticeable as at the North Pole and generally at high latitudes.
In Greece, the day of the equinox does not coincide with the day when there is exactly equal day and equal night. Equal day-equal night occurs only in areas located exactly on Earth’s Equator. In those located either above – like our country – or below the Equator, equal day-equal night occurs several days before or after the “equinox”.
The equinox occurs twice a year, when Earth passes through the intersection points of the ecliptic (Earth’s elliptical orbit) and the celestial equator. In astronomy these points are internationally symbolized by the letters γ and γ΄. At this specific moment the sun-earth line is perpendicular to Earth’s axis of rotation, resulting in day and night having equal duration at any point on Earth’s surface. The equinox occurs around March 21 and September 23. The name equinox comes from the Greek words equal and day, while the international equivalent name, equinox, comes from the Latin aequus (equal) and nox (night).
The names spring and autumn equinox are relative and refer to areas of the Northern Hemisphere, as on the corresponding dates in the Southern Hemisphere the seasons are opposite. At the two poles the equinox has no meaning, while at points on the Equator the equinox is constant.
The significance of the equinox in astronomy
In astronomy, equinox refers to the stellar day during which the center of the solar disk is located for equal time periods above and below the horizon of each place, meaning it traces equal arcs (day and night), and during which the sun’s rays fall vertically on the equator. The phenomenon is due to Earth’s revolution around the sun and the tilt of its rotation axis. As Earth revolves around the Sun and because its rotation axis is not perpendicular to the orbital plane, the duration of day changes. Twice a year Earth is positioned such that the sun’s rays fall completely vertically on the equator.
In many languages the corresponding term literally does not refer to the concept of equal day but equal night, mainly due to its Latin origin (Latin aequinoctium). The two equinoxes occur between the two solstices, the winter solstice and the summer solstice. The phenomenon of equinox occurs on all planets in every solar system that exhibit tilt of the rotation axis relative to the orbital plane.
