Twice annually, the Earth experiences an equinox, an astronomical event occurring when the center of the Sun crosses the plane of the planet's equator. Derived from the Latin terms for "equal night," the equinox serves as a significant marker in human history, having been tracked by ancient civilizations alongside solstices.

During these events, the Sun shines directly over the equator at noon. Because the Sun illuminates both the Northern and Southern Hemispheres equally, the North and South Poles are simultaneously bathed in sunlight. In 2026, the March equinox is scheduled for March 20 at 14:46 UTC. The subsequent event will take place on September 23 at 00:05 UTC.

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While the term suggests perfectly equal day and night, atmospheric refraction and the Sun’s physical size prevent an exact 12-hour split. As the Sun rises and sets, the atmosphere bends its light, effectively adding several minutes of daylight to each day. Consequently, the date on which day and night are most balanced varies based on an observer's specific latitude.

The equinoxes also dictate seasonal transitions. The March event acts as a vernal equinox for the Northern Hemisphere, bringing warmer temperatures and longer days, while the Southern Hemisphere experiences the onset of autumn. By September, these roles reverse, with the Northern Hemisphere heading toward winter and the Southern Hemisphere moving into spring.

Source: NASA