During an Equinox, what is passing the equinotical celestial equator?

During an Equinox, the Sun is what crosses the equinotical celestial equator. An Equinox occurs twice a year, around March 21 and September 23, when the Sun is positioned directly above the equator. This results in nearly equal durations of day and night across the globe.

At these points, the declination of the Sun is zero, meaning that it is neither north nor south of the celestial equator. The phenomenon signifies a balance in solar illumination between the Northern and Southern Hemispheres. During the equinox, it is the Sun's apparent motion that causes it to pass through this line in the celestial sphere, making it a significant event in the astronomical calendar and influencing various cultural and meteorological patterns.

Understanding this process highlights the importance of the relationship between Earth, the Sun, and celestial movements and how these events impact navigational practices and timekeeping throughout the year.