
The equinoxes are the only times when the subsolar point (the place on Earth's surface where the center of the Sun is exactly overhead) is on the Equator, and, consequently, the only times when the Sun is at zenith over the Equator. The subsolar point crosses the equator, moving northward at the March equinox and southward at the September equinox. The equinoxes are the only times when the solar terminator is perpendicular to the Equator. As a result, the northern and southern Hemispheres are equally illuminated.
However, the axes of an equatorial or ecliptic coordinate system may be defined so as to be aligned with the ecliptic and vernal equinox at a fixed point in time (or aligned with an average); therefore due to the Earth's axial precession and changes in orbital parameters, the Sun position during equinoxes in an equatorial or ecliptic coordinate system may slightly differ from the aforementioned idealized values.