01 What is the vernal equinox?

Equinox – Wikipedia

The vernal equinox is an important reference point in astronomy, especially in the geocentric equatorial coordinate system. By definition, it is infinitely far away. The direction to it is therefore the same from any point in the Earth’s orbit. Because of precession, the vernal equinox moves steadily westward on the ecliptic, taking about 25,800 years to complete a full cycle.

Like the autumn point, the vernal equinox is a point of intersection of the celestial equator with the ecliptic – the apparent path of the Sun through the fixed star sky as seen from Earth.

The Earth’s axis is then exactly perpendicular to the line connecting the centers of the Earth and the Sun, and the equinox occurs on Earth.