The principle of dividing eggs in spring is based on the phenomenon that the direct point of the sun moves above the equator and the time between day and night is equal.

Expansion: It is a traditional folk custom to divide eggs in spring, usually at the vernal equinox. At the vernal equinox, the egg stands on a horizontal hard surface, so that its bottom is in contact with the desktop or ground. Because the shape and center of gravity of the egg itself are unstable, it may fall down at other times. However, on the vernal equinox, when the sun shines vertically on any point on the earth's surface, the shadow will deviate from 0 degrees to the north or south (noon), and the egg can remain upright.

Due to the influence of the earth's rotation trajectory and equatorial inclination, the equinoxes can be completely equal only in the area near the equator. For other regions, there may be some deviations.