Before you accuse me of being a hard-boiled purveyor of scrambled mythological insanity, read on. The egg has always been a tasty symbol of springtime. It contains the promise of new life and rebirth. Christians give their children eggs on Easter, a springtime celebration that has obvious ties to death and rebirth. We mark the first day of spring by purely astronomical means.
Earth orbits the sun once a year.
We have seasons because our planet's axis of rotation is tilted about 23 degrees with respect to the path of its orbit. In the Northern Hemisphere, the summer solstice occurs in late June and marks the first day of summer. It happens when the north end of Earth's axis leans sunward. The sun's rays hit our hemisphere more directly. On the first day of winter, the winter solstice in late December, our hemisphere points away from the sun.