1. The Vernal Equinox (March 20/21): This marks the beginning of spring in the Northern Hemisphere and autumn in the Southern Hemisphere. On the equinox, day and night are roughly equal in length across the globe. It's when the Sun crosses the celestial equator moving north.
2. The Summer Solstice (June 20/21): This is the longest day of the year in the Northern Hemisphere and the shortest day of the year in the Southern Hemisphere. The Sun reaches its highest point in the sky and the Earth experiences the most daylight hours.
3. The Autumnal Equinox (September 22/23): This marks the beginning of autumn in the Northern Hemisphere and spring in the Southern Hemisphere. Like the vernal equinox, day and night are roughly equal in length. The Sun crosses the celestial equator moving south.
4. The Winter Solstice (December 21/22): This is the shortest day of the year in the Northern Hemisphere and the longest day of the year in the Southern Hemisphere. The Sun reaches its lowest point in the sky, and the Earth experiences the least daylight hours.
These four days represent key points in the Earth's orbit around the Sun and the changing seasons. They have been celebrated and observed by cultures around the world for millennia.
