Autumn
Explanation
The phenomenon of seasons is primarily caused by the revolution of the Earth around the Sun combined with the tilt of Earth's rotational axis (approximately 23.5°) relative to its orbital plane. This axial tilt ensures that the Northern and Southern Hemispheres receive varying intensities of sunlight at different times of the year, resulting in opposite seasons.Detailed Analysis:
- Seasonal Inversion: The seasons in the Northern and Southern Hemispheres are always reversed. When one hemisphere tilts toward the Sun, the other tilts away.
- Spring in the Northern Hemisphere: This period typically begins around the Vernal Equinox (March 20 or 21), when the Sun crosses the celestial equator moving northward. The Northern Hemisphere begins to warm up after winter.
- Autumn in the Southern Hemisphere: Simultaneously, the Southern Hemisphere begins to cool down as it transitions from Summer to Winter. Therefore, when it is Spring in the North, it is Autumn in the South.
Key Takeaway: Due to the Earth's axial tilt, seasonal cycles in the Northern and Southern Hemispheres are diametrically opposite; Spring in one corresponds to Autumn in the other.