Here's why:
* Earth's Tilt: Earth's axis is tilted at approximately 23.5 degrees. This tilt means that different parts of the Earth receive varying amounts of direct sunlight throughout the year.
* Summer and Winter: When the Northern Hemisphere is tilted towards the sun, it experiences summer because it receives more direct sunlight and longer days. At the same time, the Southern Hemisphere is tilted away from the sun and experiences winter. The opposite occurs six months later when the Southern Hemisphere is tilted towards the sun.
* Spring and Autumn: The periods between summer and winter are spring and autumn, when the tilt of the Earth is more moderate, resulting in more equal day and night lengths and less extreme temperatures.
Other Factors:
While the tilt of Earth's axis is the primary cause of seasons, other factors also contribute:
* Earth's Orbit: Earth's elliptical orbit around the sun means that it's slightly closer to the sun in January than in July, but this effect is minor compared to the impact of the axial tilt.
* Latitude: Locations closer to the equator experience less variation in seasons, while locations further from the equator experience more extreme variations.
In summary: The tilt of Earth's axis is the primary factor responsible for the changing seasons, leading to variations in the amount of sunlight received at different locations throughout the year.