Here's why:

* The Sun's Energy: The sun is the primary source of energy for Earth. It provides the heat and light that drive many processes on our planet.

* Atmosphere: The sun's energy heats the atmosphere, causing air to circulate, creating winds, and influencing weather patterns.

* Hydrosphere: The sun's energy drives the water cycle. It evaporates water from oceans, lakes, and rivers, creating clouds, and ultimately causing precipitation.

* Surface: The sun's energy warms the Earth's surface, impacting plant growth, soil temperature, and the formation of glaciers and ice sheets.

Therefore, the sun plays a crucial role in driving external processes in the atmosphere, hydrosphere, and at the Earth's surface.