Here's why:

* Charged particles from the sun: The sun constantly emits a stream of charged particles called the solar wind.

* Interaction with Earth's atmosphere: When these particles reach Earth, they interact with the gases in our atmosphere, primarily in the upper layers.

* Excitation and emission: This interaction excites the atoms in the atmosphere, causing them to release energy in the form of light. This light appears as a glowing region in the sky, known as the Aurora Borealis (Northern Hemisphere) or Aurora Australis (Southern Hemisphere).

Let me know if you have any other questions!