* Stars: The most obvious source of light in the night sky comes from distant stars. These are massive balls of hot gas that emit their own light. While each star is faint compared to our sun, the sheer number of stars in the universe makes them collectively visible as a faint glow.
* Airglow: This is a faint, natural light emitted by the Earth's atmosphere. It's caused by chemical reactions in the upper atmosphere, excited by solar radiation. Airglow is usually faint, but can sometimes be visible as a greenish glow.
* Light pollution: This is the most common reason why the sky appears brighter than it should. Artificial light from cities, towns, and streetlights scatters in the atmosphere, obscuring the faint light from stars and making the sky appear brighter.
So, the "brightness" of the night sky is largely due to the light sources we see, not the sky itself being bright. The true darkness of space is much more profound than what we typically experience on Earth.
