The brightness or darkness of the sky depends on a combination of factors such as the position of the Sun, the weather, and the amount of particles or pollutants in the atmosphere. Let's explore some of the key reasons:

• Time of Day: The position of the Sun plays a huge role in how bright or dark the sky appears. During the daytime, when the Sun is high in the sky, its light is scattered by the atmosphere, making the sky appear bright. As the Sun sets or rises, the sky becomes darker because the Sun's light has to travel through a larger portion of the atmosphere, reducing the amount of light scattered to Earth’s surface. This causes a darker sky and longer shadows.

• Cloud Cover: The presence of clouds can significantly affect the brightness of the sky. On a clear day, sunlight is scattered throughout the atmosphere, making the sky appear bright. However, if there is a lot of cloud cover, the light is absorbed or reflected by the clouds, resulting in a darker or overcast sky. Thick clouds can block most sunlight, causing the sky to appear gray and dimmer.

• Weather and Storms: Storms often bring dark skies due to the presence of heavy, thick clouds that block out sunlight. This can create a gloomy atmosphere, especially just before or during a storm. After the storm has passed, the sky can look clearer and brighter.

• Altitude and Location: The altitude and location of where you are also affect the appearance of the sky. In mountainous areas, the sky might appear brighter or clearer due to less air pollution. In cities or industrial regions, the sky might appear darker or hazier due to smog or air pollution particles in the atmosphere.

The sky's brightness or darkness is mainly influenced by the Sun's position, cloud cover, and the presence of particles or pollutants. The dynamic nature of Earth's atmosphere means the sky is always changing in color and brightness throughout the day.