1. Inverse square law of light: The intensity of light decreases with the square of the distance from the source. This means that if you double the distance between an object and a light source, the amount of light reaching the object will be four times less.

2. Atmospheric scattering: As light travels through the atmosphere, it is scattered by molecules and particles in the air. This scattering causes the light to spread out, which reduces the amount of light that reaches an object. The more air that light has to travel through, the more it will be scattered, and the dimmer the object will appear.

3. Absorption: Some of the light that travels through the atmosphere is absorbed by molecules and particles in the air. This absorption also reduces the amount of light that reaches an object.

4. Earth's curvature: The Earth's surface is curved, so the light from an object that is far away has to travel a greater distance to reach our eyes. This means that the light has more time to be scattered and absorbed, which makes the object appear dimmer.

The combination of these factors causes objects to become dimmer with distance.