Space is not entirely black. In fact, it is filled with light. The reason it appears black to our eyes is because the vast majority of the universe is exceedingly cold. The coldest region, the cosmic microwave background, has a temperature of only about 2.7 Kelvin (-270.45°C). This means that the light emitted by objects in space is extremely faint. Our eyes are simply not sensitive enough to detect most of this light.

In addition, space is very empty. There are very few atoms or molecules in space. This means that there is nothing for light to interact with. As a result, light travels in a straight line in space. This means that the light from distant objects is not scattered or reflected towards our eyes.

However, there are some objects in space that are bright enough to be seen with the naked eye. These include the sun, moon, planets, and stars. These objects emit their own light, or they reflect light from other objects.