* Clouds: Clouds can block the sun's rays, even during the day.

* Weather: Rain, fog, and other weather conditions can also obscure the sun.

* Sunrise and Sunset: Even on clear days, the sun is not directly overhead for the entire duration of daylight. Sunrise and sunset are times when the sun is low in the sky.

* Location: The amount of sunlight a place receives depends on its latitude and the time of year. For example, during winter, some areas may experience very short days with less direct sunlight.

So, while the sun is the source of daytime light, it's not always visible.