What causes the gradual change in the length of your shadow over the course of the day?

The gradual change in the length of your shadow throughout the day is primarily caused by the position of the Sun in the sky. As the Sun rises in the morning, it casts longer shadows because it is lower on the horizon. As the Sun moves higher toward noon, shadows become shorter, and they lengthen again in the afternoon as the Sun sets. This change is a result of the angle at which sunlight strikes the ground.