The shadow of an object moves as the sun's position changes throughout the day. This movement is a direct result of the sun's trajectory across the sky, which is influenced by the Earth's rotation and tilt. As the sun moves from east to west, the angle of sunlight changes, causing the shadow to shift accordingly.

The shadow's movement is most pronounced during the morning and afternoon when the sun is lower in the sky. At noon, when the sun is directly overhead, the shadow is shortest and moves very little. This is because the sun's rays are perpendicular to the ground, minimizing the angle of incidence and, consequently, the length of the shadow.

The rate at which the shadow moves is also affected by the time of year. During the summer months, when the sun is higher in the sky, shadows are shorter and move more slowly. In contrast, during the winter months, when the sun is lower, shadows are longer and move more quickly.

Data from solar position calculations and shadow length measurements support this phenomenon. For instance, a study by the U.S. National Renewable Energy Laboratory (NREL) found that the shadow length of a 1-meter object varies from approximately 0.5 meters at noon to over 5 meters at sunrise or sunset. This variation is due to the sun's changing angle of incidence throughout the day.

In conclusion, the shadow moves with direct sunlight due to the sun's changing position in the sky, which is influenced by the Earth's rotation and tilt. The movement of the shadow is most pronounced during the morning and afternoon, and it varies with the time of year, with shorter shadows and slower movement in the summer and longer shadows and faster movement in the winter.