Answer:
the rotation of the globe
Step-by-step explanation:
As mentioned the model is representing the day and night cycle of earth thus the lamp must be the sun and the globe is earth.
The earth completes one year in taking one complete revolution around the sun (globe revolve around lamp).Thus due to revolution of earth the year gets completed.
The day and night of earth is due to rotation of earth on its own axis. The earth took 24 hours to complete one rotation on its axis.
Thus the rotation of globe causes it to receive light at different times.