Answer:
The light part of the Moon appeared to get smaller over time because of the change in the relative position of the Moon, the Sun, and the Earth. This is known as the lunar phase. The changing appearance of the Moon from the Earth's perspective is caused by the Moon's orbit around the Earth and the position of the Moon and Sun relative to the Earth. The Moon's phases are caused by the angle between the Moon, Earth, and Sun changing, as the Moon orbits the Earth. When the Moon is between the Earth and the Sun, the side facing the Earth is not illuminated by sunlight, so it appears dark, and this is called a new moon. When the Moon is on the opposite side of the Earth from the Sun, the entire side of the Moon facing the Earth is illuminated by sunlight, so it appears full, and this is called a full moon. As the Moon moves in its orbit, the angle between the Sun, Earth, and Moon changes, causing the illuminated portion of the Moon visible from the Earth to change, leading to different lunar phases.