The changing appearance of the Moon during the lunar cycle is the result of the changing - relative positions of Earth, the Moon and the Sun.
Earth's shadow on the surface of the Moon.
amounts of light emitted by the Moon.
gravitational pull of the Moon as it orbits Earth.

relative positions of Earth, the Moon and the Sun.

Explanation:

A lunar eclipse is a phenomenon that occurs when the Earth comes between the Moon and the Sun thereby causing it to cover the Moon with its shadow.

Simply stated, lunar eclipse takes place when the Moon passes or moves through the Earth's shadow thereby blocking any ray of sunlight from reaching the Moon. Thus, the full moon appears deep red (blood moon).

Also, a lunar eclipse would occur only when the Sun, Earth, and Moon are closely aligned to form a straight line known as the syzygy.

There are three (3) types of lunar eclipse and these are;

1. Total lunar eclipse.

2. Partial lunar eclipse.

3. Penumbra lunar eclipse.

Hence, the changing appearance of the Moon during the lunar cycle is the result of the changing relative positions of Earth, the Moon and the Sun.