The part of the lunar cycle observed depends on how much of the ______________ side faces Earth.

The part of the lunar cycle observed depends on how much of the illuminated side faces Earth. The Moon reflects sunlight, and as it orbits around the Earth, the angle at which the Sun's light hits the Moon changes, leading to the various phases of the lunar cycle that we can observe from our planet. These phases include the New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter, and Waning Crescent. Each phase represents a different amount of the illuminated portion of the Moon that is visible from Earth.