Final answer:
The highlands are brighter than the maria on the Moon because they are composed of different, more reflective rock types and have more craters. The maria are darker due to being made of basaltic material which absorbs more sunlight. The contrast in brightness is accentuated during the full Moon phase.
Step-by-step explanation:
The highlands and the maria on the Moon differ in brightness due to several factors. The most significant factor is that these areas are composed of different rock types. Highlands are the lighter, heavily cratered regions of the Moon, which are generally several kilometers higher than the maria. The highlands are older and have been bombarded by more impacts, creating a rough, reflective surface that makes them appear brighter.
Maria, on the other hand, are vast, dark basaltic plains on the Moon's surface formed by ancient volcanic eruptions. Since they are composed of different, darker materials such as basalt, they absorb more sunlight and thus appear darker. During the full phase of the Moon, the flat lighting accentuates the brightness contrasts between these regions. Highlighted by light streaks or rays known as ejecta, these contrasts are especially evident.
The highlands contain about ten times more craters than the maria, which suggests they are older; however, the number of craters alone does not determine the precise age of these regions. Geological activity, such as volcanic eruptions that form the maria, can resurface a moon, hiding old craters and making a region appear younger. Both the highlands and Maria provide insights into the Moon's history and geological processes.