What phenomenon explains the frequent occurrence of lunar eclipses?

The phenomenon that explains the frequent occurrence of lunar eclipses is primarily associated with the alignment of the Earth, moon, and sun. A lunar eclipse occurs when the Earth directly obstructs sunlight from reaching the moon, causing the moon to pass into the Earth's shadow.

The option regarding the moon moving away from Earth does play a role in the overall dynamics of the Earth-moon system, but it does not directly contribute to the frequency of lunar eclipses. Lunar eclipses occur when the conditions aligning the sun, Earth, and moon are met, allowing for the moon to pass through the Earth's shadow.

The other choices, such as the moon being stationary relative to Earth, do not accurately describe the nature of the moon's orbit, as the moon is in constant motion. Similarly, while the eccentricity of the moon's orbit does have some influence over the distance between the moon and Earth during different phases, it is not the primary reason for lunar eclipses occurring. The moon's mass also does not play a direct role in the phenomenon of lunar eclipses; rather, it is the distances and alignments that are key.

Overall, the occurrence of lunar eclipses is effectively explained through the interaction of the orbits and the shadows cast, but the