Here's why:
* Lunar Phases are about Perspective: The phases of the moon (new moon, crescent, full moon, etc.) are simply how much of the sunlit side of the moon we see from Earth. The moon's shape and mass don't actually change.
* Gravity is a Function of Mass and Distance: The gravitational pull of the moon is determined by its mass and its distance from Earth. These factors remain constant.
However, there is a slight change in the *total* gravitational force on Earth during the lunar cycle due to the alignment of the Sun, Earth, and Moon:
* Spring Tides: When the Sun, Earth, and Moon are aligned (during new and full moons), their combined gravitational pull creates stronger tides called "spring tides." These tides are higher than usual.
* Neap Tides: When the Sun, Earth, and Moon form a right angle (during quarter moons), the gravitational pull is weaker, resulting in "neap tides" that are lower than average.
While these tides are influenced by the Moon's gravity, the moon's gravity itself doesn't change. It's just the combined effect of the Sun and Moon's gravity that varies depending on their alignment.
