The monthly tidal cycle is days because that’s how long it takes the Moon to complete an orbit around Earth. During its orbit around Earth, the Moon’s changing position influences tidal conditions on Earth.
The Monthly Tidal Cycle During the monthly tidal cycle, the phase of the Moon changes dramatically. When the Moon is between Earth and the Sun, it cannot be seen at night, and it is called the new moon.
When the Moon is on the side of Earth opposite the Sun, its entire disk is brightly visible, and it is called a full moon. A quarter moon—a moon that is half lit and half dark as viewed from Earth—occurs when the Moon is at right angles to the Sun relative to Earth.