How does the Sun disturb the Moon’s motion around Earth?

In celestial mechanics, the Sun acts as a significant source of perturbation on the Moon’s orbit around Earth. Because the Moon is not always at the same distance from the Sun as Earth is, the Sun exerts a differential gravitational acceleration on the Moon, which disturbs its motion.12

Key effects of this solar influence include:

• Regression of the Lunar Nodes: The Sun is the primary cause of the regression of the Moon's ascending node. Because the Sun’s gravitational pull tends to draw the Moon toward the ecliptic plane, the line of nodes regresses, completing a full revolution every 18.61 years.2
• Secular and Periodic Perturbations: The Sun causes a secular increase in the longitude of the lunar perigee, completing a revolution every 8.85 years. Additionally, it induces periodic variations in the Moon's orbital inclination, eccentricity, and mean motion.2
• Evection: This specific term refers to the perturbation of the Moon's motion in its orbit caused by the Sun's gravitational attraction.3

While these disturbances are significant, the Moon remains in orbit because Earth's gravitational acceleration of the Moon is much stronger than the differential acceleration caused by the Sun.2