When the moon is directly overhead, a person's weight decreases: Why?

When the Moon is directly overhead, a person’s weight experiences a slight decrease due to the gravitational pull exerted by the Moon. This phenomenon, while subtle, is a fascinating example of how gravitational forces affect weight on Earth.

To understand why this happens, it’s essential to differentiate between weight and mass. Mass is the amount of matter an object has and doesn’t change regardless of location. Weight, however, is the force of gravity acting on that mass. Because gravitational forces can vary slightly depending on nearby massive objects, weight is subject to minor fluctuations.

The gravitational force the Moon exerts on an object on Earth is weaker than Earth’s gravitational force, but it is still significant enough to produce a measurable effect. Gravity follows the inverse-square law, meaning its strength decreases with the square of the distance from the source. The Earth’s gravitational pull is far stronger than the Moon’s because Earth is much more massive and much closer to us. However, when the Moon is directly overhead, its gravitational pull adds an upward force on a person or object. This causes a slight reduction in the net downward force exerted by Earth’s gravity, resulting in a minor decrease in weight.

However, this difference is too small
This reduction in weight is small because the gravitational influence of the Moon on Earth is weak compared to Earth’s own gravity. The Moon’s gravitational pull at Earth’s surface is about 1/300,000th of Earth’s gravitational force. Still, this force is enough to create noticeable phenomena, like the ocean tides, where the Moon’s gravity pulls on Earth’s waters, creating high and low tides.


"The effect of the Sun's pull (and that of the Moon, slightly stronger) is complicated, because the Earth on which you stand is also pulled. In any case, the pull is too small to observe (the effect of the Earth's rotation is also small but much bigger," NASA explains in a post.

How less is the difference?
When the Moon is overhead, the gravitational pull towards it reduces the effective gravitational force that pulls you towards Earth's center. This results in an apparent loss of weight temporarily by a minuscule margin; this has been computed by scientists to be some 0.48 milligrams per kilogram of body weight. For an individual weighing 70 kilograms this translates into a loss of about 0.034 grams.