What gravitational effects happen during a total solar eclipse?
The first thing to realize is that the moon is in its ‘new’ phase, so whatever gravitational effects you might expect during a total solar eclipse also happen any time there is a New Moon, which happens every 28 days.
Starting as an observer on the ground, you are under the gravitational influence of Earth, the moon and the sun. At the time of the August 21, 2017 eclipse, Earth will be 151.4 million kilometers from the sun, and the moon will be located 365,649 km from the surface of Earth. Using Newton’s Law of Gravity, we can calculate the force of the sun, moon and Earth on an 80 kg person. Earth accounts for 784.1 Newtons of force (176.42 pounds), the moon provides 0.0029 Newtons (0.01 ounces) and the sun provides 0.4633 Newtons (1.6 ounces). But because our Earth rotates, this also provides an ‘anti-gravity’ centrifugal force we can also calculate. So if we add the forces with their correct directions we get a total gravitational force of 784.1 – 0.0029 – 0.4633 = 783.634 Newtons or 176.317 pounds. So, you will be about 1.7 ounces lighter!
The gravitational effect of the sun and moon being on the same side of Earth during New Moon is actually far more dramatic when you look at what happens to our entire planet. First, the gravitational ‘tidal’ force of the moon and sun cause a body tide in the solid rock of Earth. If you are on the same line defined by the centers of Earth, the sun and moon, Earth’s crust actually bulges upwards by about 40 millimeters across a thousand-kilometer area on Earth’s surface. So as you watch the total solar eclipse, feel free to imagine that you are standing on the ground 40 millimeters closer to the sun than it would be several hours later!