Moon clouds. The illuminated area of the visible sphere (degree of illumination) is given by formula_3, where formula_4 is the elongation (i.e., the angle between Moon, the observer (on Earth) and the Sun). The gravitational attraction that masses have for one another decreases inversely with the square of the distance of those masses from each other. As a result, the slightly greater attraction that the Moon has for the side of Earth closest to the Moon, as compared to the part of the Earth opposite the Moon, results in tidal forces. Tidal forces affect both the Earth's crust and oceans. The
Discourse on the Tides is the motion of water relative to the earth, but annual revolution is the motion of the earth, and its water, relative to the sun. Annual revolution results in a force that accelerates the earth-water system but does not accelerate the water relative to the earth, in the same way that an observer standing on Earth's surface does not feel the gravitational attraction of the sun because the observer and Earth are moving together around the sun. The discourse does not include gravitational forces in its theory to explain the Earth's orbit and does not consider the relation between the