We all hopefully know what gravity is by now and the age-old story of Newton and the apple tree, but what less of us may know is what causes shifts in gravity, how it changes even on Earth, and how things choose to reciprocate it.
While it is true that size is the defining factor of a celestial body’s personal field of gravity, distance is another important detail. After all, the sun is the center of our solar system, but not everything directly rotates it; moons go around planets while meteors unlucky enough to get too close to a planet end up on its surface. Even a single planet can experience subtly different gravity forces on different hemispheres provided its big enough because one side is closer to the sun. Given that everything in space is constantly in motion, there’s some pretty interesting phenomena out there.
Of course, gravity is also a two-way street. The moon pulls on Earth just as it pulls the moon, but the former’s lighter mass minimizes the effect so that it is only immediately apparent on fluids such as water, hence tides. Don’t think this is a moon-exclusive thing, either. The sun and even Venus can affect the tides as well, just nowhere near as much since they’re so far away.