tide

The general term tide refers to the rise and fall of sea level, attributed to the effect of the Moon's gravity, being near enough that the gravitational force on Earth is appreciably different on the regions of the Earth's surface nearer the Moon and further from the Moon. The term tide is also analogously used for the effects of the force of one body's gravity on another nearby body deforming its surface liquids as well as gases (atmosphere) and solids, the solid surface and within. The Earth experiences changes in the atmosphere (atmospheric tide) as well as the level of solid surface from these effects but they are not nearly as noticeable as that on the seas.

The apparent forces due to this difference in the pull of gravity at varying distances from the body that exerts the pull are termed tidal forces, which have a number of observable astronomical effects. These apparent forces can be expressed as a field, e.g., in terms of a potential (tidal potential, that may be symbolized by Φ_Tidal or in context, perhaps Φ_T) analogous to gravitational potential, but expressing the difference between the gravitational potential associated with the pair of bodies against that which one of the bodies would have if it were alone.