**Science / Tides and Currents / Parallax:** In tidal work, the term refers to horizontal parallax, which is the angle formed at the center of a celestial body between a line to the center of the Earth and a line tangent to the Earth's surface. Since the sine of a small angle is approximately equal to the angle itself in radians, it is usually taken in tidal work simply as the ratio of the mean radius of the Earth to the distance of the tide-producing body. Since the parallax is a function of the distance of a celestial body, the term is applied to tidal inequalities arising from the changing distance of the tide-producing body.

Science / Tides and Currents / Parallax Inequality: The variation in the range of tide or in the speed of a tidal current due to changes in the distance of the Moon from the Earth. The range of tide and speed of the current tend alternately to increase MORE

Science / Tides and Currents / Age Of Parallax Inequality: The time interval be tween perigee of the Moon and the maximum effect of parallax upon range of tide or speed of the tidal current. This age may be computed from the harmonic constants by the formula: MORE

Science / Tides and Currents / Parallax Reduction: A processing of observed high and low waters to obtain quantities depending upon changes in the distance of the Moon, such as perigean and apogean ranges. MORE