Science / Tides and Currents Glossary

Angular Velocity Of The Earths Rotation: Time rate of change of angular displacement relative to the fixed stars. It is equal to 0.729,211 x 10-4 radian/second.

Annual Inequality: Seasonal variation in water level or current, more or less periodic, due chiefly to me teorological causes.

Anomalistic: Pertaining to the periodic return of the Moon to its perigee or the Earth to its perihelion. The anomalistic month is the average period of the revolution of the Moon around the Earth with r . . . View Full Definition

Anomaly: As applied to astronomy, the anomaly is the angle made at any time by the radius vector of a planet or moon with its line of apsides, the angle being reckoned from perihelion or perigee in t . . . View Full Definition

Antarctic Circumpolar Current: The largest permanent current in the world, setting eastward around the Antarctic Continent south of Cape Horn, Cape of Good Hope, Tasmania, and New Zealand. Through Drake Passage, it transp . . . View Full Definition

Anticyclonic Ring: A meander breaking off from the main oceanic current and spinning in a clockwise direction in the northern hemisphere (counter-clockwise in southern).

Antilles Current: A North Atlantic Ocean current setting northwestward along the northeast coasts of the Bahama Islands.

Aphelion: The point in the orbit of the Earth (or other planet, etc.) Farthest from the Sun.

Apogean Tides Or Tidal Currents: Tides of decreased range or currents of decreased speed occurring monthly as the result of the Moon being in apogee. The apogean range (An) of the tide is the average range occurring at the . . . View Full Definition

Apogee: The point in the orbit of the Moon or a man-made satellite farthest from the Earth. The point in the orbit of a satellite farthest from its companion body.

Apparent Secular Trend: The non-periodic tendency of sea level to rise, fall, or remain stationary with time. Technically, it is frequently defined as the slope of a least-squares line of regression through a relat . . . View Full Definition

Apparent Time: Time based upon the true position of the Sun as distinguished from mean time, which is measured by a fictitious Sun moving at a uniform rate. Apparent time is that shown by the sundial, and . . . View Full Definition

Apsides: The points in the orbit of a planet or moon which are the nearest and farthest from the center of attraction. In the Earth's orbit these are called perihelion and aphelion, and in the Moon's . . . View Full Definition

Astres Fitifs: Fictitious celestial bodies which are assumed to move in the celestial equator at uniform rates corresponding to the speeds of the several harmonic constituents of the tide producing force. . . . View Full Definition

Astronomical Time: Time formerly used in astronomical calculations in which the day began at noon rather than midnight. The astronomical day commenced at noon of the civil day of the same date. The hours of th . . . View Full Definition

Augmenting Factor: A factor, used in connection with the harmonic analysis of tides or tidal currents by stencils, to allow for the fact that the tabulated hourly heights or speeds used in the summation for an . . . View Full Definition

Automatic Tide Gauge: An instrument that automatically registers the rise and fall of the water level. In some instruments, the registration is accomplished by recording the heights at regular time intervals in d . . . View Full Definition

Azimuth: Azimuth of a body is the arc of the horizon intercepted between the north or south point and the foot of the vertical circle passing through the body. It is reckoned in degrees from either t . . . View Full Definition

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