A graduated line used to measure the speed of a vessel through the water or to measure the velocity of the current from a vessel at anchor. See current line. A tidal or tidal current constituent with a period that is independent of the rotation of the Earth but which depends upon the orbital movement of the Moon or the Earth. The principal lunar long period constituents have periods approximating the month and half month, and the principal solar long period constituents have periods approximating the year and half year. See tidal wave and tsunami.
Celestial longitude is measured in the ecliptic eastward from the vernal equinox.
The mean longitude of a celestial body moving in an orbit is the longitude that would be attained by a point moving uniformly in the circle of reference at the same average angular velocity as that of the body, with the initial position of the point so taken that its longitude would be the same as that of the body at a certain specified position in its orbit. With a common initial point, the mean longitude of a body will be the same in whatever circle it may be reckoned. A current paralleling the shore largely within the surf zone. It is caused by the excess water brought to the zone by the small net mass transport of wind waves. Long shore currents feed into rip currents.