TRUE DIRECTION

Horizontal direction expressed as angular distance from true north.

true_direction direction distance horizontal angular angular_distance

Related Terms

MOMENT OF INERTIA

The quantity obtained by multiplying the mass of each small part of a body by the square of its distance from an axis, and adding all the results.

moment_of_inertia distance mass square

Angular distance west of the Greenwich celestial meridian; the arc of the celestial equator, or the angle at the celestial pole, between the upper branch of the Greenwich celestial meridian and the hour circle of a point on the celestial sphere, measured westward from the Greenwich celestial meridian throug

greenwich_hour_angle distance circle angle angular angular_distance arc branch celestial celestial_meridian hour_circle west

HARPOON LOG

A log which consists of a rotator and distance registering device combined in a single unit, which is towed through the water. The TAFFRAIL LOG is similar except that the registering device is located at the taffrail, with only the rotator in the water.

harpoon_log device distance log registering taffrail taffrail_log

SHEAR RATE

The difference between the velocities along the parallel faces of a fluid element divided by the distance between the faces.

shear_rate fluid difference distance element parallel

HEIGHT OF TIDE

Vertical distance from the chart sounding datum to the water surface at any stage of the tide. It is positive if the water level is higher than the chart sounding datum. The vertical distance from the chart sounding datum to a high water datum is called RISE OF TIDE.

height_of_tide water surface chart water_level distance level datum rise vertical chart_sounding_datum high high_water stage

HOUR ANGLE

Angular distance west of a celestial meridian or hour circle; the arc of the celestial equator, or the angle at the celestial pole, between the upper branch of a celestial meridian or hour circle and the hour circl

hour_angle distance circle angle angular angular_distance arc branch celestial celestial_meridian hour_circle meridian west

INDIRECT ECHO

A radar echo which is caused by the electromagnetic energy being transmitted to the target by an indirect path and returned as an echo along the same path. An indirect echo may appear on the radar display when the main lobe of the radar beam is reflected off part of the structure of the ship (the stack for example) from which it is reflected to the target. Returning to own ship by the same indirect path, the echo appears on the PPI at the bearing of the reflecting surface. Assuming that the additional distance by the indirect path is negligible, the indirect echo appears on the PPI at the same range as the direct echo received. Also called FALSE ECHO.

indirect_echo bearing beam radar energy distance ship structure range stack target display echo electromagnetic_energy lobe

INITIAL GREAT CIRCLE COURSE

The direction, at the point of departure, of the great circle through that point and the destination, expressed as the angular distance from a reference direction, usually north, to that part of the great circle extending toward the designation. Also called INITIAL GREAT CIRCLE DIRECTION. See also FINAL GREAT CIRCLE COURSE.

initial_great_circle_course distance circle angular angular_distance great_circle reference

INFINITY

Beyond finite limits. In navigation, a source of light is regarded as at infinity if it is at such a great distance that rays from it can be considered parallel. The sun, planets, and stars can be considered at infinity without serious error.

infinity light distance

HYPERBOLA

An open curve with two parts, all points of which have a constant difference in distance from two fixed points called FOCI.

hyperbola difference distance constant curve fixed open