Get help from Pros. Remove ads. Promote your CV or LinkedIn profile.
The period from Nautical Twilight to the moment when the sun's centre is 18o below the horizon in the evening, and from the moment when the sun's centre is 18o below the horizon in the morning to the beginning of Nautical Twilight in the morning.

Related Terms

HORIZON SYSTEM OF COORDINATES

A set of celestial coordinates based on the celestial horizon as the primary great circle; usually altitude and azimuth or azimuth angle.

DOGWATCH

A short, evening period of watch duty on a ship

ANTI-OXIDANT

Additive that prolongs the induction period of a base oil in the presence of oxidizing conditions and catalyst metals at elevated temperatures. The additive is consumed and degradation products increase not only with increasing and sustained temperature, but also with increases in mechanical agitation or turbulence and contamination: air, water, metallic particles, and dust.

HORIZON

The great circle of the celestial sphere midway between the zenith and nadir, or a line resembling or approximating such a circle. The line where earth and sky appear to meet, and the projection of this line upon the celestial sphere, is called the visible or apparent horizon. A line resembling the visible horizon but above or below it is called a false horizon. The circle of the celestial sphere-formed by the intersection of the celestial sphere and a plane perpendicular to the zenith-nadir line is called sensible horizon if the plane is through any point, such as the eye of an observer; geoidal horizon if through any sea-level point; and celestial or rational horizon if through the center of the earth. The geometrical horizon was originally considered identi- cal with the celestial horizon, but the expression is now more commonly used to refer to the intersection of the celestial

HEAT WAVE

Unseasonably high temperatures extending over a period of a day or longer, particularly during the warm season of the year.

ICE BUOY

A sturdy buoy, usually a metal spar, used to replace a more easily damaged buoy during a period when heavy ice is anticipated.

HORIZON MIRROR

The mirror part of the horizon glass. The expression is sometimes used somewhat loosely to refer to the horizon glass.

MONSOON DRIFT

A drift current of the northeast Indian Ocean located north of the Indian Equatorial Countercurrent and south of the Bay of Bengal. During February and March when the northeast monsoon decreases in intensity, the monsoon drift is formed from the outflow of the Strait of Malacca and a small amount of north- westward flow along the upper southwest coast of Sumatra. Off the southwest coast of Sumatra, a current generally sets southeast during all months. It is strongest during October through April. The monsoon drift broadens as it flows westward and divides off the east coast of Sri Lanka, part joining the circulation of the Bay of Bengal and part joining the flow from the Arabian Sea. During April, the transition period between monsoons, the monsoon drift is ill-defined. A counterclockwise circulation exists between Sumatra and Sri Lanka. During May through October, the monsoon drift flows east to southeast. During November and December part of the monsoon drift is deflected into the Bay of Bengal and the remainder turns clockwise and flows southeastward.

HORIZON GLASS

The glass of a marine sextant, attached to the frame, through which the horizon is observed. The half of this glass nearer the frame is silvered to form the HORIZON MIRROR for reflecting the image of a celestial body; the other half is clear.

ICE ISLAND

A large piece of floating ice showing about 5 meters above the sea surface, which has broken away from an ice shelf, having a thickness of 30 to 50 meters and an area of from a few thousand square meters to l50 square nautical miles or more; usually characterized by a regularly undulating surface which gives it a ribbed appearance from the air.
Get help from Pros. Remove ads. Promote your CV or LinkedIn profile.

Related questions

MarineProHelp 2018 - 2022