Navigational lights placed in transit to mark an entry channel.

Related Terms

GREENWICH INTERVAL

An interval based on the moon's transit of the Greenwich celestial meridian, as distinguished from a local interval based on the moon's transit of the local celestial meridian.

HARBOR OF REFUGE

A place where ships in transit can find shelter from a storm. These are often man-made jetty enclosed areas along a featureless coastline where no nearby natural deep water harbors exist.

BEAR DOWN

Turn away from the wind, often with reference to a transit.

LIGHTS IN LINE

Two or more lights so situated that when observed in transit they define the alignment of a submarine cable, the limit of an area, an alignment for use in anchoring, etc. Not to be confused with RANGE LIGHTS which mark a direction to be followed.

WHARF

The place where ships tie up to unload and load cargo. A wharf typically has front and rear loading docks (aprons), a transit shed, open (unshedded) storage areas, truck bays, and rail tracks.

LOWER TRANSIT

Transit of the lower branch of the celestial meridian. Transit of the upper branch is called UPPER TRANSIT.

NAVY NAVIGATION SATELLITE SYSTEM

A satellite navigation system of the United States conceived and developed by the Applied Physics Laboratory of the Johns Hopkins University. It is an all-weather, worldwide, and passive system which provides two-dimensional positioning from low-altitude satellites in near-polar orbits. The Transit launch program ended in 1988, and the system is scheduled for termination in 1996, replaced by GPS.

LUNAR INTERVAL

The difference in time between the transit of the moon over the Greenwich meridian and a local meridian. The lunar interval equals the difference between the Greenwich and local intervals of a tide or current phase.

LUNICURRENT INTERNAL

The interval between the moon’s transit (upper or lower) over the local or Greenwich meridian and a specified phase of the tidal current following the transit. Examples are strength of flood interval and strength of ebb interval, which may be abbreviated to flood interval and ebb interval, respectively. The interval is described as local or Greenwich according to whether the reference is to the moon’s transit over the local or Greenwich meridian. When not otherwise specified, the reference is assumed to be local.

LUNITIDAL INTERVAL

The interval between the moon’s transit (upper or lower) over the local or Greenwich meridian and the following high or low water. The average of all high water intervals for all phases of the moon is known as mean high water lunitidal interval and is abbreviated to high water interval. Similarly the mean low water lunitidal interval is abbreviated to low water interval. The interval is described as local or Greenwich according to whether the reference is to the transit over the local or Greenwich meridian. When not otherwise specified, the reference is assumed to be local. When there is considerable diurnal inequality in the tide separate intervals may be obtained for the higher high waters, the lower high waters, the higher low waters and the lower low waters. These are designated respectively as higher high water interval, lower high water interval higher low water interval, and lower low water interval. In such cases, and also when the tide is diurnal, it is necessary to distinguish between the upper and lower transit of the moon with ref- erence to its declination.

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