National Museum of American History, Behring Center
 

 
Lighthouse Postcards

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 Glossary

Beacon
A signaling or guiding device, such as a lighthouse, located on a coast.
 
Caisson
A watertight structure within which construction work is carried on under water.
 
Day-marker (day-board)
A usually unlit shaped sign board mounted on a post or piling which indicates a channel centerline (see Range markers) or boundary: square green (or black) signs on the left (port) side of the channel when returning from open water, and triangular red signs on the right (starboard) side.
 
Decommission
To withdraw from active service.
 
Fog signal
A bell, horn, whistle or other device that sounds an alarm, often automatically, near places of danger where visible signals would be hidden in rainy or foggy weather.
 
Gable
The end wall of a building, as distinguished from the front or rear side.
 
Guyed mast
A pole or tower set upright which is steadied or secured with ropes or cable.
 
Jetty
A structure, such as a pier or rock fill, that projects into a body of water to influence the current or tide or to protect a harbor or shoreline from storms or erosion.
 
Latitude
The angular distance of a location on the earth’s surface (or on a chart or map), measured in degrees, minutes and seconds north or south of the equator along a meridian.
 
Light Characteristic
The color and pattern of light and dark which identify a particular lighthouse; these include:
 
Alternating
Alight showing different colors alternately [for example, an alternating green and white light would be noted on a chart as Al GW].
 
Eclipsed light
A fixed light which is interrupted briefly by darkness at a defined interval.
 
Fixed light
A steady, unblinking light [noted as F on a chart].
 
Flashing Light
A light in which the total duration of light in a period is shorter than the total duration of darkness and the appearances of light (flashes, noted as Fl on a chart) are usually of equal duration.
 
Group-flashing
A flashing light in which a group of flashes, specified in number [e.g., Fl (2) on a nautical chart], is regularly repeated.
Isophase A light in which all durations of light and darkness are equal, and abbreviated (Iso) on nautical charts.
 
Occulting
A light in which the total duration of light in a period is longer than the total duration of darkness and the intervals of darkness (eclipses) are usually of equal duration; abbreviated Oc on nautical charts.

Longitude
The angular distance of a location on the earths surface (or on a chart or map), measured in degrees, minutes and seconds, east or west of the prime (i.e., zero) meridian at Greenwich, England.
 
Meridian
A great circle on the earth’s surface passing through both the north and south poles.
 
Nautical mile
A distance equal to one minute of arc of a great circle (e.g., a meridian of latitude); hence one minute of latitude equals 1,852 meters or about 6076 feet (1.15 miles).
 
Pilings
A group of piles used for a structure; a pile is a heavy beam of timber, concrete, or steel, driven into the earth as a foundation or support for a structure.
 
Private aid to navigation
A buoy, light or other marker owned and maintained by any individual or organization other than the U.S. Coast Guard.
 
Range markers
Ranges are imaginary lines defined by pairs of aids to navigation. When the two lit and/or un-lit markers appear to be in line with each other, the mariner is maintaining a safe course within the channel. The appropriate nautical chart [see, for example, Hospital Point, MA chart (13267_hp_m_bi)] must be consulted when using ranges to determine whether the range marks the centerline of the navigable channel as well as what section of the range length may be safely used.
 
Red sector
An angular portion of the arc around a white light within which mariners would see a red light warning against proceeding toward the light within that arc; a warning that the vessel is not moving in a safe channel (e.g., see Browns Head, ME, chart).
 
Rubble stone
Irregular fragments or pieces of rock used in masonry construction.
 
Scale (Chart)
The ratio, printed on a chart, of the distance between any two points on the chart to the distance between the same two points on the earth's surface. E.g., 1 inch on a 1:80,000 scale chart represents 80,000 inches on the earth's surface (about 1.26 statute miles, or 1.10 nautical miles).
 
White sector
An angular portion of the arc around a red light within which mariners would see a white light warning against proceeding toward the light within that arc; a warning that the vessel is not moving in a safe channel.

 
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