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Statutory, required lights shown by vessels during the hours between sunset and sunrise, in accordance with international agreements.

Related Terms

LIGHT IRON

An iron bar mounted near the main shrouds which support the navigation lights

NAVAL VESSEL LIGHTS ACT

Authorized departure from the rules of the road for character and position of navigation lights for certain naval ships. Such modifications are published in Notice to Mariners.

RUNNING LIGHTS

Navigation lights used while under way and making way.

ANTITWILIGHT

The pink or purplish zone of illumination bordering the shadow of the earth in the dark part of the sky opposite the sun after sunset or before sunrise. Also called ANTI CREPUSCULAR ARCH.

DAYLIGHT CONTROL

A photoelectric device that automatically lights and extinguishes a navigation light, usually lighting it at or about sunset and extinguishing it at or about sunrise. Also called SUN RELAY, SUN SWITCH, SUN VALVE.

EVENING TWILIGHT

The period of time between sunset and darkness

GREEN FLASH

A brilliant green coloring of the upper edge of the sun as it appears at sunrise or disappears at sunset when there is a clear, distinct horizon. It is due to refraction by the atmosphere, which disperses the first (or last) spot of light into a spectrum and causes the colors to appear (or disappear) in the order of refrangibility. The green is bent more than red or yellow and hence is visible sooner at sunrise and later at sunset.

PURPLE LIGHT

The faint purple glow observed on clear days over a large region of the western sky after sunset and over the eastern sky before sunrise.

SUNSET

The crossing of the visible horizon by the upper limb of the setting sun.

TWILIGHT

The period of incomplete darkness following sunset (evening twilight) or preceding sunrise (morning twilight). Twilight is designated as civil, nautical, or astronomical, as the darker limit occurs when the center of the sun is 6°, 12°, or 18° below the celestial horizon, respectively.

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