nautical twilight


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nautical twilight

See twilight.

nautical twilight

[′nȯd·ə·kəl ′twī‚līt]
(astronomy)
The interval of incomplete darkness between sunrise or sunset and the time at which the center of the sun's disk is 12° below the celestial horizon.

nautical twilight

nautical twilight
That period before sunrise and after sunset when the upper limb of the sun is below the visible horizon and the center of the sun is not more than 12° below the celestial or sensible horizon. During this interval of incomplete darkness, the degree of illumination is such that general outlines are still discernible, although detailed operations become impossible. All the bright stars are visible at this time. It is the time when the navigational stars are visible and the sea horizon is still sufficiently visible to permit celestial observations with a sextant.
References in periodicals archive ?
Saturn is edging gradually into the twilight and will be difficult to spot low down in the west-southwest at the beginning of October, when it will be only 5[degrees] in altitude at the start of nautical twilight.
Nautical Twilight is when the Sun is between six and 12 degrees below the horizon.
We assume he means that as Odysseus set sail shortly after sunset, at nautical twilight the Pleiades and Bootes were simultaneously visible, and that Bootes would be the later-setting of the two", Magnasco explained.