nautical twilight
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nautical twilight
See twilight.Collins Dictionary of Astronomy © Market House Books Ltd, 2006
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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved
References in periodicals archive
The two bodies are, however, moving gradually closer together and by the end of September will be 'only' 32[degrees] apart with Saturn just 5[degrees] above the horizon at the start of
nautical twilight.
Greatest western elongation occurs on July 30 with Mercury just over 6[degrees] above the horizon at the start of
nautical twilight.
Nautical twilight ends when the Sun is 12[degrees] down; astronomical twilight ends when the Sun is 18[degrees] down.
On 2013 March 18 the comet will be 6[degrees] above the horizon at the start of
nautical twilight as seen from southern England.
How far from the center of a big city must you go at night to have your sky reach a darkness equivalent to that at the end of
nautical twilight, when the Sun is 12[degrees] below the horizon?
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