Nautical Twilight When the centre of the Sun is between 6º and 12º below the horizon; the marine horizon becomes invisible.
Near-Earth Asteroid (NEA) An asteroid whose orbit brings it close to Earth's orbit.
Nautical Twilight -- For technical definition, please follow this link to the U.S. Naval Observatory Astronomical Applications website.
NE -- Near Encounter phase in flyby mission operations.
Nautical twilight: The time when the Sun is 6-12 degrees below the horizon. Sky begins to get noticeably bright.
nautical twilight: -6º and -12º
astronomical twilight: -12º and -18º
These values reflect the need for decreasing light levels for various activities.
nautical twilight (NASA SP-7, 1965) That period when the upper limb of the sun is below the visible horizon and the center of the sun is not more than 12 degrees below the celestial horizon. nautical year (NASA SP-7, 1965) = tropical year.
A Dictionary of Astronomy entry for nautical twilight
A Dictionary of Astronomy entry for civil twilight
A Dictionary of Astronomy entry for astronomical twilight
The Concise Oxford Dictionary of Music entry for Twilight of the Gods ...
Nautical twilight ends when the sun's center is 12° below the horizon; at about this time the light is too dim for the user of a sextant to see a sharp horizon.
Twilight - nautical Nautical twilight ends or begins when the Sun is 12° below the horizon.
Umbra Zone of maximum darkness in the shadow of a planet. Also the darkest part of a sunspot.
United States Government Printing Office. "Civil Twilight," "Nautical Twilight," and "Astronomical Twilight." Washington, DC: U. S. Government Printing Office, pp. A12 and A22-A45, 2000.
Those objects were 6 to 10 degrees over horizon at nautical twilight (5:06 am EST) - and I was still imaging M54, M2 and M75 past that time. Only M30 was left below horizon! So I am quite confident that imaging 109 M objects in a single is possible..
Civil twilight comprises the interval when the zenith distance, referred to the center of the Earth, of the central point of the Sun's disk is between 90°50' and 96°, nautical twilight comprises the interval from 96° to 102°, ...
horizon, and negative numbers indicate below the horizon --- with negative numbers usually being used in terms of how far below the horizon the sun is situated at a given time [for example, the boundary between civil twilight and nautical twilight is ...
 See also: Light, Twilight, Time, Atmosphere, Period
  
|
RSS
