Definitions of 'twilight'

[rbgarr]

From www.wunderground.com (http://www.wunderground.com)
Twilight This is the time before sunrise and after sunset where it is still light outside, but the sun is not in the sky.

Civil Twilight This is defined to be the time period when the sun is no more than 6 degrees below the horizon at either sunrise or sunset. The horizon should be clearly defined and the brightest stars should be visible under good atmospheric conditions (i.e. no moonlight, or other lights). One still should be able to carry on ordinary outdoor activities.

Nautical Twilight This is defined to be the time period when the sun is between 6 and 12 degrees below the horizon at either sunrise or sunset. The horizon is not defined and the outline of objects might be visible without artificial light. Ordinary outdoor activities are not possible at this time without extra illumination.

Astronomical Twilight This is defined to be the time period when the sun is between 12 and 18 degrees below the horizon at either sunrise or sunset. The sun does not contribute to the illumination of the sky before this time in the morning, or after this time in the evening. In the beginning of morning astronomical twilight and at the end of astronomical twilight in the evening, sky illumination is very faint, and might be undetectable.

[CarlZog]

Civil and Nautical are what matters.

I'll usually break out a sextant at Civil dusk; Nautical dawn. Planets, and some of the brightest stars will start to show up about then. But I'll precalculate the locations of the stars I expect to see at about half way between Civil and Nautical. Usually by Nautical (at pm, Civil am), the horizon is getting pretty dim; I find I can still shoot westerly, but my results get sketchier after that.

Was there a question that prompted you to post this?

Carl

[rbgarr]

Nope, just thought it might interest some readers... nothing more.

[Bruce Hooke]

Civil and Nautical are what matters.

Unless you are an astronomer! :D

[Bruce Hooke]

I love that time period during civil twilight in the morning when the eastern horizon is a bit lighter, light enough for things like trees to be in silhouette against it, but to the west the sky is still a rich black.

[John B]

Seeing that is something I aspire to. One day...

[rbgarr]

The whole family, grandparents to toddlers, were amazed and humbled by the sky one evening as we motored back from a day exploring Monhegan and Manana Islands.

When the sun set off the bow the sea fell to a glassy calm reflecting reds, oranges and yellows on the long swells. Overhead the sky was a dome of pale green and blue turning to mauve and a deeper purple. The full moon's disc broke the eastern horizon beyond the Islands off the stern and a wavering silver path followed us home on our wake.

[George Ray]

Thanks!
I had run run across 'Asto Twilight' recently and it was helpful to see a definition.

[P.I. Stazzer-Newt]

Friday
3 April 2009 Eastern Daylight Time

SUN
Begin civil twilight 5:42 a.m.
Sunrise 6:12 a.m.
Sun transit 12:38 p.m.
Sunset 7:06 p.m.
End civil twilight 7:35 p.m.

MOON
Moonrise 11:01 a.m. on preceding day
Moonset 3:05 a.m.
Moonrise 12:18 p.m.
Moon transit 8:06 p.m.
Moonset 3:39 a.m. on following day



http://aa.usno.navy.mil/data/docs/RS_OneDay.php

[Uncle Duke]

I was told that Bedouins, who need to know 'dawn' and 'dusk' precisely for prayer reasons, would hold up a white thread and a black thread morning and evening.
When you can tell the difference, in the morning, it was officially dawn.
When you cannot tell the different, in the evening, it was officially dusk.