Dawn vs Sunrise

[Crunchy]

Does anyone know the time differences between Astronomical Dawn (sun 18 degrees below the horizon), Nautical Dawn (sun 12 degrees below the horizon) and the time given as Sunrise (the sun itself first seen on the horizon) at latitude 40 degrees north (Gelibolu)? Sunrise on 25th April 1915 was 0524 and on 7th August 1915 was at 0517. I am trying to work out when dawn actually occurred on both of these dates.

Regards

Chris

[salesie]

Does anyone know the time differences between Astronomical Dawn (sun 18 degrees below the horizon), Nautical Dawn (sun 12 degrees below the horizon) and the time given as Sunrise (the sun itself first seen on the horizon) at latitude 40 degrees north (Gelibolu)? Sunrise on 25th April 1915 was 0524 and on 7th August 1915 was at 0517. I am trying to work out when dawn actually occurred on both of these dates.

Regards

Chris

I believe the sun moves at a rate of 15 degrees per hour, Chris.

Cheers-salesie.

[Crunchy]

Thank you Salesie.

That makes it one degree every four minutes, although I understand that the difference in time between Dawn and Sunrise differs with the Latitude, very short at the tropics and much longer in the northern latitudes.

Regards

Chris

[Chris Henschke]

Chris,

I use this site.

http://aa.usno.navy.mil/cgi-bin/aa_pap.pl

Sun and Moon Data for One Day

The following information is provided for %28no Name Given) (longitude E26.3, latitude N40.2):

Sunday

25 April 1915 Universal Time + 2h

SUN

Begin civil twilight 04:55

Sunrise 05:24

Sun transit 12:13

Sunset 19:03

End civil twilight 19:31

MOON

Moonrise 13:12 on preceding day

Moonset 02:57

Moonrise 14:21

Moon transit 20:57

Moonset 03:21 on following day

Phase of the Moon on 25 April: waxing gibbous with 77% of the Moon's visible disk illuminated.

First quarter Moon on 22 April 1915 at 17:38 (Universal Time + 2h).

cheers,

Chris Henschke

[Crunchy]

Chris,

Thank you, that is fantastic. The Meteorological Bureau couldn't help, hence the request. I have just tracked down someone in GeoScience who has been a great help too.

Cheers

Chris

[Pete1052]

NOAA's National Weather Service Weather Forecast Office

Louisville, KY

Three Types of Twilight

We’re all familiar with the term twilight, that period of time just before sunrise or just after sunset. Did you know that there are actually three different twilight definitions?

Civil Twilight: the time at which the sun is 6 degrees below the horizon. At this time, there is enough light for objects to be clearly distinguishable and that outdoor activities can commence (dawn) or end (dusk) without artificial illumination. Civil twilight is the definition of twilight most widely used by the general public.

Nautical Twilight: the time when the center of the sun is 12 degrees below the horizon, and only general or vague outlines of objects are visible. During the evening this is when it becomes too difficult to perceive the horizon, and in the morning this is the point when the horizon becomes distinguishable. This term goes back to the days when sailing ships navigated by using the stars.

Astronomical Twilight: the time at which the sun is 18 degrees below the horizon. It is that point in time at which the sun starts lightening the sky. Prior to this time during the morning, the sky is completely dark. During the evening, this is the point where the sky completely turns dark.

So you can see the sequence, here are the times for these twilights at Louisville on January 8, 2006:

Start of Morning Astronomical Twilight: 6:26 AM EST

Start of Morning Nautical Twilight: 6:58 AM EST

Start of Morning Civil Twilight: 7:31 AM EST

Sunrise: 8:00 AM EST

Sunset: 5:40 PM EST

End of Evening Civil Twilight: 6:09 PM EST

End of Evening Nautical Twilight: 6:42 PM EST

End of Evening Astronomical Twilight: 7:14 PM EST

These data were provided from the U.S. Naval Observatory. You can get twilight information for other locations at their website.

*****

During operations in the field the U.S. Army uses the term Before Morning Nautical Twilight, which is the morning version of Nautical Twilight.

[Crunchy]

Thank you Pete. Much appreciated.

Regards

Chris

[Muerrisch]

Of course there is always the Arab simple definition:

dawn is when one can distinguish between a white and a black thread held in the palm of the hand.

Try it, very early one morning. Very!

[Guest geoff501]

Might not be exactly what you want but may be interesting. If you google for Geoclock, you will find a downloadable application that shows the sun moving over various earth maps at sunrise/sunset. You can set the time to any year and hour and point of interest and have it run 'real time' or various faster animation speeds. The free version only has one map of europe, but covers Turkey.

[Crunchy]

Many thanks Geoff. Much appreciated.

Cheers

Chris

[green_acorn]

Chris,

I used to use a very good descrition of BMAT, BMNT, First Light, BMCT and Dawn, along with sun and moon angles and lattitude, to publish light data daily, I no longer have the reference, but am chasing.

It described the phases as something along the lines of, from BMAT to BMNT, visual coordination of small groups can occur, hand signal directions can be given to vehicle drivers and pilots, topographic features become discernable at a distance. BMNT to First Light, coordination of larger groups and vehicle groups can safely occur, colours and topographic features can be recognised at a distance.

cheers,

Chris H