Hours of darkness

TMO · Post by **TMO** » Fri Oct 10, 2003 12:28 am

Now that we here in the UK are entering Autumn and the nights are drawing in, something that has been puzzling me for some time springs to mind - why are the nights so short in AA:RDOA? Sunrise is at 04-00 (IMO too early) and sunset at 21-00 (IMO too late). I checked out a website (http://mach.usno.navy.mil/cgi-bin/aa_pap) and came across the following:

U.S. Naval Observatory
Astronomical Applications Department

The following information is provided for Arnhem (longitude E5.2, latitude N52.6):

Sunday
17 September 1944 Universal Time + 1h

SUN
Begin civil twilight 05:42
Sunrise 06:17
Sun transit 12:34
Sunset 18:51
End civil twilight 19:25

If these times are right then sunrise should be around 06-00 and sunset around 19-00, giving 4 extra hours of night time compared to that currently modelled. Surely these 'extra' hours of darkness must be a major influence on combat tactics. Any thoughts?

Tim

Fallschirmjager · Post by **Fallschirmjager** » Fri Oct 10, 2003 4:14 am

I have wondered while nights were so short myself

Sarge · Post by **Sarge** » Fri Oct 10, 2003 5:23 am

TMO wrote:Now that we here in the UK are entering Autumn and the nights are drawing in, something that has been puzzling me for some time springs to mind - why are the nights so short in AA:RDOA? Sunrise is at 04-00 (IMO too early) and sunset at 21-00 (IMO too late). I checked out a website (http://mach.usno.navy.mil/cgi-bin/aa_pap) and came across the following:

U.S. Naval Observatory
Astronomical Applications Department

The following information is provided for Arnhem (longitude E5.2, latitude N52.6):

Sunday
17 September 1944 Universal Time + 1h

SUN
Begin civil twilight 05:42
Sunrise 06:17
Sun transit 12:34
Sunset 18:51
End civil twilight 19:25

If these times are right then sunrise should be around 06-00 and sunset around 19-00, giving 4 extra hours of night time compared to that currently modelled. Surely these 'extra' hours of darkness must be a major influence on combat tactics. Any thoughts?

Tim

Nice point guy.............good eye

Arjuna · Post by **Arjuna** » Fri Oct 10, 2003 6:09 am

TMO wrote:Now that we here in the UK are entering Autumn and the nights are drawing in, something that has been puzzling me for some time springs to mind - why are the nights so short in AA:RDOA? Sunrise is at 04-00 (IMO too early) and sunset at 21-00 (IMO too late). I checked out a website (http://mach.usno.navy.mil/cgi-bin/aa_pap) and came across the following:

U.S. Naval Observatory
Astronomical Applications Department

The following information is provided for Arnhem (longitude E5.2, latitude N52.6):

Sunday
17 September 1944 Universal Time + 1h

SUN
Begin civil twilight 05:42
Sunrise 06:17
Sun transit 12:34
Sunset 18:51
End civil twilight 19:25

If these times are right then sunrise should be around 06-00 and sunset around 19-00, giving 4 extra hours of night time compared to that currently modelled. Surely these 'extra' hours of darkness must be a major influence on combat tactics. Any thoughts?

Tim

Tim,

Very interesting information. This data is at odds with the research we have done. I tried the link you provided, but cannot gain access.

TMO · Post by **TMO** » Fri Oct 10, 2003 1:29 pm

Arjuna

Try http://aa.usno.navy.mil/data/docs/RS_OneDay.html.

Tim

Arjuna · Post by **Arjuna** » Fri Oct 10, 2003 5:29 pm

Tim,

No, that doesn't work either. Military links often filter out requests from non-military sites.

JeF · Post by **JeF** » Fri Oct 10, 2003 10:47 pm

Tim,

Very good ! Two thumbs up mate !
Despite some of us being not far from the actual MG battlefield (myself included), this was not spotted before.

On the other hand :
- the game might be delayed due to this late finding

- won't we have a harder time getting to the bridge on day 1 with our paras ??

Night might fall to quickly.
- and finally, I've always found the night too long in game and waits anxiously for dawn (a bit before, in fact) to launch decisive attacks and long marches.

Troops are so ineffective at night.

Dave,

You might want to search google for "Complete Sun and Moon Data for One Day", that's the title of the page referred by Tim. I had no problem accessing it, BTW. You might find some copies of the site.
By looking at some links, I found this URL : http://www.ga.gov.au/nmd/geodesy/astro/sunrise.jsp. But I had a hard time identifying its location.

If all else fails, here is a link to astronomical ephemeris from the Jet Propulsion Laboratory : http://ssd.jpl.nasa.gov/cgi-bin/eph . Ask for Solar ephemeris hour by hour (or minutes by minutes), you'll be covered by numbers and information. One of the column indicate the Night/Day status.

Cheers,

JeF.

TMO · Post by **TMO** » Sat Oct 11, 2003 1:40 am

Dave

Just type in 'sunrise and sunset' into Google - the first hit should be the website you want (I'm not logging in from a military site).

Whatever you do, don't delay the launch of HTTR - you can always publish a patch or make changes in Game 3 (got to say, really looking forward to Normandy game (4?)). I love playing the game but want it to be as accurate as possible. Being able to ' have a go' myself adds a whole new dimension to understanding these historic events.

Tim

Arjuna · Post by **Arjuna** » Sat Oct 11, 2003 4:12 am

Tim/JeF,

Thanks for the leads. I could not get the link to the http://aa.usno.navy.mil/data/docs/RS_OneDay.html. no matter which path I went through. But I went to the Australian site that JeF mentioned http://www.ga.gov.au/nmd/geodesy/astro/sunrise.jsp and using the maparama site got the Lat and Long for Arnhem and then got a print out. Here it is:

Arnhem Lat= 51°59'00" Long= +5°54'00"
TIMES OF SUNRISE AND SUNSET
(for ideal horizon & meteorological conditions)
Time zone: +1.00 hours
17/09/1944 Rise 0614 Set 1848

TIMES OF CIVIL TWILIGHT
(for ideal horizon & meteorological conditions)
Time zone: +1.00 hours
17/09/1944 Rise 0540 Set 1922

TIMES OF NAUTICAL TWILIGHT
(for ideal horizon & meteorological conditions)
Time zone: +1.00 hours
17/09/1944 Rise 0500 Set 2002

TIMES OF ASTRONOMICAL TWILIGHT
(for ideal horizon & meteorological conditions)
Time zone: +1.00 hours
17/09/1944 Rise 0417 Set 2045

TIME OF SUN TRANSIT
(for ideal horizon & meteorological conditions)
Time zone: +1.00 hours
17/09/1944 Transit time 1231

Computed using National Mapping Division's sunrisenset program, version 2.2

Also here is a definition of the terms used:

According to the U.S. Naval Observatory, civil twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 6 degrees below the horizon. This is the limit at which twilight illumination is sufficient, under good weather conditions, for terrestrial objects to be clearly distinguished; at the beginning of morning civil twilight, or end of evening civil twilight, the horizon is clearly defined and the brightest stars are visible under good atmospheric conditions in the absence of moonlight or other illumination. In the morning before the beginning of civil twilight and in the evening after the end of civil twilight, artificial illumination is normally required to carry on ordinary outdoor activities. Complete darkness, however, ends sometime prior to the beginning of morning civil twilight and begins sometime after the end of evening civil twilight.

Sunrise and sunset conventionally refer to the times when the upper edge of the disk of the Sun is on the horizon, considered unobstructed relative to the location of interest. Atmospheric conditions are assumed to be average, and the location is in a level region on the Earth's surface.

Astronomical Twilight
When the position of the Sun is below the horizon and between 12 and 18 degrees below the horizon.

We would use "nautical twilight" not "civil twilight" as the basis for determining dawn and dusk. So according to these figures "first light" would be 0500 and last light would be 2000. As you point out this would lengthen each night by two hours.

This is rather strange though and at odds with first hand reports of the Guards armoured division securing their first dayas objective at 2100 in the fading twilight and with other reports from Arnhem.

This needs more research to resolve. As you suggest we'll press on with the release and if necessary put out a patch.

Thanks very much for this info. Well done,

Dave

JJKettunen · Post by **JJKettunen** » Sat Oct 11, 2003 5:43 am

Arjuna wrote: We would use "nautical twilight" not "civil twilight" as the basis for determining dawn and dusk. So according to these figures "first light" would be 0500 and last light would be 2000. As you point out this would lengthen each night by two hours.

I found the above sites when searching for light condition info for my scenarios (guess for what game?...lol). AFAIK, civil twilight should be used because it's the actual dawn and dusk as we experience it (and that's why it's called "civil").

Arjuna · Post by **Arjuna** » Sat Oct 11, 2003 6:55 am

No disagree. First light commences with nautical twilight. Dawn attacks are put in at first light so the assault troops can get as close to the objective without being seen. Therefore, if you are defending, your front line soldiers would stand to just prior to first light, which commences with nautical twilight. From my own personal experience we always stood to at least an hour before sunrise.

Sarge · Post by **Sarge** » Sat Oct 11, 2003 8:54 am

Arjuna wrote:No disagree. First light commences with nautical twilight. Dawn attacks are put in at first light so the assault troops can get as close to the objective without being seen. Therefore, if you are defending, your front line soldiers would stand to just prior to first light, which commences with nautical twilight. From my own personal experience we always stood to at least an hour before sunrise.

From my pesonal experience I cant back that up. But I would like to emphasize at LEAST an hour before sunrise

jamespcrowley · Post by **jamespcrowley** » Sat Oct 11, 2003 1:11 pm

Not sure if this is of any use.

Irish Guards History gives the following:

For Sunday 17 Sept 1944, "sunset is at 18.47 and last light at 19.41"

1/Dorset's battalion history have an entry: at 21.00 " it is now raining and pitch black"

JJKettunen · Post by **JJKettunen** » Sat Oct 11, 2003 2:22 pm

Here are more definitions about twilight (from the first link above).

"Civil twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 6 degrees below the horizon. This is the limit at which twilight illumination is sufficient, under good weather conditions, for terrestrial objects to be clearly distinguished; at the beginning of morning civil twilight, or end of evening civil twilight, the horizon is clearly defined and the brightest stars are visible under good atmospheric conditions in the absence of moonlight or other illumination. In the morning before the beginning of civil twilight and in the evening after the end of civil twilight, artificial illumination is normally required to carry on ordinary outdoor activities. Complete darkness, however, ends sometime prior to the beginning of morning civil twilight and begins sometime after the end of evening civil twilight.

Nautical twilight is defined to begin in the morning, and to end in the evening, when the center of the sun is geometrically 12 degrees below the horizon. At the beginning or end of nautical twilight, under good atmospheric conditions and in the absence of other illumination, general outlines of ground objects may be distinguishable, but detailed outdoor operations are not possible, and the horizon is indistinct.

Astronomical twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 18 degrees below the horizon. Before the beginning of astronomical twilight in the morning and after the end of astronomical twilight in the evening the Sun does not contribute to sky illumination; for a considerable interval after the beginning of morning twilight and before the end of evening twilight, sky illumination is so faint that it is practically imperceptible."

TMO · Post by **TMO** » Sat Oct 11, 2003 6:33 pm

Dave

I presume at the moment day and night are currently modelled as either complete daylight or complete darkness. Is it possible to model twilight hours, i.e. a gradual progression to darkness or light?

Tim

jmeyer7000both · Post by **jmeyer7000both** » Sun Oct 12, 2003 7:48 am

Sorta curious as to what time everyone would have been using: local London or local Continental time, at least, for writing-up reports? Was everyone using GMT? Were the the AB forces in theatre set to + 1 hr from London?

Cheers,
Jim M.

Arjuna · Post by **Arjuna** » Mon Oct 13, 2003 2:54 am

Tim,

It's possible. I'll add it to the wish list.

Arjuna · Post by **Arjuna** » Mon Oct 13, 2003 2:55 am

Jim,

Good question. I'm not sure. Does anyone know?

CriticalMass · Post by **CriticalMass** » Mon Oct 13, 2003 12:18 pm

I seem to recall reading somewhere that this was a major bone of contention between the british and her ally (the americans).

It went something like:

British: be nice to the the locals; use the local time.
Americans: Be nice to us; use standard GMT

I maybe way off but I think thats what I read

Grouchy · Post by **Grouchy** » Mon Oct 13, 2003 6:29 pm

In WWII the germans also introced the summersaving times in Nederland, so there is another additional hour time difference.