Re: Terminator
hi Doug Try www.daylightmap.com/ as an alternative regards Ian Maddocks Chester, UK -- From: "Douglas Bateman" Sent: Wednesday, September 14, 2011 10:25 PM To: "Sundial" Subject: Terminator Does anyone know of a link or an "app" that shows the terminator in graphic form over the world. I used to use a 'mapmaker' website but that seems to have disappeared. I have foundwww.worldtimezone.com/datetime12.php andhttp://24timezones.com/ but neither are as clear or as uncluttered and the site of a few years ago. The terminator has this fascinating shape as we approach the equinox. Regards, Doug --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Terminator
Thanks to Ross, Andrew and Maureen for useful links. A delight to know that someone on the list will respond, even to minor queries. Regards, Doug On 15 Sep 2011, at 09:08, Ross Sinclair Caldwell wrote: > Hi Doug, > > I use "Desktop Earth" - > http://codefromthe70s.org/desktopearth.aspx > > Real-time cloud cover is an option as well > > Ross > > > > From: douglas.bate...@btinternet.com > > Subject: Terminator > > Date: Wed, 14 Sep 2011 22:25:58 +0100 > > To: sund...@rrz.uni-koeln.de > > > > Does anyone know of a link or an "app" that shows the terminator in graphic > > form over the world. > > > > I used to use a 'mapmaker' website but that seems to have disappeared. > > > > I have found www.worldtimezone.com/datetime12.php > > and http://24timezones.com/ > > > > but neither are as clear or as uncluttered and the site of a few years ago. > > > > The terminator has this fascinating shape as we approach the equinox. > > > > Regards, Doug > > > > --- > > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
RE: Terminator
Hi Doug, I use "Desktop Earth" - http://codefromthe70s.org/desktopearth.aspx Real-time cloud cover is an option as well Ross > From: douglas.bate...@btinternet.com > Subject: Terminator > Date: Wed, 14 Sep 2011 22:25:58 +0100 > To: sund...@rrz.uni-koeln.de > > Does anyone know of a link or an "app" that shows the terminator in graphic > form over the world. > > I used to use a 'mapmaker' website but that seems to have disappeared. > > I have foundwww.worldtimezone.com/datetime12.php > andhttp://24timezones.com/ > > but neither are as clear or as uncluttered and the site of a few years ago. > > The terminator has this fascinating shape as we approach the equinox. > > Regards, Doug > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Terminator
Does anyone know of a link or an "app" that shows the terminator in graphic form over the world. I used to use a 'mapmaker' website but that seems to have disappeared. I have foundwww.worldtimezone.com/datetime12.php andhttp://24timezones.com/ but neither are as clear or as uncluttered and the site of a few years ago. The terminator has this fascinating shape as we approach the equinox. Regards, Doug --- https://lists.uni-koeln.de/mailman/listinfo/sundial
RE: Terminator
I've got a little slide show that illustrates the points James makes. The first slide shows the day-night interface as a great circle; the second uses civil sunset; the third and fourth civil and nautical twilight; and the fifth the terminator. I've removed the background map of the world from the last four slides in order to de-clutter them. The compressed file is 320KB and I'm willing to send it off-list to anyone who wants it (I've not enclosed it as an attachment because some list members pay for their connections and downloads; and I don't have access to a website or else I would have posted it). Not surprisingly, given that we are at the equinox, the difference is most pronounced at the poles. Brad -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of James E. Morrison Sent: Tuesday, March 21, 2006 12:11 PM To: sundial@rrz.uni-koeln.de Subject: Terminator Actually, the terminator for civil sunrist/sunset is not a great circle. Sunrise/sunset is defined as the time when the upper limb of the sun is on the theoretical horizon and occurs when the center of the sun is about .835 degrees below the horizon. So, the terminator line for civil sunrise/sunset is a small circle less than a degree from the great circle passing through the center of the sun. This would not be visible on the Sun Clock type presentation of the terminator line. Similarly, the levels of twilight are defined by small circles. Civil twilight ends when the sun's center is 6 degrees below the horizon and is described as when you need artificial light to read a newspaper. Nautical twilight is when the horizon is not visible at sea and is when the sun's center is 12 degrees below the horizon. The true terminator small circle is defined as when the sun's center is 18 degrees below the horizon and there is no light from the sun at all. The 18 degree value has historical roots from Islamic astronomy. All Islamic prayer times are astronomically determined. The "al-'isha" prayer time starts at the end of twilight and ends at daybreak. A crepuscular (i.e. twilight) arc at -18 degrees solar altitude is often shown on astrolabes to mark the end of twilight. Other values such as 19, 20 and 21 degrees were used, but 18 degrees became something of a traditional standard that has endured. The level of twilight is highly subjective and depends on local air quality, cloud cover, etc. Thus, the definitions of twilight level are somewhat arbitrary, but have endured for many centuries. Best regards, Jim James E. Morrison [EMAIL PROTECTED] Astrolabe web site at astrolabes.org --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Terminator
Actually, the terminator for civil sunrist/sunset is not a great circle. Sunrise/sunset is defined as the time when the upper limb of the sun is on the theoretical horizon and occurs when the center of the sun is about .835 degrees below the horizon. So, the terminator line for civil sunrise/sunset is a small circle less than a degree from the great circle passing through the center of the sun. This would not be visible on the Sun Clock type presentation of the terminator line. Similarly, the levels of twilight are defined by small circles. Civil twilight ends when the sun's center is 6 degrees below the horizon and is described as when you need artificial light to read a newspaper. Nautical twilight is when the horizon is not visible at sea and is when the sun's center is 12 degrees below the horizon. The true terminator small circle is defined as when the sun's center is 18 degrees below the horizon and there is no light from the sun at all. The 18 degree value has historical roots from Islamic astronomy. All Islamic prayer times are astronomically determined. The "al-'isha" prayer time starts at the end of twilight and ends at daybreak. A crepuscular (i.e. twilight) arc at -18 degrees solar altitude is often shown on astrolabes to mark the end of twilight. Other values such as 19, 20 and 21 degrees were used, but 18 degrees became something of a traditional standard that has endured. The level of twilight is highly subjective and depends on local air quality, cloud cover, etc. Thus, the definitions of twilight level are somewhat arbitrary, but have endured for many centuries. Best regards, Jim James E. Morrison [EMAIL PROTECTED] Astrolabe web site at astrolabes.org --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Terminator
Douglas Bateman <[EMAIL PROTECTED]> wrote: I have a site on my browser, www.mapmaker.com/shadowfacts/sunweb.asp that shows the terminator throughout the year. It is fascinating to see how rapidly the shape changes, Already the sunclock shows the light is broadening in the northern hemisphere. Not even one full day into spring. Hmmm... There was comment about the terminator being a great circle in actual fact. A Mercator projection shows lines of longitude parallel so the light and dark bands have straight lines between them at the equinoxes. But is the terminator really a great circle and can we tell the difference on the sun clock? The sun is not infinitely far away and on that account less than half the globe would be illuminated. However, the sun's disk subtends ~1/2 degree at the earth which would make more than half the globe illuminated. Finally, due to refraction by the curved atmosphere, we see some piece of the sun's disk before said piece is over the horizon. My question: what is the sum of these effects (and any I have forgotten)? What fraction of the earth's surface can see some part of the sun's disk at any given time? Thanks, John --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Terminator
I hope I won't be seen as a spoilsport if I point out that the shape of the terminator is always a great circle. It is only when the earth's surface is projected onto a flat map that it may appear as a wave. The moral is, don't trust maps. Chris Lusby Taylor 51.4N 1.3W - Original Message - From: "Douglas Bateman" <[EMAIL PROTECTED]> To: Sent: Sunday, March 19, 2006 6:01 PM Subject: Terminator > I have a site on my browser, www.mapmaker.com/shadowfacts/sunweb.asp > that shows the terminator throughout the year. It is fascinating to > see how rapidly the shape changes, and I was astonished to see this > evening that it is nearly a straight line, as we approach the equinox. > > Of course, a little thought shows that I have should have expected > this, but to see it on a 'flat earth' reminds one of what is happening > to a globe, or the earth itself. > > I expect others have more fun with other representations! > > Doug > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
RE: Terminator
There is also a good depiction of the terminator on the under "Current Solar Data" on the NASS Web site. http://sundials.org/ Bob --- https://lists.uni-koeln.de/mailman/listinfo/sundial
RE: Terminator
Another interesting site is: http://www.fourmilab.com/homeplanet/ If you haven't already come across it. Regards Andrew -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Douglas Bateman Sent: 19 March 2006 18:01 To: sundial@uni-koeln.de Subject: Terminator I have a site on my browser, www.mapmaker.com/shadowfacts/sunweb.asp that shows the terminator throughout the year. It is fascinating to see how rapidly the shape changes, and I was astonished to see this evening that it is nearly a straight line, as we approach the equinox. Of course, a little thought shows that I have should have expected this, but to see it on a 'flat earth' reminds one of what is happening to a globe, or the earth itself. I expect others have more fun with other representations! Doug --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
[Fwd: Re: Terminator]
Douglas Bateman wrote: I have a site on my browser, www.mapmaker.com/shadowfacts/sunweb.asp that shows the terminator throughout the year. I Doug https://lists.uni-koeln.de/mailman/listinfo/sundial I have always loved the SunClock display. The changes through the seasons are indeed fascinating... I went to their site, and refreshed my memory of the various displays and products they offer. It's been a long time since I had a copy on my PC, and while I don't want it as a screensaver, I thought it would be nice to have the executable version again. G!! As I started to install it, my anti-spyware popped up and informed me LOPDOTCOM was trying to install itself. This is a particularly nasty commercial hijacker, that I doubt any of us wants on the desktop... http://anti-spyware-review.toptenreviews.com/spyware/lop.html Be warned, be aware, be safe! Dave --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Terminator
Thank you Doug, Another one very different but interesting too on the equinox day, have a look on my favorite sundial, in the South of France http://perso.wanadoo.fr/cadrans.solaires/cadrans/cadran-mines.html Joël 48°01'25'' N, 1°45'40" O > http://www.cadrans-solaires.fr/ - Original Message - From: "Douglas Bateman" <[EMAIL PROTECTED]> To: Sent: Sunday, March 19, 2006 7:01 PM Subject: Terminator I have a site on my browser, www.mapmaker.com/shadowfacts/sunweb.asp that shows the terminator throughout the year. It is fascinating to see how rapidly the shape changes, and I was astonished to see this evening that it is nearly a straight line, as we approach the equinox. Of course, a little thought shows that I have should have expected this, but to see it on a 'flat earth' reminds one of what is happening to a globe, or the earth itself. I expect others have more fun with other representations! Doug --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Terminator
I have a site on my browser, www.mapmaker.com/shadowfacts/sunweb.asp that shows the terminator throughout the year. It is fascinating to see how rapidly the shape changes, and I was astonished to see this evening that it is nearly a straight line, as we approach the equinox. Of course, a little thought shows that I have should have expected this, but to see it on a 'flat earth' reminds one of what is happening to a globe, or the earth itself. I expect others have more fun with other representations! Doug --- https://lists.uni-koeln.de/mailman/listinfo/sundial
