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Thorfinn
01-04-2012, 06:44 AM
Hi all,

I would be grateful for some help. Not sure if this is the best forum for this question, but I'll give it a try and see if anyone can help.

I am looking for a map which would show sunset or sunrise times by location on the equinox. I guess it would be similar to a time zone map, but much more detailed. I guess it would entail "bands" showing zones in which time sets between given times (say between 21h00 and 21h30, 20h30 and 21h00 etc...) at local time. I need it to illustrate the differences in real local sunset times within a time zone. Such a map would be somewhat laborious to create, but i would have thought that there must be something similar out there.

Any help would be appreciated, even if it is just pointing me somewhere else.

Thanks very much.

Thorfinn

Redrobes
01-04-2012, 08:04 AM
It will look like this:

http://www.daylightmap.com/?lat=0.000000&z=2&t=s&c=1&s=1&m=a&hl=en

All you need is the equations for daylight on a Mercator projection. If the earth were not tilted then it would just be vertical bands since it would relate to longitude but since the earth is tilted then you get this wavy line. You could use the web site link to generate a lot of images for the equinox for different places and estimate the curves.

EDIT: Actually, specifically just for the Equinox, you do have straight lines since thats the date where the earth is not tilted. So your sun rise and sun set times are related to the longitude exactly. So for example at Grenwich 0 deg then 12Oc is midday and 6am and 6pm is the sun rise/set times and it will shift around the world 360deg in 24h so its dead simple.

Thorfinn
01-04-2012, 01:24 PM
Thanks for your reply.

However, that isn't exactly what I'm looking for. I need something that will show the local time of the sunset. This is no easy task because of the political nature of time zones, as well as the changes in relative times because of the size of time zones. But it wouldn't be all that hard to create with the correct data and tools.