Hi Rudolf & other shadowwatchers Not a place for my holidays. 49.37 S 135 W is somewhere half between the south-points of New Zealand and South-America. The weatherforecast for the region is a sunny day and temperature about -5 degrees Celsius. A cold place at sea, but perhaps we can see the sunrise and the sunset when it is not too hazy.
Hein van Winkel 52 05 N 4 24 E -----Oorspronkelijk bericht----- Van: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Namens R.Hooijenga Verzonden: maandag 13 juni 2005 23:21 Aan: [email protected] Onderwerp: RE: Deriving Lat & Lon from Sunrise & Sunset Hello sundialeers, I think I could guess the basics behind the method Brooke describes. >From sunrise and sunset, get noon. True noon,corrected with EOT and expressed in UTC, would give you longitude, thus: NOON(utc) - 12 hours = (degrees WEST) / 15 >From sunset and sunrise, we also have the half daylight length t, for which we have our T-shirt formula: - cos(t) = tan(decl) tan(lat) which we solve for lat. How sunset and sunrise are determined, I don't know (yes, a photocell, but what constitutes "sunset"? In Holland, it does not get dark anytime during the night, this time of year - then again, it certainly is a lot darker that during the day, even if it is raining again). Example Assume we see a sunrise at 17:00 utc and a sunset at 01:00 (which is conveniently written as 25:00); we get noon = (25+17)/2 = 21.00 utc. eot is about zero today (June 13), so we get corrected noon is also 21.00 utc longitude = (15*21 -12) degs West, or 135 degs West. Also, t = (25-17)/2 = 4 hours. Now the half day length is 4 hours, corresponding to 60 degrees. The declination of the sun is 23.23 degrees north today, so: - cos (60) = tan(23.23) tan(lat) -0.5 = 0.429 tan (lat), so that tan (lat) = -1.166 and finally lat = -49.37 degrees, or 49.37 degs South Our animal was at 49.37 South, 135 West today - wherever that may be. Rudolf -----Oorspronkelijk bericht----- Van: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Namens Brooke Clarke Verzonden: maandag 13 juni 2005 21:06 Aan: [email protected] Onderwerp: Deriving Lat & Lon from Sunrise & Sunset Hi: There is an animal tracking system that records the times of sunrise and sunset (along with the date and time) and then sends that (and some other stuff) to a central station. In the central station they process the sunrise and sunset times to find out the Lat and Lon of the animal (maybe to 1 degree). - -
