Calculating sunrise and sunset between two points

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UncleRob U
UncleRob Dec 7, 2008 13:44:53
Replying to tiompan

The more one thinks about this question the worse it gets! I never got on with trigonometry, very confusing. I reckon there must be a site out there that does more flexible calculations of sun position. Given the Ordnance Survey Eastings and Northings (and elevation) of the passage tomb and the hill, you could work out the azimuth and elevation of the hill top from the tomb. Then you want to know when the sun passes through that point. Hmmm, I bet there are a few astronomy chatrooms out there where they would know how to get the answer straight away. (But, as AuntCaroline would say, Nerd Alert!)

U UncleRob
UncleRob Dec 7, 2008 14:13:52
Replying to UncleRob

Have given this a little more brain power... deep breath...

azimuth (angle from North, counting clockwise) = arctan((Easting of hill - Easting of tomb) / (Northing of hill - Northing of tomb))
Arctan is the inverse tangent and you can get that off the old Windows calculator accessory if you don't have a scientific calculator. Usualy there is a small adjustment mentioned on the map somewhere to bring the grid into line with True North (not magnetic north!)

Similarly for the elevation: arctan((height of hilltop - height of tomb) / distance as crow flies from tomb to hill)

I always feel the need to apologise after getting mathematical, but hopefully this will do the trick for the first part of the puzzle. Send me the numbers if you get stuck!

Rob

T tiompan
tiompan Dec 7, 2008 14:32:14
Replying to UncleRob

UncleRob wrote:
The more one thinks about this question the worse it gets! I never got on with trigonometry, very confusing. I reckon there must be a site out there that does more flexible calculations of sun position. Given the Ordnance Survey Eastings and Northings (and elevation) of the passage tomb and the hill, you could work out the azimuth and elevation of the hill top from the tomb. Then you want to know when the sun passes through that point. Hmmm, I bet there are a few astronomy chatrooms out there where they would know how to get the answer straight away. (But, as AuntCaroline would say, Nerd Alert!)
Working from OS maps is not too accurate , although Thom was not averse . What is imporatnt is the declination which includes all the info , heights , distance ,latitude , and azimuth . That info is the minimum then there is the much smaller problems of refraction and parallax .The formula as given by Ruggles etc is
sin latitude sin height+cos latitude cos height cos azimuth =sin declination

it is sunday so sorry about that .