Looking for date-lines

If we want to examine a location to find out its relation with the Sun many difficulties appear.

Point of sunrise

The point of sunrise (and sunset) on a specific date depends on the latitude. On the latitude 51° NB the Sun will rise in the northeast during midsummer, about 50 degrees from north. Midwinter sunrise (December 22) will be seen southeast, about 130 degrees from north.
The angles for sun rise and sunset on any latitude can be calculated whit a mathematic formula, but this doesn't lead to a complete solution...

We also have to in calculate the observation point's height. Seen from a high mountain sunrise will be earlier. Also the horizon influences the result, a hill can hide the rising Sun.

Possible a sight line is not orientated to the point of sunrise, but on a later moment for example after morning fog dissolved. Maybe original they used a now disappeared vizier point.

If we want to examine an old alignment, we also have to calculate precession. Fife thousand year ago megalith builders saw sunrise about one degree more north (See on next page precession).

New building and plantations often made observations impossible.

And last but not least, accurate measurements acquire expensive instruments or a lot of creativity... 

Computer programs

Fortunately exist many computer programs to do the calculations saving us from a headache...
"Stellarium" is an excellent software program that calculates more than only solar positions.
Furthermore it's free software easy to download. --> www.stellarium.org
Alas you can't use "Stellarium" to go back 5000 year in time...

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