Examples for determining latitudes.
Copenhagen 13'th of August 2001 (decl. = 14.55, sunhight at noon = 48,4 dg.)
Gnomon (pencil) showing curves for 25'th of April and 13'th of August in Copenhagen (Latitude aprox. = 56 dg. north, declination ref. tabel aprox = 15 dg.).
Piece of wood pointing towards the sun untill the shadow disappear.
|If you can't see any shadow (when the sun is still shining) make the projection of the triangle.|
Measure the angle between the wood and the table (in this example 48,4 dg.).
Latitude = 90 - angle + decl. = 90 - 48,4 + 14,5 = 56,1 dg. north.
The vikings gnomon was more accurate than my piece of wood.
If you are doing the measurement around equinox you dont have to worry about the declination (= 0). The Vikings used that knowledge.
Declination over the year (the vikings used sunradiens (half wheels) for measurement. See table below for a modern expression.):
|-22° til -17°||-17° til -8°||-8° til 4°||4° til 15°||15° til 22°||23°|
|22° til 17°||17° til 8°||8° til -4°||-4° til -15°||-15° til -22°||-23°|
Model of a horisontal placed compass seen from East (based on 62 degrees North). Sun is rising NEtE around 13'th of August.
Sun hight at Copenhagen (56NB) at noon the 13'th of August computersimulated (sun is rising around NEtE):