Without using a computer...
Or your phone!
Basically, the answer is: use Vitruvius' analemma.
To save me repeating the method.
Go to this page first: How to make the analemma link...
Then come back.
The analemma was designed to use a shadow length taken at midday on the equinox. But as long as you know your latitude, you don't have to wait until midday at the equinox to go out and construct the analemma.
I used a latitude of 50 and a drawing program to make the image..but the number is gives for summer solstice azimuth isn't far off.
Point S is where the ecliptic line crosses the horizon.
Point D gives the azimuth.
Now just as a thought experiment, if I wanted to make a stone circle to predict where the sun would rise, how would I go about it? Clearly it is easier just to make a circle and to mark sun rise positions on it....but what if predicting such things would give you kudos...
Start with what we have.
Again, imagine the Sanctuary.
The circle to the ring of blue markers measures approximately 45 feet, across.
So, how long would the shadow be from a 22 foot, 6 inch pole placed at the east edge of the circle be at midday at the equinox?
Latitude = 51.41
Call it 51 (!)
Elevation angle of the midday sun 90 degrees - latitude = 39.
Length of post divided by tangent of elevation angle is...
270 inches / 1.234897 = 218.64 inches
= 18 foot or so...
Which isn't too bad, you could use that!
But you would have to record the length and draw the shadow line from south eastward, then add the meridian, horizon and equator lines, and then draw another arc to represent the horizon...
:)
Or your phone!
To save me repeating the method.
Go to this page first: How to make the analemma link...
Then come back.
The analemma was designed to use a shadow length taken at midday on the equinox. But as long as you know your latitude, you don't have to wait until midday at the equinox to go out and construct the analemma.
I used a latitude of 50 and a drawing program to make the image..but the number is gives for summer solstice azimuth isn't far off.
Point S is where the ecliptic line crosses the horizon.
Point D gives the azimuth.
Now just as a thought experiment, if I wanted to make a stone circle to predict where the sun would rise, how would I go about it? Clearly it is easier just to make a circle and to mark sun rise positions on it....but what if predicting such things would give you kudos...
Start with what we have.
Again, imagine the Sanctuary.
The circle to the ring of blue markers measures approximately 45 feet, across.
So, how long would the shadow be from a 22 foot, 6 inch pole placed at the east edge of the circle be at midday at the equinox?
Latitude = 51.41
Call it 51 (!)
Elevation angle of the midday sun 90 degrees - latitude = 39.
Length of post divided by tangent of elevation angle is...
270 inches / 1.234897 = 218.64 inches
= 18 foot or so...
Which isn't too bad, you could use that!
But you would have to record the length and draw the shadow line from south eastward, then add the meridian, horizon and equator lines, and then draw another arc to represent the horizon...
:)
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