Consulting on Sun Oriented Sculpture

Bill Gottesman, Burlington, Vermont

Burlington Earth Clock

Pagan Cross Quarter Days

The Problem: Calculate position of stones for sunset on the Equinoxes, Solstices, and cross quarter days , and atmospheric refraction.

, accounting for the variable height of the mountains

Height of Horizon affects setting azimuth of the sun

Atmospheric Refraction makes the sun appear up to ½ degree higher than its calculated value based

on date and time.

What to do?

1. Observe and mark the sunsets over a 1 year period.

2. Figure something else out.

1. Photograph the horizon. Then use the exact time of the photo to determine the sun’s altitude and azimuth.

2. Calculate roughly the azimuths of desired setting suns.3. Measure the altitude of these azimuths from the photograph.

4. Now you can accurately calculate the azimuth of the setting sun (this is what you wanted).

Again, with a bit more detail

Photograph horizon at camera’s neutral focal length, or with zoom, to avoid distortion. Then manually stitch photos together with Photoshop

Using Photoshop’s layers feature, superimpose photos of the sun near the horizon. Label the time and date of each sun image

Calculate the Altitude and Azimuth of each sun using Dialist Companion, or other spreadsheet. I wrote “Sun Position Calculator.xls” for this purpose. It is free at my Precision Sundials website.

Calculate the Altitude and Azimuth of each sun using Dialist Companion, or other spreadsheet. I wrote “Sun Position Calculator.xls” for this purpose. It is free at my Precision Sundials website.

Make a measurement scale for altitude and azimuth

Determine the altitudes and azimuths for the sunsets on your key dates

Use an average altitude to calculate an rough azimuth value for a given date (use mean year of 2002, 2006, etc).

Use photoshop to get an accurate horizon altitude for the estimated azimuth

Now enter revised horizon altitude into spreadsheet, to get an accurate calculation of azimuth.

Make your final correction on the photo

What do you consider sunset?

Lollipop Half-set Quarter-set

A theodolite is great for finding north, and laying out the angles