This post is about making sure my new garden beds don’t end up in the shadow of my back porch, during the summer. Based on the length of the shadows today, in late winter. And, ultimately, based simply on the height of the porch roof.
To cut to the chase: If you use Excel, and the NOAA sun-angle calculator, you can accurately predict the length of a shadow, for any date and time, anywhere on earth, via this formula:
Shadow length = obstruction height * cotangent (solar elevation angle in degrees * π / 180)
The π / 180 is there because Excel wants to see angles expressed in radians. If you’re using a calculator that accepts angles in degrees, omit that.