How to read a sun path diagram
Imagine lying on your back and looking straight up: the diagram is the dome of the sky squashed flat. The centre is the zenith, directly overhead; the outer circle is the horizon. Rings mark the sun's elevation in 15° steps, and the spokes mark its azimuth — north at the top, east to the right.
Each curve is one day's journey. The outermost curve on the sunny side belongs to the winter solstice — the sun rises far to the south-east, stays low and sets in the south-west (in the northern hemisphere). The innermost belongs to the summer solstice. Every other day of the year lies between the two, and each day appears twice: once as the days lengthen and once as they shorten.
The dots are clock hours. Where they sit on a curve tells you both the direction and the height of the sun at that hour.
What it is used for
- Solar panels. Mark a tree, chimney or neighbouring roof on the diagram by its direction and angular height; wherever it covers the winter curve, it shades your array in winter.
- Architecture. Size overhangs that block the high summer sun and admit the low winter sun; place windows for morning or evening light.
- Gardens. Find which beds get six hours of direct sun in June and which lose it by September.
- Photography. Plan where the sun will set behind a landmark on a given date.
For an interactive version drawn over a map of your site, use the sun map: the same curves are drawn around the observer, to the true directions of your street.