A sun path diagram is a flat map of where the sun appears in the sky throughout the day and year for a specific location on Earth. It plots two coordinates: how high the sun sits above the horizon (elevation) and which compass direction you’d face to see it (azimuth). Once you understand these two axes, reading any sun path diagram becomes straightforward.
The Two Coordinates: Elevation and Azimuth
Every sun path diagram is built on the same pair of measurements. Elevation angle describes how high the sun is above the horizon. Zero degrees means the sun is right at the horizon line, as during sunrise or sunset. Ninety degrees means the sun is directly overhead. Azimuth describes the sun’s compass direction measured clockwise from north. North is 0°, east is 90°, south is 180°, and west is 270°. The scale runs from 0° to 360° in a full circle.
When you look at a diagram and find a point where the sun sits at, say, 58° elevation and 180° azimuth, that means the sun is 58 degrees above the horizon and positioned due south. These two numbers together pinpoint the sun’s exact location in the sky at any moment.
Polar vs. Cylindrical Diagrams
Sun path diagrams come in two common formats, and they display the same information in very different visual layouts.
A polar (stereographic) diagram looks like a target or bullseye viewed from above. The outermost circle represents the horizon at 0° elevation, and the center represents 90°, directly overhead. Azimuth runs around the perimeter like a compass. Each sun path for a given date appears as a curved arc across the circle. This format gives you an intuitive, bird’s-eye view of the entire sky dome, and it’s the most widely used version in architecture and solar design. One drawback: the concentric rings get tightly packed near the center, making it harder to read elevation angles above about 60°.
A cylindrical (Cartesian) diagram looks like a standard graph. The horizontal axis shows azimuth from east to west, and the vertical axis shows elevation from 0° at the bottom to 90° at the top. Sun paths appear as humped curves, peaking at solar noon. This format makes it easy to read exact angles because you’re just reading off a grid, but the curved sun paths can look unfamiliar at first.
Finding the Date Lines
The curved lines sweeping across a sun path diagram each represent the sun’s journey on a specific date. Most diagrams show paths for the 21st of each month, which captures the key seasonal boundaries.
Three paths matter most. The summer solstice line (June 21 in the Northern Hemisphere) is the longest arc. It stretches farthest across the diagram because the sun is above the horizon for the most hours and climbs to its highest point. On a polar diagram, this is the innermost arc, closest to the center. The winter solstice line (December 21) is the shortest arc, representing the fewest daylight hours and the lowest peak elevation. On a polar diagram, it’s the outermost arc, hugging the edges near the horizon. The equinox lines (March 21 and September 21) fall right between these two extremes. All the other monthly paths fan out between the solstice boundaries.
In the Southern Hemisphere, the pattern flips: the June solstice produces the short, low arc and the December solstice produces the tall, wide one.
Reading Time on the Diagram
Crossing the date lines, you’ll see another set of lines or labeled dots marking hours. These typically run roughly perpendicular to the date arcs, connecting the same clock hour across different months. So if you follow the “10 AM” line, you can see where the sun sits at 10 AM on every date shown in the chart.
To find the sun’s position at a specific moment, locate the date line closest to your day of interest, then find where the correct hour mark falls on that line. Read outward (or downward on a cylindrical chart) to get the elevation angle, and read around the perimeter (or across the horizontal axis) to get the azimuth. That intersection is the sun’s position in the sky.
Solar Time vs. Clock Time
Most sun path diagrams use solar time, not the clock time on your phone. Solar noon, when the sun reaches its highest point, happens at the moment the sun is due south (in the Northern Hemisphere). That rarely lines up with 12:00 PM on your clock.
The difference between solar time and local clock time can be as much as 45 minutes in either direction, depending on the time of year and where you sit within your time zone. If you live on the western edge of a time zone, solar noon arrives well after 12:00 PM. Daylight saving time shifts it by another hour. When using a sun path diagram for real planning, you’ll need to account for this offset to get accurate results. Online calculators for your specific location can tell you the current difference.
How Latitude Changes the Picture
A sun path diagram is generated for a specific latitude, and the diagrams look dramatically different as you move north or south. At a mid-latitude city like Tucson (32° N), the sun reaches 81.5° above the horizon on the summer solstice, nearly overhead, and drops to only about 35° at the winter solstice. Summer days last about 14 hours while winter days shrink to 10.
Move closer to the equator and the seasonal difference narrows. The summer and winter arcs crowd together, and peak elevations stay high year-round. Move toward the poles and the arcs spread dramatically apart. Winter paths become very short and low, while summer paths stretch across most of the sky. At extreme latitudes, winter date lines may not appear on the diagram at all because the sun never rises above the horizon on those days.
On the equinoxes, regardless of latitude, the sun rises exactly due east and sets exactly due west. This is a useful landmark when orienting yourself on any diagram. In summer, sunrise and sunset shift toward the northeast and northwest. In winter, they shift toward the southeast and southwest.
North Orientation and Compass Alignment
Sun path diagrams are oriented to true north, not magnetic north. If you’re comparing the diagram to compass readings taken on-site, you need to account for magnetic declination, the difference between where a compass needle points and true geographic north. In some parts of the United States, this offset is over 15°, enough to significantly misalign a shading analysis. The U.S. Geological Survey provides declination values by location.
Using the Diagram for Shading Analysis
One of the most practical uses of a sun path diagram is figuring out when and where shadows will fall on a site. The process involves creating a “shading mask,” an outline of everything that blocks the sky as seen from a specific point on your property.
The simplest method is a horizon survey. Stand at the point you care about (a future solar panel location, a garden bed, a window) and measure the elevation angle and compass direction of every obstruction along the skyline: rooftops, trees, ridgelines. Plot those points onto the sun path diagram. Everything below your obstruction line has sun. Everything above it is blocked.
A faster alternative uses fisheye photography. A fisheye lens captures the entire sky dome in one circular image. When that image is overlaid on a polar sun path diagram, you can immediately see which sun paths are blocked and during which hours. Trees, neighboring buildings, and terrain all show up as dark shapes crossing the sun’s arcs.
Either way, the result tells you exactly which months and hours your site receives direct sunlight. This is essential for sizing solar panels, designing building overhangs, planning gardens, and evaluating passive heating potential. A location that gets full sun in summer but is shaded from October through February, for example, will show up clearly: the winter date lines will fall behind the obstruction outline while the summer lines remain in the clear portion of the chart.