A sun path diagram in architecture is a chart that plots the position of the sun, given as azimuth and altitude, for every hour of the day across the year at one latitude. Architects read it to predict shadows, sunlight hours and glare, then set building orientation, shading depth and glazing area from what the chart shows.
Almost every studio project asks for one, and almost every student draws it as decoration. The chart earns its place only when it gives you a number you can build with, such as how deep an overhang has to be.
What Is a Sun Path Diagram?
Picture the sky as a dome over your site. The sun traces a curve across it each day, and that curve shifts through the year. A sun path diagram flattens the dome onto paper so the whole year fits in one drawing: curved lines are the daily paths, usually drawn for the 21st of each month, and the lines crossing them mark the hours.
The chart is site specific, not building specific: latitude sets the geometry, so a diagram for Lisbon is useless in Oslo while two projects in one city share one. Generate one for any coordinates with the Sun Path Chart Program from the University of Oregon Solar Radiation Monitoring Laboratory, which draws Cartesian or polar charts from coordinates or a US zip code. For a single moment rather than a whole year, the NOAA Solar Calculator returns sunrise, sunset, solar noon, azimuth and elevation. NOAA notes there that the tool is no longer maintained, so treat it as a quick check.
The drawing sits upstream of most environmental work. Sun path analysis precedes any serious daylighting strategy, because you cannot size a light shelf without knowing where the sun is.
Azimuth and Altitude: The Two Angles Behind Every Chart
Every point on the chart is a pair of angles. Azimuth is the sun's compass bearing, measured clockwise from true north, so 90 degrees is east, 180 south and 270 west. Altitude, or elevation, is how high the sun sits above the horizon, from 0 to 90 degrees overhead. NOAA defines the pair the same way in its solar calculator glossary.
Those two numbers place a shadow: azimuth gives its direction, altitude its length. A sun at 15 degrees altitude throws a shadow roughly 3.7 times the height of the object casting it, while a 60 degree sun cuts that to about 0.58 times the height.
📐 Technical Note
Solar noon altitude follows one formula: 90 minus your latitude plus the sun's declination, which swings between plus and minus 23.44 degrees over the year. At latitude 40 north that is roughly 73.4 degrees in June and 26.6 in December. Run both before opening software; if the chart disagrees, you entered the wrong location.
Stereographic and Cylindrical Charts: How to Read Each One
The same data gets flattened two ways. A stereographic chart, usually called polar, projects the sky dome onto a circle seen from above: the centre is the zenith, the outer ring the horizon, compass directions around the edge. A cylindrical chart, often labelled Cartesian or orthographic, unrolls the horizon into a straight line with azimuth across and altitude up.
Polar charts read like a plan, which is why they dominate solar access and shadow mask work. Cylindrical charts read like an elevation and line up with a facade drawing. Neither is more accurate.
At a Glance: Polar and Cylindrical Charts Compared
| Aspect | Stereographic (Polar) | Cylindrical (Cartesian) |
|---|---|---|
| Shape | Circle, horizon at the outer ring | Rectangle, horizon along the base |
| Reads like | A plan view of the sky | An unrolled elevation |
| Best use | Solar access, courtyards, roof studies | Facade shading, obstruction profiles |
| Weak point | Hours crowd near the centre in summer | Direction is less intuitive at a glance |
| Overlay onto | Site plan, shadow mask | Facade elevation, panorama photo |
How Does Latitude Change the Diagram?
Latitude decides how tilted the daily paths are and how high the summer arc climbs. Near the equator the paths run steeply, the sun reaches almost overhead at midday, and day length barely changes. Move toward the poles and the arcs flatten, the spread between the solstice curves widens, and the gap between June and December becomes the dominant design problem.
Shading rules therefore do not travel. A horizontal overhang works at mid latitudes on an equator facing wall because the summer sun is high and the winter sun low. Near the equator that logic fails on east and west walls, where the sun is low and nearly square to the glass twice a day all year.
Equinox, Solstice and Hour Lines
Three curves carry most of the information. The solstice paths, around 21 June and 21 December, bound the annual range, and every other day falls between them. The equinox path sits in the middle. On the equinoxes the sun rises due east and sets due west at essentially every latitude, a quick check that your chart is oriented correctly.
Hour lines cross the daily paths and mark solar time, not the time on your phone. Where an hour line meets a date curve you have one specific sun position, the input for a shadow study.
📌 Did You Know?
Solar noon and clock noon rarely agree. The equation of time, published by the NOAA Solar Calculator, swings by roughly a quarter of an hour either way over the year because the Earth's orbit is elliptical and its axis tilted. Add a time zone offset and daylight saving, and the sun can peak more than an hour from 12:00.
From Diagram to Shadows and Sunlight Hours
A chart on its own is only data. Overlaying the site's obstructions onto it produces a shadow mask, also called an obstruction profile, and anything hidden behind that mask is a moment when the sun is blocked.
The field method is analogue. The University of Oregon lab describes it in its notes on sun path charts: stand at the point you care about, read each obstruction's azimuth with a compass and its elevation with a clinometer, then plot the pairs. The lab also flags the correction that catches people out, since a compass reads magnetic north while charts are drawn to true north.
Counting is then simple. Follow the winter solstice curve from sunrise to sunset, add up the hours clear of the mask, and you have the shortest day's direct sunlight at that point. Repeat for a window sill or a courtyard and you compare options with a number, not an opinion.
Turning the Diagram into Design Decisions
Orientation. Read where the sun sits during occupied hours. An office skin facing the late afternoon sun in a hot climate fights a low, hard to shade angle every working day, and rotating the plan costs nothing at concept stage.
Shading depth. Pick a cut-off altitude, meaning the angle above which you want the glass shaded, then divide the window height by the tangent of that angle. A 2 metre high window shaded above 60 degrees needs roughly 1.15 metres of overhang. The same geometry sets the depth and spacing of fins on a brise-soleil.
Glazing area. Facades with heavy summer exposure and little winter gain rarely justify large openings. The ASHRAE Handbook chapter on fenestration sets out the hierarchy: shades on the outdoor side of the glazing cut solar heat gain far more effectively than indoor devices, and reveals, fins and overhangs do it without the maintenance burden. External geometry keeps the openings you want, the argument behind most passive cooling work.
💡 Pro Tip
Do not size an overhang from the solstice alone. Peak cooling load lands weeks after the June solstice, when the sun is lower but ground and air are hotter, so a shade tuned to 21 June leaves that period exposed. Test early August too, then take the deeper result.
Presenting Sun Path Analysis on a Site Analysis Board
These drawings fail on juries for graphic reasons more often than technical ones. A rainbow of arcs over a grey plan says nothing. Reduce the chart to your argument: two or three date curves, hour marks only where you reference them, and one highlighted moment such as the winter afternoon that set your massing.
Put the consequence beside it. A solstice sun path next to a shadow plan of the same date, or beside the section showing the overhang it produced, reads in two seconds. That discipline runs through a good site analysis for architecture students, where every drawing leads somewhere. For a consistent graphic language, the diagram resources in our shop include site analysis and solar components.
Mistakes That Ruin a Sun Path Study
- Using a northern hemisphere chart below the equator, where the sun tracks through the north and every shading device flips to the opposite facade.
- Aligning the chart to plan north or magnetic north rather than true north. A 10 degree error moves every shadow in the project.
- Reading hour lines as clock time. Charts use solar time unless the software says otherwise, and daylight saving adds another hour.
- Testing only the solstices, when the equinox and late summer often govern the real comfort problem.
- Copying a chart from a nearby city without checking latitude, since a few degrees changes the winter arc.
Frequently Asked Questions
What Is the Difference Between a Sun Path Diagram and a Solar Analysis Diagram?
A sun path diagram shows solar geometry alone: where the sun is at a given date and hour for one latitude. A solar analysis diagram applies that geometry to a site and reports a result, such as shadow extents or hours of direct sun. The first is an input, the second an output.
Which Dates Should I Use for a Shading Study?
Test three: the summer solstice, the winter solstice and an equinox. Add a late summer date in a cooling dominated climate, because peak heat arrives after the sun has started dropping.
Why Does My Chart Look Flat Compared to My Classmate's?
Latitude. Sites near the equator give steep, tightly packed paths with a high midday sun, while higher latitudes give flattened arcs with a wide spread between the solstice curves. Confirm the latitude used before assuming anything is wrong.
Can a Sun Path Diagram Tell Me How Much Energy a Facade Receives?
Not directly. The chart gives geometry, not intensity. Radiation depends on atmospheric conditions and cloud cover, which come from measured climate data, so pair the chart with a weather file for energy figures.
Where to Go From Here
Your Next Step: Generate a chart for your project's exact coordinates, mark the winter solstice curve, and count the clear sunlight hours at the one place in your scheme you care about most. That number tells you more about the massing than another week of iteration.
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