Sun-path diagram generator

What a sun path diagram shows

A sun path diagram is a polar chart that plots the sun's position across the sky for a given place and date, using two angles: altitude above the horizon and azimuth around the compass. This generator draws the path for any latitude, longitude and date you choose, together with the June 21 and December 21 solstice paths, which bound where the sun can ever be at that location.

Architects and designers use sun paths to orient buildings, place windows, size shading and check which parts of a site get winter sun. The diagram answers questions such as: where does the sun rise in midwinter, how high is it at noon in summer, and which facades see low evening sun?

Positions are calculated in your browser with the SunCalc library from UTC time, latitude and longitude. The result panel also reports sunrise, sunset, solar noon and day length for the date and both solstices, and you can mask neighbouring buildings or trees as obstructions to see how many hours of direct sun survive. Download the diagram as SVG or PNG, and the hourly altitude, azimuth and sun times as CSV.

How to use the sun-path diagram generator

1. Pick a city from the built-in list of more than 100 cities, or choose Custom coordinates and type your own latitude and longitude. Positive latitude is north and positive longitude is east, so New York is 40.7128, −74.0060. The list is stored with the tool; nothing is looked up online.
2. Choose the date to study. It is drawn as the dark curve. The amber curve is June 21 and the grey curve is December 21 of the same year.
3. Check the UTC offset. For a city it is worked out for that date from its IANA time zone, so daylight saving is already included (New York in July shows −4). Edit the field to override it, or choose Use the time-zone offset to return to automatic.
4. Switch the projection between equidistant (evenly spaced 30° and 60° rings) and stereographic (the sky-dome projection used on most printed sun-path charts).
5. Add up to eight obstructions, each with a label, the azimuth band it covers (clockwise from north, wrapping past 360°) and its altitude. They are shaded on the diagram, blocked hours are drawn as hollow dots, and the result panel reports sunlit and blocked hours for the date.
6. Read the result panel: sunrise, sunset, solar noon and day length in local clock time, with the same figures for both solstices under Sunrise & sunset at the solstices. On the diagram the center is the zenith, the outer ring is the horizon, and dots mark every two hours in local time.
7. Open Hourly positions for altitude, azimuth and sky status at each hour, then download the diagram as SVG or PNG, or the sun times, obstructions and hourly data as a CSV.

Worked example

At the equator near the March equinox, the sun passes close to the zenith around solar noon.

How to read a sun path diagram

The chart is laid out like a site plan with north at the top, east on the right, south at the bottom and west on the left. The outer circle is the horizon (0° altitude) and the center is directly overhead (90°). A point halfway between them is 45° above the horizon.

Each curve is one day. In mid-northern latitudes the sun rises in the east, passes to the south and sets in the west. In the southern hemisphere it passes to the north, which is why the default Auckland diagram bows toward the top of the chart.

To find the sun at a given time, find that hour's dot on the curve. Its direction from the center is the azimuth, and its distance in from the outer ring is the altitude. The hourly table gives exact values.

The band between the amber June curve and the grey December curve is the part of the sky the sun crosses during the year. Sky outside that band never receives the sun at that latitude, which is useful when judging which openings can ever see direct sun.

Solar altitude and azimuth explained

Altitude is the sun's angle above the horizon, from 0° at sunrise and sunset to its maximum at solar noon. Azimuth is its compass direction, measured in this tool clockwise from true north: 90° is east, 180° is south and 270° is west. Some software measures azimuth from south instead, so check the convention before copying values between tools.

Altitude sets shadow length and how deep sun reaches into a room. Azimuth tells you which facade the sun is striking. Together they are the inputs to the shadow length and overhang calculator. For a longer primer, see solar altitude and azimuth explained.

Solstice and equinox sun angles by latitude

Noon altitude follows a simple rule: 90° minus the difference between your latitude and the sun's declination. Declination is about +23.44° at the June solstice, 0° at the equinoxes and −23.44° at the December solstice. At the equinoxes the sun rises close to due east and sets close to due west everywhere.

The table uses those geometric formulas for northern latitudes. It ignores atmospheric refraction, which lifts the apparent sun near the horizon and adds a few minutes of daylight, so treat the values as design approximations. Below 23.44°N the June noon sun passes north of overhead, so the 0° and 20° June values are measured toward the north. For the southern hemisphere, swap the June and December columns.

Worked example: New York sun path at the solstices

With New York selected (40.7128, −74.0060) and the offset overridden to UTC−5 for both dates, the tool's hourly positions show the sun peaking at about 72.7° on June 21 and about 25.8° on December 21. The difference, roughly 47°, is twice the 23.44° tilt of Earth's axis.

At 8:00 standard time on June 21 the sun is already 37.8° high and almost due east. At the same hour on December 21 it is only 5.9° high in the southeast. An east-facing room gets strong morning sun in summer and low, grazing sun in winter.

The UTC offset matters. Choose New York for June 21 and the offset becomes −4 automatically because daylight saving is in force, so solar noon lands near 12:59 on the clock; override it to −5 and the same instant reads 11:59. The table below uses UTC−5 for both dates so the June and December columns line up. City-specific figures are in sun path and solar angles for New York.

Who it is for and when to use it

Method, formulas & assumptions

SunCalc computes solar altitude and azimuth from UTC instants, latitude and longitude. The polar chart maps zenith to the centre and the horizon to the outer ring.

Solar position engine: SunCalc 1.9.0.

Common mistakes to avoid

• Overriding a city's automatic UTC offset with standard time for a summer date. Every hour label shifts by one when daylight saving applies, so leave the offset on automatic unless you have a reason not to.
• Confusing true north with magnetic north. The diagram uses true north; a compass reading on site needs correcting for local magnetic declination.
• Entering west longitudes as positive. Locations in the Americas have negative longitude, and a sign error moves the site to the other side of the world.
• Assuming azimuth is measured from south. This tool measures clockwise from north, so due south is 180°.
• Treating the open-sky diagram as a shading study. Enter neighbouring buildings, trees or terrain as obstructions (an azimuth band and an altitude) before reading the sunlit hours; anything you do not enter is not modelled.
• Reading June and December the wrong way round in the southern hemisphere. In Auckland or Sydney the high summer path is the December curve.

Scope & limits

City presets derive the UTC offset, including daylight saving, from the time zone; custom coordinates need a fixed offset for the selected date. Obstructions are simple azimuth bands you enter; the diagram excludes terrain and detailed atmospheric effects.

Frequently asked questions

Further reading

• Sun path diagrams by city
• Solar altitude and azimuth explained
• Sun path and solar angles in New York
• Solar data by location
• All site & solar tools
• All free architecture & construction tools
• Harth resource library

In this category

• Floor area ratio & site coverage
• Shadow length & overhang calculator