Understanding and calculating the sun path

1Why the sun's arc changes through the year

The Earth's axis is tilted by 23.44° against the plane of its orbit. At the June solstice around June 21 the sun therefore stands 23.44° north of the celestial equator, at the December solstice around December 21 just as far south, and at the March and September equinoxes right on it. This angle is called the declination.

That gives a rule of thumb for noon in the northern hemisphere: sun altitude = 90° − latitude + declination. At 50° latitude that is 90 − 50 + 23.4 ≈ 63° in June, 40° at the equinoxes and just under 17° in December.

The direction of sunrise and sunset moves with the declination. At the equinoxes the sun rises almost exactly in the east (azimuth 90°) and sets in the west (270°). In London it rises on June 21 at 49° in the north-east and on December 21 at 128° in the south-east. The further from the equator, the wider the swing.

2Reading the chart and the map in SunPosition

The chart in the “Path” tab plots compass direction horizontally and the sun's altitude vertically. It shows three arcs: the sun path of the selected day with hour marks, above it the path of June 21 and below it that of December 21. Every other day of the year lies in between. The dot on the day's arc is the sun at the selected time.

The map shows the same from above: lines from your location towards sunrise (yellow), sunset (red) and the sun at the chosen moment (orange), plus the shadow direction. The dotted arc is the day's path – the direction from the location is the azimuth, the distance from the centre the altitude: on the grey circle the sun is at the horizon, towards the centre it climbs higher.

This is how you read off shading: anything that, seen from your spot, rises higher than the winter path takes the sun away from it in December. If a building to the south rises 15° above the horizon as seen from your window, it blocks the noon sun in Edinburgh in December (10.6°) – but not in June (57.5°).

3Noon altitude and day length for five cities

The table gives the sun's altitude at its highest point and the day length on the two solstices of 2026, computed with SunPosition. Day length runs from sunrise to sunset of the sun's centre at 0.833° below the horizon – the convention used by NOAA and the almanacs.

Sydney lies in the southern hemisphere: there June is winter, and at noon the sun stands in the north. Latitude decides the rest – Edinburgh, four degrees north of London, has almost an hour more daylight in June and nearly an hour less in December.

4Sunrise and sunset: time and direction

Time and compass direction of sunrise and sunset on the two solstices of 2026, in local time (daylight saving time where it applies). The angle is the azimuth, counted clockwise from north.

5Solar noon, time zones and daylight saving time

The sun is highest when it stands due south (in the southern hemisphere due north) – at solar noon. That hardly ever happens at 12:00 on the clock. A time zone is laid out for one meridian; for every degree of longitude west of it, noon comes four minutes later.

On top of that comes the equation of time: because the Earth's orbit is elliptical and its axis tilted, a sundial runs up to 16 minutes fast and 14 minutes slow over the year. London lies almost on the Greenwich meridian, so its solar noon falls at 11:59 GMT on December 21 and at 13:02 British Summer Time on June 21, that is 12:02 GMT.

SunPosition shows all times in the time zone of the selected location, not that of your device – plan a place in Portugal from Germany and you see Portuguese time.

6Patio, buying a home, solar panels: putting the path to use

Patio and balcony: set the day you want to sit outside – an evening in May, say – and move the time slider. The map shows where the sun comes from and when it disappears behind the house next door.

Buying a home or a plot: check December 21. If, seen from the living-room window, the winter path runs above the roofs opposite, the room gets sun in winter too. The camera view shows this on site, right in the image.

Solar panels: spring, summer and autumn count most for yield. Anything to the south, south-east or south-west of the roof that rises above the paths of those months costs yield. How much a system on your roof produces is what the sister app SolarFinder calculates.