Sunlight and shade

Seasonal Sun paths#

Compare the chosen day with both solstices.

A plan of the sky seen from above, like a site plan: north at the top, east on the right, south at the bottom, west on the left. The outer circle is the horizon and the centre is the point straight overhead (the zenith, marked +). The dashed rings are 30° and 60° above the horizon; their labels sit on the side away from the equator, where the paths rarely pass.

Each curve is the Sun's track across one day: it enters the circle where the Sun rises and leaves it where it sets. The closer a curve comes to the centre, the higher the Sun climbs. Ticks around the rim mark every 10° of compass direction, longer ones every 30°.

Today's path is drawn when the screen opens; the solstices frame it, so you can see at a glance where the Sun can and cannot reach during the year.

Under the diagram: sunrise and sunset with their compass direction, and solar noon, when the Sun is highest, with its height. The sentence above the diagram sums up the chosen time: the Sun's height and direction and the shadow of an object of the height you set.

Sun and shadow at selected time#

Object height, shadow length and bearing.

For the chosen date and time: the Sun's elevation (degrees above the horizon) and compass direction, and the shadow of a vertical object of the height you set with the − and + buttons (1 to 300 m; it is remembered).

Shadow length = height ÷ tan(elevation). The shadow points directly away from the Sun. Shadow per metre of height is the same ratio for any object: multiply it by a height to get that object's shadow.

The side view shows the object (white), its shadow on the ground (dark) and the sun ray grazing the top (dashed gold) with the Sun's angle. When the shadow is too long to draw, it is cut with a break mark.

Sun path#

Sunrise, noon, sunset and the daily path.

Sunrise and sunset with the direction the Sun appears and disappears, solar noon with the Sun's highest elevation, the length of daylight, and the shortest shadow of the day for your object height (at solar noon). Times assume a flat horizon; hills delay sunrise and bring sunset forward. Near the poles the Sun may not rise or set at all; the section then says so.

Solstices at noon#

The highest Sun in June and December.

The Sun's noon height and the noon shadow of your object on the two solstices of the chosen year: the highest and lowest the Sun gets at noon, and the shortest and longest noon shadows a design has to handle. The coloured line next to each matches its path on the diagram.

Solar energy#

Surface energy estimates and panel yield.

Long-term average sunshine energy from PVGIS (the European Commission's Photovoltaic Geographical Information System), based on satellite measurements over many years and including shading by surrounding hills and mountains. Nearby buildings and trees are not included.

"Facing south" or "facing north" is always toward the equator: south in the northern hemisphere, north in the southern.

Terrain horizon#

The surrounding hills and their effect on sunlight.

The skyline of hills and mountains around you, unrolled from north through east, south and west back to north; the height scale is in degrees above the horizon, with the top value labelled. The dashed gold lines mark today's sunrise and sunset directions, and the two facts give the terrain's height there: the Sun has to climb above it before it shines on you.

Shade from nearby buildings#

Model a neighbouring building’s shadow.

Enter a neighbouring building’s height and width, its true bearing and the distance from your observation point to the centre of its near face. The model treats that face as a rectangle perpendicular to its bearing, with a shared level ground datum. Observation height is the height of the point where you want to assess sunlight, for example a window centre.

The north-up plan draws the building face and its angular footprint to scale. A solid gold ray means the Sun clears the modelled building; a dashed orange ray means that building intercepts it. The skyline angle describes the building’s centre, while the blocking calculation also accounts for the ray’s offset across the face. A building lower than your observation point cannot block an above-horizon Sun.

The dimensions are your site inputs, not a building survey downloaded by iCaelum. This model covers one rectangular building face, not a whole neighbourhood, slopes or overhangs. The daily shade total excludes night and, when enabled, terrain-blocked periods.

Sunlight hours on each façade#

Compare the exposure of building faces.

Four full-day strips show potential direct sunlight at vertical north, east, south and west façade points. Gold means the Sun is above the horizon, in front of the wall and clear of the enabled obstacles. The custom outward bearing slider lets you inspect any wall orientation and lists its direct-sun windows.

The observation height and neighbouring building come from the preceding card. Each façade is evaluated at the same observation point; the model does not infer a building footprint or different window positions. Enable or disable the building and PVGIS terrain independently to compare their effects. If terrain is unavailable, the calculation explicitly uses a flat horizon.

Exposure uses five-minute midpoint samples across the actual local day, including 23- and 25-hour daylight-saving days. Window boundaries are approximate to five minutes. Incidence is the angle between the Sun ray and the façade’s outward normal; it is geometric and unobstructed, with no value when the Sun is behind the wall. These are potential sunlight hours, not a weather forecast, heat gain or electricity estimate.

3D sun path over the year#

Rotate and compare seasonal paths.

An orthographic 3D projection of the sky dome shows twelve calculated paths, one for the 21st of every month in your selected year. Rotate the camera and change its elevation to compare morning and evening bearings, seasonal noon heights and low winter paths. The ground ellipse and N, E, S and W labels establish geographic orientation; dashed dome rings mark 30° and 60° altitude.

Choose a month to highlight its curve in gold and inspect the reference date and highest sampled Sun. The white marker uses the main date and time controls, so it can fall between monthly paths. Paths and the marker are hidden below the geometric horizon; polar night and midnight sun receive explicit messages. These curves describe celestial geometry and are not clipped by the building or terrain models.