Skyfold Sun Position and Shadow Length

What it is for

Gardeners want to know where a new tree will throw its shade, architects check a neighbour's right to light, photographers look for long evening shadows, and teachers measure the Sun's height with a stick. This tool computes the Sun's position for a place and time and the length and direction of the shadow cast by a vertical object on level ground.

Besides the moment you choose, it lists the shadow through the whole day, the times of sunrise, solar noon, sunset and golden hour, and draws a plan of the shadow and a world map of day and night. It is the engine of the Sun & shadow and Day and night map tabs in the Skyfold app.

Worked example

The second example is a 30 ft house in Phoenix (33.4484, -112.074, America/Phoenix) at noon on 2026-12-21, the winter solstice. The summary reads: the Sun stands 32.79° high in the south; a 30 ft object casts a 46.57 ft shadow towards the north (353°).

The day table shows how the shadow shrinks and grows: 341.3 ft at 08:00 with the Sun at 5.02°, 69.6 ft at 10:00, the shortest at 12:30 with 45.96 ft, and 448.7 ft at 17:00 just before sunset. The day block gives sunrise 07:28, solar noon 12:27, sunset 17:25, a noon altitude of 33.11° and the evening golden hour from 16:47.

The first example, a 6 m tree in Munich at 16:00 on the March equinox, gives a 14.34 m shadow towards the north-east (62°) with the Sun at 22.71° in the south-west.

How to read the result

• Sun azimuth is measured from north through east; Sun altitude includes normal atmospheric refraction.
• Shadow length is height ÷ tan(altitude). Shadow direction points away from the Sun (azimuth + 180°).
• Length ÷ height lets you scale the answer to any other object: multiply its height by this factor.
• The shadow plan shows the scene from above with north up: the bold line is the shadow now, the dashed line the path of the shadow's tip through the day.
• The day-and-night map shades twilight bands and night, marks the point where the Sun is overhead and your place.

Tips and common mistakes

• Use the local time zone of the place; the tool shows the UTC offset in its outputs.
• Below about half a degree of Sun altitude the shadow is effectively endless, and after sunset there is none — the tool says so instead of giving a number.
• On sloping ground, real shadows are longer downhill and shorter uphill than on flat ground.
• Check the winter solstice for the longest midday shadows and the summer solstice for the shortest.
• A table step of 15 minutes is useful around sunrise and sunset, when the length changes quickly.

FAQ

How accurate is the Sun position?

The Sun's altitude and azimuth match the U.S. Naval Observatory's navigation data and the NREL solar position worked example to about 0.001°, far better than any shadow measurement.

Why is the shortest shadow not exactly at 12:00?

Because solar noon depends on your longitude within the time zone and on the equation of time. In Phoenix in December it falls at 12:27.

Does it account for buildings or terrain?

No. It assumes flat, level ground and a thin vertical object; neighbouring buildings, hills and the width of the object are not modelled.

Can I use feet?

Yes. Choose feet as the unit; the shadow lengths are then given in feet as well.