AN INSTRUMENT FOR DAYLIGHT
Urban shadow
At the same clock time, one street can be in sun while another is in shade. Choose a place, move the day, and make daylight move at building level.
An approximate solar model for a level surface. The building height is a visual object, not a measurement of a real building.
ONE DATE, DIFFERENT DAYS
Day length changes with place.
On 21 June, six cities receive the same astronomical date in different shapes. Each bar shows the interval between sunrise and sunset in that city’s local time.
THE OBJECT EXPLAINS
A long shadow is a clock.
When the Sun is low, the building throws a long shadow. As the Sun climbs, the shadow tightens. The same façade keeps a trace of both the hour and the Sun’s height.
Choose a moment of the day. The building stays the same; only the Sun moves.
At solar noon, the shadow reaches its shortest length of the day.
Length is reported against a 24 m model building. It does not describe a particular building.
ONE CITY, ONE YEAR
Daylight has a curve.
Choose a month and watch day length change in the selected city. The line is calculated for every day of the year; the yellow point is the date in the scene.
HOW TO READ IT
A good approximation is still an approximation.
The calculation uses latitude, longitude, date, time zone, the equation of time, and solar declination. Sunrise and sunset include the standard correction for atmospheric refraction. Clouds, nearby buildings, terrain, and a real window’s orientation can change the light you actually see.
Method
The equations follow NOAA documentation for solar position and sunrise/sunset. City coordinates are calculation points, not a map of every neighbourhood.
Primary source
NOAA Global Monitoring Laboratory, Solar Calculator
NOAA calculation details
U.S. Naval Observatory, reference astronomical data
Status: evergreen, periodically reviewed. Results are educational and may differ from local observation.