Where the sun is, checked against an ephemeris
· StorM Web Engine · 1 min read · BYTHECLOUD ENT
The StorM Web Engine computes the sun's direction for any moment and place and lights its world scenes from it. Its answers were compared with a published planetary ephemeris and with the official times of equinoxes and solstices.
The result
11.8″
Largest difference in sun direction, over every sample
383
Moments and places compared
2.6″
Median difference against the ephemeris
Source: Sun direction against published references · measured October 14, 2026
A sun drawn in the wrong place moves every shadow with it. Light through a window lands on the wrong wall, and a facade faces the evening sun at noon. The engine therefore computes the sun from the date, the time and the place, and the result is checked against answers that come from outside the engine.
Across 383 moments and places, the largest difference between the engine's sun and the reference was 11.8″ (0.0033°). That is the geometric direction behind what a scene uses: the sun's position in the sky and its conversion to compass bearing and height for one place on the ground.
Three references
Against a published, numerically integrated planetary ephemeris, at 240 moments spread over a decade, the sun's position seen from the centre of the Earth differed by 2.6″ at the median and 9.3″ at most.
From 96 moments at eight cities, using the same ephemeris for the bearing and height an observer on the ground would see, the largest difference was 11.8″.
At the official times of the 44 equinoxes and solstices of the same decade, the engine's sun stood within 7.2″ of the exact longitude that defines each one. The official times are given to the minute, so these figures include up to a minute of the sun's own motion.
What this covers
The figures are the worst of fixed samples, not a bound for every moment. The compared direction is the geometric one, without atmospheric refraction. Scene lighting adds the standard refraction near the horizon; that correction was not part of this check. The moon is not part of this check.