The boundary between daylight and darkness never stops moving. Follow it across the Earth, compare local times, switch on time-zone lines and twilight, and open the city stories to see how differently people have tried to organise the same sun.

The line between day and night is worked out live from the sun’s actual position; it’s not a pre-recorded dataset. Every time you open the exhibit, it calculates the sun’s declination for today’s date and its longitude for the current moment, then solves for every point on Earth where the sun sits exactly on the horizon. The formula behind this is a standard solar approximation, accurate to within a fraction of a degree. That’s plenty for a map at this scale, though nowhere near what a professional ephemeris would give you.

The twilight band shows civil twilight: the zone where the sun is between 0 and 6 degrees below the horizon. That’s the definition astronomers and meteorologists use.

City positions are approximate centre points, picked to spread across longitude and hemisphere so the day/night sweep reads clearly on the map. They’re not weighted by population.

Time zone names, offsets and daylight saving status pull from the same database your browser runs on. That means they update themselves and always show whatever offset is actually in effect right now. Nothing here is a fixed label that can go stale.

The short city histories are drawn from published sources, mostly museum and observatory records, national archives, and historical accounts, rather than original research. Where an account is disputed, or resting heavily on one source, the text flags that instead of presenting it as settled.