Longitude to Solar Time Difference
Also known as longitude to time · 4 minutes per degree · solar time from longitude · time difference between longitudes · finding longitude by chronometer
Worked example: 15 degrees of longitude → 60 min (one time zone) — press Try an example to run it live, then adjust anything.
Enter your known values, leave one input blank, and solves for the missing one. Tap a variable’s symbol to see what it means, with a typical value. Try different units for next level excitement!
Learning zone
The Earth turns 360° in 24 hours, which is 15° per hour, which is 4 minutes per degree — pick whichever form you can recall under pressure, they are the same fact. Stand one degree of longitude west of a friend and your sun runs 4 minutes behind theirs: solar noon, sunrise, sunset, all shifted together.
Two honest caveats. Civil time ignores this smoothly varying offset and snaps it to zone boundaries drawn by politics, so your WATCH can disagree with your sun by more than an hour (China runs one zone across four sun-hours of country). And the sun itself runs up to ±15 minutes off its own average through the year — the equation of time — which is why a sundial and a watch only agree four days a year. This formula gives the clean geometric part; navigation by chronometer was built on exactly it, run backwards: know Greenwich time, observe local noon, and the difference IS your longitude.
- = Solar time difference (min)
- = Longitude difference (°)
- Solar time difference — Dead Reckoning Position, Estimated Time En Route
- Longitude difference — Dead Reckoning Position, Initial Great Circle Bearing