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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

Δt=4 Δλ\Delta t = 4\,\Delta\lambda
sig figs

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. Change any unit and the answer follows.

Constant used: built into this formula, no need to enter
180π=57.29577951308232 ∘/rad\frac{180}{\pi} = 57.29577951308232\ ^{\circ}\text{/rad}Degrees per Radian · exact

See also

Solar Declination Angle (Cooper's Equation): The other half of where-the-sun-is: how far north or south it stands through the year.
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Longitude to Solar Time Difference explained

ΔλΔt

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.

Longitude to Solar Time Difference formula

Δt=4 Δλ\Delta t = 4\,\Delta\lambda
Where
  • Δt\Delta t= Solar time difference (min)
  • Δλ\Delta\lambda= Longitude difference (°)
Revised 16 October 2026
Cite this page

formula.expert. (2026, October 16). Longitude to Solar Time Difference Formula & Calculator. https://formula.expert/solvers/longitude-time-offset

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