Sundial Simulator
An interactive horizontal sundial viewed from above. Set the latitude, date, and time to see how the gnomon’s shadow traces across the hour lines. The shadow moves faster near noon and slower near dawn and dusk. At extreme latitudes, observe midnight sun and polar night behavior.
How a sundial works
A horizontal sundial uses a gnomon (the vertical stick) tilted to the latitude angle, casting a shadow onto a dial plate. The hour line angles follow the formula: tan(H) = sin(latitude) × tan(hour_angle), where the hour angle is 15° per hour from solar noon. This means hour lines are not evenly spaced — they bunch up near 6 AM and 6 PM.
The equation of time
Solar time and clock time differ throughout the year because Earth’s orbit is elliptical and its axis is tilted. The “equation of time” correction ranges from about −14 to +16 minutes. This is why sundials and clocks disagree — and why the earliest sunset and latest sunrise don’t fall on the winter solstice.
Extreme latitudes
Above the Arctic Circle (66.5°N) or below the Antarctic Circle, the sun can stay above or below the horizon for 24 hours. During midnight sun, the shadow completes a full rotation. During polar night, there is no shadow at all.