Solar Azimuth Hour Angle Calculator
Determine the true azimuth of a survey line from a sun observation. The sun’s position is computed automatically from your date, time and location — no almanac lookup needed.
Field aid, not a certified result. Accurate to roughly ±0.01° under typical conditions, but always verify against known control where available.
Observation time (local)
Station position
Field observation
Fill in every field above to compute the true azimuth.
Amber = Sun · Line = line azimuth
Show calculation steps
| Day of year | – |
| Equation of time | – |
| Solar declination | – |
| Solar hour angle | – |
How solar azimuth observation works
Quick answer: The sun’s azimuth at any moment can be computed from its hour angle — how far it has moved from the local meridian — combined with its declination and your latitude. Subtracting a field-measured horizontal angle from the line to the sun then gives the true azimuth of the line, the same principle used in a Polaris observation but with the sun instead of a star.
The sun’s hour angle comes from true solar time, not clock time. Clock time runs at a constant rate and is tied to a time zone’s reference meridian, while the sun’s actual position drifts against that clock by up to about 16 minutes through the year — a discrepancy called the equation of time, caused by Earth’s elliptical orbit and axial tilt. Correcting clock time for the equation of time and for how far your longitude sits from your time zone’s reference meridian gives true solar time, from which the hour angle follows directly: 15° per hour away from solar noon.
Once hour angle, declination and latitude are known, the same spherical-astronomy formula used for star observations gives the sun’s azimuth. A solar observation is more forgiving on timing than a Polaris shot — because the sun moves faster across the sky in azimuth at most latitudes, a given timing error causes a smaller azimuth error than the same error would with Polaris — but it also requires care to avoid instrument damage and eye injury, always using a proper solar filter.
Sun vs. Polaris observations
| Solar observation | Polaris observation | |
|---|---|---|
| When | Daytime | Night, when visible |
| Coordinates needed | Computed from date/time automatically | Current almanac RA/Dec required |
| Timing sensitivity | Lower at most latitudes | High — corrections needed |
| Safety | Requires a proper solar filter | None beyond normal night work |
Frequently asked questions
What is the equation of time and why does it matter here?
It’s the difference between clock time and true solar time, which varies through the year by up to about 16 minutes due to Earth’s elliptical orbit and axial tilt. Skipping this correction would compute the sun’s position for the wrong moment.
Do I need to know the sun’s right ascension and declination?
No. Unlike a Polaris observation, this calculator derives the sun’s declination directly from the calendar date using standard solar position formulas, so there’s no almanac lookup required.
How accurate is this method?
The underlying solar position formulas are accurate to roughly ±0.01° for dates between 1950 and 2050, which is more than sufficient for practical azimuth work — your field angle measurement is typically the larger source of error.
Is it safe to sight the sun directly with a theodolite or total station?
Never sight the sun directly without a proper solar filter over the objective lens — it can cause permanent eye damage and instrument damage almost instantly. Use purpose-made solar observation filters designed for survey instruments.
Why does solar elevation matter for this calculation?
It’s mainly a sanity check — a negative elevation means the sun would be below the horizon at that date, time and location, which signals an input error rather than a usable observation.
Does this replace a licensed survey control check?
No. This is a field calculation aid. Always verify azimuth results against known control where available and follow the standards required for your jurisdiction and project.
