Measure latitude with Polaris
Measure the North Star’s altitude from a level horizon. Compare it with latitude while accounting for Polaris’s offset from the celestial pole.
What you need
- Angle instrument with a level reference
- Location latitude and observation time
- Unobstructed northern sky
Collect the readings
- Calibrate the angle instrument against a horizontal reference. Sight Polaris and record the angle above that reference, not above a sloping roof or mountain ridge.
- Repeat the reading and swap the observer when possible. Record the date, UTC time and instrument uncertainty. Near the horizon, atmospheric refraction can be important.
- Enter latitude and the chosen Polaris declination in the calculator. Its range between lower and upper culmination shows why an arbitrary single Polaris reading need not equal latitude exactly.
- Compare with an independent location estimate. If the result falls outside the expected range, recheck the star identification, instrument zero and horizon datum before applying an unexplained correction.
Compare the predictions
The north celestial pole altitude equals latitude in spherical geometry.
Polaris circles that pole; use an epoch-appropriate declination for precision.
At southern latitudes, Polaris can stay below the geometric horizon.
Open the related calculation →