Calculate polar alignment error in arcminutes and estimate tracking drift rate from your Polaris offset measurement.
Enter where your mount's polar axis actually points as right ascension and declination in degrees, plus the true pole coordinates — RA 0°, Dec 90° for the north celestial pole, or about RA 317°, Dec −89.3° for the south.
The angular separation between the two positions is computed with the haversine great-circle formula and reported in arcminutes. Pointing at Polaris itself, around 0.7° from the true pole, leaves an error of roughly 42 arcminutes.
Errors under 1 arcminute are marked acceptable for visual use. The drift estimate applies a rough rule of 15 arcminutes per hour for each degree of polar error — a heuristic for guidance only, since true drift also depends on declination and hour angle.
The calculator treats your mount's polar axis position and the true celestial pole as two points on the sky and computes their great-circle separation with the haversine formula, using right ascension and declination as spherical coordinates. The result appears in both arcminutes and degrees.
This tool marks errors under 1 arcminute as acceptable — a threshold suited to visual observing and short exposures. Long-exposure astrophotography is far less forgiving, and the drift estimate shows why even a fraction of a degree matters over an hour.
It applies a rough rule of 15 arcminutes of drift per hour for each degree of polar error, so a half-degree error suggests about 7.5 arcminutes per hour. It is a heuristic for ballpark guidance: actual drift also depends on declination and hour angle.
Yes — enter the south celestial pole as the reference, near RA 317° and Dec −89.3°, close to Sigma Octantis. Because there is no bright southern pole star, drift alignment or plate-solving is usually used to measure where the mount axis actually points.