Polar Alignment Calculator — Equatorial Mount Setup

An equatorial mount must be aligned with the Earth's rotational axis to track stars accurately. Poor alignment causes field rotation and star trailing, especially with longer focal lengths and longer exposures. Even 1 arcminute of error can produce visible trailing in multi-minute exposures.

Point the mount's polar axis towards Polaris (the North Star), then use a polar scope or electronic alignment tool to fine-tune. Polaris is offset about 0.65° from the true celestial pole, so simply pointing at Polaris is not precise enough for long-exposure astrophotography.

It depends on how much declination drift you can tolerate over a sub-exposure. Because a 1-arcminute error drifts a star by about 0.262 arcsec per minute, wide-field setups (14-35mm) with 30-60 second subs cope with roughly ±5 arcminutes, moderate focal lengths (100-300mm) want ±2-4 arcminutes, and long focal lengths (500mm+) or multi-minute subs need sub-arcminute accuracy to keep stars round.

Yes. You can use drift alignment (observe a star near the meridian and celestial equator, then adjust until drift is eliminated) or electronic polar alignment tools like SharpCap or NINA, which plate-solve to determine your exact alignment error.