Why is polar alignment important?

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.

How do I polar align in the northern hemisphere?

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.

What alignment accuracy do I need?

For wide-field (14-35mm) with 30-60 second subs, ±5 arcminutes is usually acceptable. For moderate focal lengths (100-300mm), aim for ±1-2 arcminutes. For long focal lengths (500mm+) or very long exposures, you may need sub-arcminute accuracy.

Can I polar align without seeing Polaris?

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.

Polar Alignment Calculator — Equatorial Mount Setup

Calculate polar alignment requirements and tolerances for your equatorial tracking mount.

Observer Latitude

Your geographic latitude (e.g. 52 for London)

Focal Length

Imaging focal length

Exposure Time

Sub-exposure duration

How We Calculate This

The celestial pole altitude equals your geographic latitude. In the northern hemisphere, Polaris is offset approximately 0.65° from the true North Celestial Pole.

Pole altitude = observer latitude

The alignment tolerance depends on your focal length and exposure duration. Longer focal lengths and longer exposures require more precise alignment. Star trailing due to alignment error accumulates at approximately 15 arcseconds per second of time per degree of misalignment.

Trail (arcsec) = alignment error (deg) × exposure (s) × 15 arcsec/s × (1/60)

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.