How long do I need to expose for star trails?

For short arcs (15-30°), 30-60 minutes is sufficient. For full circle trails around the pole star, you need a full night (6-8 hours). Most impressive star trail images are 1-3 hours long, creating arcs of 15-45 degrees.

Should I use one long exposure or stack shorter ones?

Stacking multiple shorter exposures (typically 15-30 seconds each) is strongly recommended. It reduces noise, prevents overexposure from light pollution, allows you to remove frames affected by aircraft or clouds, and avoids the battery drain and sensor heating of very long single exposures.

Why leave a gap between exposures?

Most cameras need 1-3 seconds between shots for the shutter to reset and the image to write to the card. This gap creates small breaks in the trails, though these are usually invisible at normal viewing sizes. An intervalometer automates the timing.

Which direction should I point the camera?

For circular trails, point towards the celestial pole (Polaris in the northern hemisphere). For straight trails, point east or west along the celestial equator. For a mix of curved and straight trails, point roughly north-east or north-west.

Star Trail Calculator — Plan Your Star Trail Photography

Plan star trail photography sessions with exposure count, duration, arc length and storage estimates.

Mode

Single exposure or stacked shorter exposures

Total Duration

How long to shoot in total

Exposure per Frame

Duration of each sub-exposure

Gap Between Frames

Shutter reset / write time

Focal Length

For reference only

How We Calculate This

Star trails are caused by the Earth's rotation. The Earth completes one full rotation (360°) in approximately 23 hours 56 minutes (86,164 seconds — a sidereal day).

Arc length (degrees) = (total time in seconds / 86,164) × 360

For stacked exposures, the frame count is calculated from the total shooting time divided by the cycle time (exposure + gap). Storage estimates assume approximately 25 MB per RAW frame.

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.