Star Trail Length Calculator
Calculate star trail lengths for long exposure astrophotography. Plan compositions and understand how Earth's rotation creates beautiful circular star trails.
Photography Parameters
hours
minutes
seconds
Total duration of star trail exposure
Lens focal length
Physical width of camera sensor
Physical height of camera sensor
Image resolution width in pixels
Declination of star you're tracking (-90° to +90°)
Star Trail Results
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Star Trail Visualization
Star Trail Photography Guide
Understanding Star Trails
Star trails are created by Earth's rotation during long exposures. The length and shape depend on:
- Exposure time: Longer exposures create longer trails
- Declination: Stars near celestial poles create shorter arcs
- Direction: Stars at celestial equator move fastest
- Focal length: Longer lenses magnify trail length
Trail Patterns by Direction
North Pole (Polaris)
Concentric circles around Polaris. Shortest trails near pole.
Declination: +89.3°
Celestial Equator
Straight lines across sky. Longest trails.
Declination: 0°
South Pole
Concentric circles around south celestial pole.
Declination: -90°
45° Declination
Curved arcs between straight and circular patterns.
Declination: ±45°
Star Trail Techniques
Single Long Exposure
- Pros: Simple, smooth trails, no gaps
- Cons: High noise, potential for ruined shots
- Best for: 30 minutes to 2 hours
- Settings: f/2.8-f/4, ISO 200-800
Image Stacking Method
- Pros: Lower noise, can recover from mistakes
- Cons: Possible gaps, complex processing
- Best for: 1-8 hour total duration
- Settings: 2-4 minute individual exposures
Planning Considerations
- Use PhotoPills or similar apps to plan compositions
- Scout locations during daylight
- Check weather and moon phase
- Bring extra batteries (cold weather drains them faster)
- Use intervalometer for precise timing
Recommended Exposure Times
| Trail Effect | Duration | Degrees of Rotation | Best For |
|---|---|---|---|
| Short Arcs | 15-30 minutes | 3.75°-7.5° | Foreground focus with subtle trails |
| Medium Arcs | 1-2 hours | 15°-30° | Balanced composition |
| Long Arcs | 3-4 hours | 45°-60° | Dramatic curved trails |
| Quarter Circles | 6 hours | 90° | Classic quarter-circle composition |
| Semi-Circles | 12 hours | 180° | Sunset to sunrise captures |
| Full Circles | 24 hours | 360° | Ultimate star trail challenge |
