Online Tool Store
Star Trail Exposure Calculator
Star Trail Exposure Calculator shows the arc your framing will produce, and dashed trails are almost always the interval rather than the plan.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
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Star Trail Exposure Calculator
Frontend preview — no upload or external service.
Sequence plan
180 frames of 30 seconds gives a 90-minute trail. Near the celestial equator that is an arc of about 22 degrees; near Polaris the same time produces much shorter trails.
How the Star Trail Exposure Calculator works
- Set the total duration you want the trails to span, which determines the arc length.
- Choose a frame length short enough to avoid sensor heat and long enough to keep the file count manageable — 30 seconds is a common compromise.
- Minimise the interval between frames. Gaps produce dashed trails, which is the most common and most visible mistake.
The method
The sky rotates 15 degrees per hour, so trail length depends on total duration and on how far the target is from the celestial pole.
arc = 15 degrees per hour x duration x cos(declination)
Stars near Polaris trace tiny circles while those on the celestial equator sweep the full rate, which is why framing decides how dramatic the trails look.
FAQ
Why stack frames instead of one long exposure?
Because a single very long exposure accumulates sensor noise and heat, and any error — a passing car, a plane, a cloud — ruins the whole frame. Stacking lets you discard the bad ones.
Why are my trails dashed?
Gaps between frames. The camera needs to write each file, and if the interval exceeds that write time you get a visible break. Turn off long exposure noise reduction, which doubles each frame's time.
Which direction should I point?
Toward Polaris for concentric circles, or east or west for long sweeping arcs. Near the celestial pole the trails are short even over hours, which is a compositional choice rather than a limitation.
How we compare
| Feature | Online Tool Store | A desktop editor | An upload-based service |
|---|---|---|---|
| Arc length calculated | ✓ | ✗ | ✗ |
| Frame count planning | ✓ | ✓ | ✓ |
| No sign-up | ✓ | ✓ | ✗ |
| Nothing uploaded | ✓ | ✓ | ✗ |
Star Trail Exposure Calculator shows the arc your framing will produce, and dashed trails are almost always the interval rather than the plan.