Earth rotation
The sky appears to rotate about 15° per sidereal hour because Earth rotates. Trails therefore curve around the celestial pole rather than moving as identical straight lines everywhere.
Star Trails: Rotation, Stacking and Gaps
See how total shooting time becomes angular trail length, and how frame gaps reduce stacking continuity.
Interactive trail simulator
Sky rotation—
Frames—
Capture duty—
Physical fact
The sky turns about 15° per sidereal hour because Earth rotates. Trail geometry is circular around the celestial pole; the pole altitude approximately matches your latitude.
Starting point
Try 30–90 minutes total, 15–30 s frames, and the smallest reliable interval gap. Check highlights and battery before committing to a long sequence.
Field check
Confirm the pole direction, foreground focus, intervalometer cadence and whether long-exposure noise reduction would create unwanted gaps.
Try it
Move latitude from 15° to 60° and watch the pole move. Then increase total time from 20 to 120 minutes and compare arc length.
Related
Why star trails have their shape
Declination
A star near the pole traces a small circle; one near the celestial equator covers a much larger angular path. Image trail length also depends on focal length and projection.
Stacking
Many shorter frames let you reject bad frames and protect highlights, but gaps between frames become breaks in the trail. Interval overhead matters almost as much as exposure duration.
Field workflow
Choose a pole-centered or directional composition first, estimate the total arc you want, then select frame length and interval. Avoid long-exposure processing that creates large gaps when continuous trails are the goal.