Star trail photography turns the night sky into concentric arcs of light. As Earth rotates, stars trace circular paths around the celestial pole. Traditional photographers capture this with 20-minute exposures on a DSLR. With the right app, you can do it on an iPhone.

What You Need

A dark sky. Light pollution is the biggest obstacle. City glow washes out faint stars. Drive at least 30 minutes from any town, or use a light pollution map to find a dark spot near you. National parks, rural areas, and elevated locations work best.

A clear night with no moon. Clouds block stars. Moonlight brightens the sky and reduces star visibility. Aim for nights within a few days of a new moon. Weather apps with hourly cloud forecasts help you plan.

A tripod. Star trails require captures of 15 minutes or longer. No handheld technique can hold still that long. A small phone tripod (under $20) is enough.

A long exposure app. The iPhone's built-in camera cannot do star trails. You need an app that captures continuously and blends frames using lighten mode.

Camera Settings

Mode: Light Trail (lighten blending). This keeps the brightest pixel from each frame, so star positions accumulate into trails over time.

ISO: Start at 800. If stars are faint, push to 1600. Higher ISO means more noise, but stars need the sensitivity. Modern iPhone sensors handle ISO 1600 reasonably well.

Focus: Switch to manual. Autofocus cannot lock onto stars. Set focus to infinity, or focus on a distant light (a cell tower, a farmhouse on the horizon) and lock it before pointing at the sky.

Duration: Minimum 15 minutes for visible arcs. 30 minutes for clear trails. 60+ minutes for dramatic full arcs. The longer you capture, the longer the trails.

Step by Step

  1. Arrive early. Set up while there is still some twilight so you can frame your shot and find focus. Include a foreground element (a tree, a rock, a building) to anchor the composition.
  2. Point toward Polaris (North Star) if you want concentric circular trails. Point east or west for longer diagonal streaks. Point south for arcs that curve the opposite direction.
  3. Set your phone on the tripod and angle it toward your chosen area of sky. Lock the tripod tight.
  4. Open Lento, select Light Trail mode. Set ISO to 800-1600. Switch focus to manual and set to infinity.
  5. Use the self-timer (3 seconds) to avoid shake from tapping the shutter.
  6. Start capture and walk away. Do not touch the phone. Any vibration shows up as wiggles in the trails. Set a timer on your watch for your target duration.
  7. Stop capture when your timer goes off. Check the preview. If trails are too short, capture again for longer.
  8. Export as DNG for maximum editing flexibility. Star trail images benefit from contrast and color adjustments in post.

Common Problems

No stars visible in preview? Your location is too bright, or ISO is too low. Try a darker spot or increase ISO to 1600.

Trails are dotted, not continuous? This happens if the app drops frames or there are gaps between captures. Lento captures at 30fps continuously, so trails should be smooth. If they are still dotted, your exposure per frame may be too short for the star brightness.

Foreground is pitch black? Stars are faint, so the foreground gets almost no light. Two options: capture during blue hour (just after sunset) so the sky still has some light, or briefly shine a flashlight on the foreground during capture (light painting).

Airplane trails? Planes show up as bright straight lines cutting across the star arcs. There is no way to avoid them in a single capture. Shorter individual sessions with breaks can help you discard frames with planes, but the simplest approach is to accept them as part of the shot.

Best Seasons and Times

Star trails work year-round since they only require visible stars, not the Milky Way. But the best conditions are:

  • Winter: Longer nights, clearer skies in many regions, and bright winter constellations (Orion, Sirius).
  • New moon periods: Check a moon phase calendar. The darkest nights give the most visible star trails.
  • After midnight: Most artificial light sources (buildings, streetlights) dim after midnight. The sky gets progressively darker.

What Makes iPhone Star Trails Different

On a DSLR, star trails are captured as a single 20-minute exposure or hundreds of 30-second frames merged in software later. Both require significant post-processing.

On iPhone with frame stacking, the blend happens in real-time. You see the trails building on screen as they form. When the image looks right, you stop and export. No stacking software, no post-processing pipeline. The trade-off is smaller sensor and more noise, but for sharing on social media or printing at moderate sizes, the results are compelling.