Turn photos you already have into star trails

On the home screen, tap "Stack Images". Your gallery opens.

You can also select photos in your Photos app, tap Share and choose Trailium.

Tap every photo of the night sequence, then confirm. You can pick hundreds at once.

All photos should come from the same camera position. Moving the camera between shots breaks the trails.

Trailium brightens the stars, cleans the sky and removes noise from every frame. You see the progress at the top.

You can leave this screen while it works. It keeps going in the background.

Under "What would you like to create?" tap "Star Trails Image".

Open "Options" to choose the quality. 80% and 90% are free; 100% unlocks with a short ad.

"Comet Mode" fades the end of each trail so the stars look like they are streaking. "Reverse" flips the direction of the fade.

Tap "Create Star Trails Image".

Trailium is free. Some creations ask you to watch a short ad first, and your image starts processing while the ad plays, so no time is lost. You can skip ads with a Photon credit.

When it is done you get a notification. The image is saved in the Trailium album in your gallery.

Tap "Share result" to send it anywhere, or tap the info button to see how many frames went in and the total exposure.