How to manage satellite trails in astrophotography

A satellite can reflect sunlight as it crosses your field of view, leaving a streak in an exposure. Aircraft, meteors, tracking problems and reflections can also produce marks, so do not assume every line has the same cause. A satellite prediction may help identify a likely pass, but a match is not proof.

Keep the original files. Look at several neighbouring frames and check whether the line affects only a small area or is accompanied by a bright flare, haze, saturation or other problems. If the frame is otherwise useful, try it in a stack before deciding to discard it. If a flare overwhelms a large area, compare the result with that frame excluded.

The Rubin Observatory media kit explains that satellite reflections can leave streaks and affect astronomical observations. The impact on your image depends on the equipment, exposure and trail; there is no guaranteed clean result.

For a deep-sky target, take a series of suitable exposures with the same framing and camera settings, and keep the raw files. A sequence gives your stacking software other views of the same sky to compare when a trail appears in one frame. It also lets you leave out a poor frame without losing the whole session.

There is no single best exposure length. Shorter frames can limit how much time is represented by an individual affected frame, but camera read noise, sky brightness, tracking and the target also matter. Take a test, inspect the stars and highlights, and follow the advice for your own camera. For the capture workflow, see our first deep-sky setup guide.

For a wide landscape with a foreground, the land and moving stars need different alignment. A single nightscape exposure or a star-trail composite is a different editing problem; do not expect deep-sky stacking settings to work unchanged.

After calibration and star alignment, many stacking tools can compare each position across the registered images and mask unusually high or low values before combining them. A satellite trail present in only a few frames may be treated as an outlier. Astropy's image combination documentation explains sigma clipping and masking; the controls and names vary between programs.

1. Save your originals and calibrate and align the compatible light frames using your software's instructions.
2. Make a stack using its available rejection method. Inspect the result and, if available, its rejection map or statistics.
3. If a streak remains, check alignment and compare a stack with the worst frame excluded. Review the software's guidance before changing rejection thresholds.
4. Compare stars and faint structure as well as the line. Aggressive rejection can discard useful data; too little rejection can leave the trail visible.

A small number of frames, repeated trails in the same area, a bright flare or saturation can make rejection less effective. There is no universal minimum frame count or threshold that works for every data set. Siril's manual processing guide recommends checking the rejection result and adjusting settings when needed.

Dithering makes small shifts between exposures. It can help reduce fixed-pattern effects after the images are aligned, but it is not a guarantee that a satellite trail will disappear. Siril's FAQ explains its use for camera pattern noise. Use your capture software's instructions if your mount supports dithering; a simple fixed-camera session may not.

A satellite needs sunlight to be seen by reflected light. Twilight can be a more affected period, but visibility depends on orbit, location and season, and satellites can still be visible later. The IAU Centre for the Protection of the Dark and Quiet Sky describes these limits. Moving a session later may not suit the target, weather or your access arrangements and cannot guarantee a clear frame.

If only one frame is affected and you have others, compare the stack with and without it. With a very small stack, or when a bright trail crosses the same area in many frames, collecting more suitable data on another night may be more useful than forcing a setting.

For a single image, a local edit may hide a streak, but it cannot recover detail that was never recorded. Keep an untouched original and disclose substantial edits when sharing work as documentary or scientific evidence. For a full processing sequence, see how to process your first deep-sky image.

Sources reviewed 15 November 2026: Rubin Observatory, Astropy ccdproc, Siril and the IAU dark and quiet sky report.