Everything Star Trail Stacker can do
Six stacking modes, and every way to review, repair, blend and export the night you stacked.
Nothing is uploaded; the frames are read in your browser.
15 features · Filters need JavaScript
Star trails
Bring faint trails out of a changing sky
Each frame’s sky background is evened out before stacking, helping faint trails survive a changing sky.
How it works & the evidence
A plain lighten stack lets the brightest sky of the night decide what survives; here each frame's own background is taken out before the frames are combined. Click any pixel of a finished trail and it names the frame that made it.
Drag or use the arrow keys. See the full frames: before · after.
Star trails
Close the gaps between frames
The pause between exposures leaves gaps in every trail; they are closed along each star’s own arc, using light the camera recorded.
How it works & the evidence
Exposure and interval from your frames guide the repair, and you set how much of each gap is filled.
Drag or use the arrow keys. See the full frames: before · after.
Star trails · Nightscape
Keep the trails. Remove passing lines.
Find aircraft and satellite lines before stacking, and review the proposed repairs.
Stack a night with line removal
How it works & the evidence
Neighbouring frames are compared before anything is stacked, each proposed line is measured again on the full-resolution original, and what is replaced comes from observed neighbouring sky. In a credited Yebes Observatory test night, every one of the 3,273 masked samples matched an observed donor exactly.
Nightscape
Stack the sky. Keep the ground sharp.
Keep one reference frame for the foreground, then refine the boundary that joins it to the stacked sky.
How it works & the evidence
Nothing here can register, warp or reconstruct a foreground.
Deep sky
Align your deep-sky frames
Align Lights to a reference, combine them, and export a picture or a 32-bit FITS for further editing.
How it works & the evidence
Lights are registered against a reference you choose, integrated by mean, exact median or sigma-clipped mean, and written as a signed, unclamped 32-bit FITS as well as a picture. Sigma clipping refuses fewer than eight Lights before a single file is decoded.
Comet
Follow the comet and the stars
Mark the nucleus in each frame to create separate star and comet stacks, plus a combined image.
How it works & the evidence
You mark the nucleus on every frame; out come a star-registered stack, a comet-registered stack and the composite on one exact grid. Nothing about a nucleus is ever guessed for you.
Planetary
Choose the sharpest moments
Score a SER, a supported AVI, or an MP4/MOV with one H.264 or HEVC track, then stack the best frames from your chosen region.
How it works & the evidence
One SER capture, one of the named AVI subsets, or one MP4/MOV with an H.264 or HEVC track is validated before a single frame is read, scored frame by frame, and the best of it is stacked. Choose a reference frame, a region and how many of the best frames to keep.
Calibration lab
Build your reusable calibration masters
Darks, flats, bias and dark-flats become reusable master FITS, built in your browser.
How it works & the evidence
Frames are sorted into compatibility groups deterministically and loaded one at a time, so a session needs the memory of one frame rather than of all of them.
Every mode
Start with your camera’s files
Choose JPEG, PNG, WebP, TIFF, camera RAW, FITS or SER in the modes that support them.
How it works & the evidence
Photo modes take JPEG, PNG, WebP and TIFF; camera RAW, FITS and SER are read in the modes that support them, and the format page lists what has actually been through it. Your photographs never leave your device: this static site has no image-upload endpoint, and processing happens inside your browser.
After the stack: review, finish and keep a night
Star trails · Nightscape
Review every line. Keep the meteor.
Each proposed line can be checked in its original frame, then set to Keep or Remove before you stack again.
How it works & the evidence
It finds straight lines; you choose what stays, so a meteor can stay.
Star trails
Remove a line the detector missed
Draw along a line on the finished picture, check it, and apply the removal; several lines can be applied together.
How it works & the evidence
When the previous run was kept, the picture updates without running the night again; otherwise the night runs again with your marks.
Star trails
Eight blends, including Javelin
Choose equalised lighten, plain lighten, darken, average, additive, multiply, subtract or Javelin, which tapers both ends of every trail.
How it works & the evidence
Equalised lighten is the recommended default: each frame’s sky is evened out before the brightest value at each pixel is kept.
Star trails
Turn the night into a time-lapse
Tick one box before Start and the run also writes an MP4: the trails building up, the night as it was shot, or both.
How it works & the evidence
Choose the frame rate and a shape for YouTube, Reels or a feed post, then make cover images for the post from the same run.
Every mode
Files your editor can open
Save a 16‑bit PNG, or an uncompressed 16‑bit TIFF in Star trails and Nightscape.
How it works & the evidence
Deep sky also writes a signed, unclamped 32-bit FITS for further editing, and the Calibration lab writes its masters as FITS.
Every mode
Save a night and come back to it
The Library keeps named nights in this browser: their settings, masks and frame decisions, never the photographs.
How it works & the evidence
Continue a night where you left it, or repeat its settings on a new set of frames; nothing starts until you press Start.
How it compares with a plain lighten stack
What a star-trail stacker should do, and most miss sets this tool beside a plain lighten stack, line by line, with the measurement behind each difference. Measured beside a desktop star-trail app runs it against a paid desktop stacker on one laptop, including where this tool was slower.