Star trails from a night of exposures, in this tab

Drop the folder in. It reads your frames, tells you what kind of night you actually had, and builds the stack while you watch. Every stacker takes the brightest value at each pixel; this one equalises each frame's sky background first, which keeps the faint trails a plain stack loses — most on the nights your sky moved most, and the tool measures yours and says which kind of night it was. Nothing is uploaded: there is no upload endpoint here to send it to.

What it does before you touch a control

Reads the interval, the exposure and the image scale out of your files

So the gap-fill radius is computed, not guessed. StarStaX and the browser tools both ship it as a slider with no units; it is arithmetic, and the page shows you the arithmetic. Why trails come out dotted.

Measures how far your sky drifted, and says so in your own units

A night whose background moved twenty-five times its own noise is a night where a plain lighten stack keeps almost nothing; a steady four-sigma night is one where the difference is modest and you should be told that too. It is a fact about your sequence, and you get it before the download, not after.

Equalises each frame's background before the blend

The whole difference — and how much it is worth depends on your night, not on this page. Measured on three cameras, with the range and its limits.

Leaves out the frames that would spoil it, before they are in

Cloud and passing headlights raise a frame's whole background; those frames are found and set aside first, because a maximum cannot be undone once it is taken.

Removes stuck sensor pixels, and does not touch your foreground

A pixel bright in nearly every frame is a sensor defect that max turns into a permanent fake star. A whole treeline is also bright in every frame — so only small, isolated clusters are repaired.

Looks for aircraft trails, and says what it cannot see

It looks — it has never been shown a real aeroplane on real camera files, because no dataset anyone can license contains one, so it does not claim to remove them. What it looks for is a streak in a single exposure that is longer than three star trails, no wider than your own stars, and not lying along the star arc. Two things get past it and it tells you so on your own pictures: a streak shorter than the search can resolve, and a long trail made of widely spaced anti-collision flashes.

Nothing is removed that cannot be repaired afterwards

A star sits on any given pixel in exactly one frame, so masking that frame deletes the star from the result — on real tracked stars, masking one frame of thirty-eight took 22.8 of a 25.9 sigma peak away. The hole is closed again along the star's own arc, and a trail is only ever masked where that repair can reach. If it cannot reach, the trail is reported and left alone.

What it does not do

It has no automatic sky mask and does not stack a foreground separately, no comet mode, no video export. Sequator does several of those and does them well — it is Windows-only, and that is the honest reason this exists rather than any claim to be cleverer. What runs on a Mac, compared fairly.

Three kinds of RAW it will not read, and it says which and why rather than calling your file unsupported: Nikon High Efficiency NEFs, whose pixels are behind a licensed codec; linear DNGs from Samsung Expert RAW and Apple ProRAW, which the phone already demosaiced; and Fujifilm GFX medium format, which is too much for a tab. The decoder, and the source we publish for it.

It is free, it has no account, no advertising and no payment, and it is not going to ask you for an email address. Why.