Star trails without the airplanes.

Every mode, in detail

• Star trails — and the aircraft search measured against somebody else's labels
• Nightscape — two products, and the foreground it will not invent
• Deep sky — three methods, and the eight-frame refusal
• Comet — where every scientific decision is yours
• Planetary — the header it reads first, and the three choices it insists on
• Calibration lab — the groups it will not mix

Tells you what to shoot before it tells you what it did

The gap between exposures is what ruins a star trail, not the exposure, and in-camera noise reduction is the usual culprit. The whole job, from the night to the finished file, is five steps. Your first star trail.

Says which file types a real file has been through, and which only a fixture

Code that accepts an extension is not the same as a file of that kind having been read, and the gap between the two is where people lose an evening. Every format carries which of the two is true — including the five RAW containers nothing has ever been read from. What it can read.

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

So the gap-fill radius is computed, not guessed. Most tools 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. Warm pixels in RAW frames, bright in only some of them, are found in each frame's sensor mosaic and taken out of the finished stack before gap filling, which would otherwise draw each one out into a coloured dash.

Finds natural satellite trails; aircraft stay reviewable and measured

On five independently labelled crops from the licensed ASTA MeerLICHT corpus, it found all six satellite trails — thin, saturated, parallel and crossing — and none in the clean crop. The protective masks recovered 97.2–100% of labelled trail pixels; their 21.6–49.8% pixel precision is intentionally lower because the mask extends beyond the bright core. This small tracked-telescope benchmark validates detection and mask geometry, not the later star-arc repair. On two paths in a credited consecutive Yebes Observatory sequence, ordinary detection found 3/5 and 2/3 positions; sequence evidence rebuilt the first to 4/5 automatically and offered the missing position in the second as review-only, reaching 3/3 after an explicit Remove decision. Exact leave-one-Light-out checks matched all 3,273 and 5,376 masked RGB donor samples. This is still a small corpus: current blind spots include short tracks and one weak, sparsely dashed endpoint that remains missed. See what a removal actually changes, on one of those frames.

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.