Set up & understand Nocturne

Getting started

Nocturne turns a stacked smart-telescope image into a finished picture through a guided, non-destructive flow. Nothing you do is permanent until you export, so you can experiment freely — undo, redo, or jump back to any step.

1. Install the app

Download Nocturne for macOS and drag it to Applications. Nocturne currently runs on Apple Silicon Macs (M1 or newer) only — there's no Intel build yet. It isn't notarized either, so on first launch macOS may block it — right-click the app → Open → Open, or allow it under System Settings → Privacy & Security. You only do this once.

2. Open a stack

Choose Open FITS and pick a stacked master (.fit / .fits). Don't have a stack yet? Use Stack to point Nocturne at a folder of raw subs — it grades out the bad frames, aligns the rest (handling the field rotation from an alt-az mount), and integrates a clean master for you. If your subs cover several pointings, tick Mosaic and it stacks each panel, plate-solves them and assembles one wide image. That one needs ASTAP installed, and takes considerably longer.

No data of your own yet? Download a sample set — real Seestar captures, free to use, ready to open.

3. Work down the steps

Each step offers simple choices (often just Light / Medium / Strong) with a live before/after. The panel explains what the step does; once you know it, collapse the help with “How this works” and it stays out of the way. When you're happy, move on with Next.

How the pipeline works

A quick tour of the steps, in the order Nocturne walks you through them. You can skip any you don't need.

Prepare — Stack, Crop, Background

Stack builds a master from raw subs (or you open one directly). Crop trims stacking artefacts at the edges, with composition guides. Background (GraXpert) removes gradients and light-pollution glow so the sky is even and neutral — tick Show what was removed afterwards to see the gradient on its own and confirm it took sky-glow rather than the faint edges of your target.

Colour — sky balance or photometric

Colour neutralises the sky and sets white balance. Choose Sky balance (works offline) or Photometric (SPCC), which measures real catalogue stars in your frame to get colour objectively right. Then, if the result is not quite to your taste, two sliders — Green ↔ Magenta and Cool ↔ Warm — shift the overall colour with a live preview. They multiply the channels rather than clipping one, so the colour differences between stars survive: an orange star stays orange next to a blue one. Seestar data tends to land slightly magenta, and that is the camera rather than the stacking, so a small nudge toward green is often all it wants. If you shot a dualband/LP target, Colourise and the Narrowband tool map that Ha + OIII data into a finished two-gas colour image in a single press.

Detail & stretch

Deconvolution sharpens tight star and structure detail while the data is still linear (BlurXTerminator, or a free fallback). Stretch is the big reveal — it pulls the faint signal up into the visible range. Recover Core tames blown-out galaxy and nebula cores (HDR), and Levels and Curves fine-tune the tones.

Finish

Saturation (with a masked nebula boost), Remove Green Fringe, Noise Reduction, Local Contrast and Star Reduction put on the final polish — each with a live preview and its own undo. Star reduction and the star-aware steps work even without RC-Astro, using a built-in star separator. Star Spikes can add artistic diffraction spikes if you like the look.

Enhancements & Export

Enhancements offers eleven tap-to-stack finishing moves — hue-selective colour boosts, vibrance, star colour, sky darken/lighten, dark structure, soft glow and nebulosity sharpening. Each tap is its own undoable nudge, so you can dial the effect in precisely. Export writes a finished 16-bit image (and, if you plate-solved, burns in the annotations and keeps the WCS in exported FITS).

Late fixes — Trim & fullscreen

Colour, at the end

Colour Balance (toolbar) is for the finishing colour work that used to mean exporting to another program. Pick a tonal range — shadows, midtones or highlights — and push it toward a colour; each range keeps its own settings, so you can warm the midtones and cool the highlights in one go. Then narrow Limit to so the change only touches a band of brightness: on a galaxy, that lets you colour the arms and leave the golden core alone. Tick Show the mask and the areas that will change light up while the rest dims, so you can see exactly where it lands. Your stars are separated out and laid back untouched, and because it appends to your history it never discards work you have already done — run it twice with different settings if you want.

Some problems only become visible once the image is stretched. A ragged stacking border at the frame edge is the classic one: invisible in the linear data, obvious at the end. Going back to the Crop step would work, but it discards every step taken since — an hour of work to remove twenty pixels. Trim exists for exactly this: it's a finishing tool, not a pipeline step, so it appends to your history rather than reaching back into it. Your whole edit survives, and undo still works.

To find those edge problems in the first place, press F for a distraction-free fullscreen canvas and pan and zoom around the frame. Esc brings the panels back.