laurence
653ca103cd
Menorca sits inside the path of totality, but the geometry is extreme and it drives every decision in the plan: the Sun is 2 degrees above the horizon at maximum, on azimuth 288, and totality lasts 1 minute 12 seconds at Ciutadella before the Sun sets at 20:42. Two consequences follow from that 2 degrees. The light travels through roughly twenty times more atmosphere than at the zenith, so everything is dimmer, softer and redder than any published exposure table assumes and the histogram has to be the authority rather than a chart. And a low hill, a building or a haze bank on the sea horizon hides the entire event, so an unobstructed west-north-west view matters more than anything else about the site. That produces a genuine trade-off worth recording. Totality runs 1m38s at Mahon against 1m12s at Ciutadella, because the centre line favours the south-east - but Mahon is on the east coast, so from there the view towards 288 degrees crosses the island with Monte Toro in roughly that direction. Horizon beats duration: 26 extra seconds is a bonus, a blocked horizon is total loss. The plan therefore recommends a west or south-west coastal site. The plan also corrects an idea that was on the table: a photographic ND filter is not a solar filter. Standard NDs cut visible light while passing infrared largely unattenuated, which is where the heat is, and that will damage a sensor. The requirement is a certified ISO 12312-2 filter around OD 5 on the front of the lens, with the specific warning that Baader's AstroSolar Photo Film ND 3.8 is camera-only and unsafe to look through, while the ND 5.0 safety film does both jobs. The Star Adventurer GTi is explicitly excluded from eclipse day. Seventy-two seconds needs no tracking, and polar aligning in bright twilight towards a 2 degree Sun is impractical. It earns its place on the night skies of the same trip, not on the 12th. Kept in this repo rather than in a notes app because it is worked out from real numbers, it will be revised as the date approaches, and the reasoning behind each decision is the part worth keeping.
101 lines
4.5 KiB
Markdown
101 lines
4.5 KiB
Markdown
# astro-pipeline
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Processing and analysis code for remote-telescope imaging sessions, starting
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with iTelescope data from the [itelescope](https://git.discworld.casa/laurence/itelescope)
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drain campaign.
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The code lives here. **The data does not** - image sessions stay on disk (or
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wherever they are archived) and are addressed by an environment variable, so a
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session directory contains only pixels, results and a description of what was
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done to them.
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## What is here now
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`session-scripts/` - the 50 scripts that processed the NGC 5128 session of
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2026-07-21, exactly as they were run, plus the shared `layout.py` that tells
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them where files live. This is a working record rather than a finished product:
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the scripts were written in sequence as the work went along, several of them by
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parallel agents, and they show it. They are kept because they are the honest
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provenance of a set of published results, and because the productionised
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pipeline should be able to reproduce those results exactly.
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`session-scripts/restructure.py` - reorganises a flat session directory into the
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named layout below. Idempotent, dry run by default.
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`observing/` - plans for observing sessions that are not remote-telescope runs.
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Currently the total solar eclipse of 12 August 2026, seen from Menorca. These
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live here rather than in a notes app because they are worked out from real
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numbers, they get revised as the date approaches, and the reasoning behind each
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decision is worth keeping.
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## Pointing the scripts at a session
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```
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set ASTRO_SESSION=D:\astro\NGC5128\20260721 # Windows
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export ASTRO_SESSION=/data/astro/NGC5128/20260721 # POSIX
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python session-scripts/layout.py # prints the resolved layout
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```
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`layout.py` maps a **filename** to its subdirectory, so a script asks for
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`master-Red.fit` or `_stars.npz` and gets the right path without knowing the
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directory structure:
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| Directory | Holds |
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| `raw/` | exactly what the telescope delivered: archives and their preview jpegs |
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| `calibrated/` | uncompressed calibrated subs |
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| `stacks/masters/` | per-filter registered, plate-solved masters |
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| `stacks/original/` | alignment-only baseline stacks, no other processing |
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| `final/` | the deliverable renderings |
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| `renderings/` | other finished images |
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| `science/figures/` | analysis plots |
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| `science/catalogues/` | measured tables (CSV) |
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| `science/data/` | models, masks, derived quantities |
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| `science/notes/` | analysis write-ups |
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| `intermediates/` | caches a re-run can regenerate |
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Every session directory also carries its own `METHODS.md` describing what was
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done to that data and what was found - written for a reader who was not there.
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## Running order
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The scripts are named for their stage and run in this order:
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```
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unzip.py -> analyse.py -> stack.py -> solve.py -> depth.py
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-> compose.py -> hdr.py / enhance.py / starless.py / annotate.py
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-> final.py -> closeup.py -> triptych.py
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```
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The analysis families are independent of each other and of the renderings:
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`gc-*` (globular clusters), `sb_*` (surface photometry), `mo_*` (moving objects
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and transients).
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## Requirements
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Python 3.12 with numpy, scipy, astropy, scikit-image, sep, astroalign,
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photutils, astroquery, matplotlib, tifffile, Pillow.
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## Where this is going
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The next piece of work is a scheduler-driven pipeline: a staged CLI
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(`ingest -> calibrate -> measure -> register -> stack -> solve -> compose ->
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analyse`) with each stage resumable, packaged as an Apptainer image and driven
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by Slurm array jobs. Targets beyond mono LRGB: narrowband palettes, one-shot
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colour with debayering, other observatories' header conventions, and full
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calibration from bias/dark/flat for sources that do not pre-calibrate.
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Three findings from the first session are requirements for that build, not
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optional extras:
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1. **Vet moving-object candidates in detector coordinates.** Registration holds
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the sky still, so it drags detector-fixed defects across the frame on
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perfectly straight, constant-rate tracks. Hot pixels are better-behaved
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asteroids than real asteroids. This one cut took 141 confident spurious
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detections to zero.
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2. **Carry `r50/psf` through to any catalogue cross-match.** Comparing an
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aperture magnitude of a resolved source against a point-source catalogue
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like Gaia is meaningless, and looks exactly like a 2.8 magnitude outburst.
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3. **Never fit a sky background to a field the target fills.** A plane fitted
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around a large galaxy absorbs its halo - measured at -17.9 ADU/px here.
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Fit the background and a source model together.
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