{
  "abstract": "All-sky cameras support weather monitoring, amateur astronomy, fireball and space-debris detection, and measurements of light pollution. These applications require reliable astrometric calibration despite imperfect camera alignment and variable observing conditions. We present an open-source procedure that combines a compact fisheye model, an exact rotation to account for camera tilt, and automatic star matching. It can initialise a calibration from a single frame given the observing site coordinates and observation time. We evaluate the procedure on nine cloud-free, moonless frames, obtained with a Raspberry Pi camera and a 1.55 mm lens. Fitting on eight frames and evaluating on the ninth in turn gives a median residual of 0.70 px (95% interval 0.64-0.80 px) across 4172 matches, reduced to 0.60 px by two optional decentering parameters. All nine single-frame calibrations pass the quality criteria and predict positions on other frames with a median residual of 0.77 px. We also apply the clear-sky calibration to 73 frames with varying lunar illumination or cloud cover, obtaining comparable residuals for accepted matches on moonlit frames (0.62 px). These results support reusing a calibration while the camera geometry remains unchanged and enough stars remain visible for reliable matching. To test the generality of the single-frame procedure, we calibrated one night frame from each of 23 different all-sky systems, including fireball-network cameras, observatory sky monitors and amateur stations, with images of 0.3 to 77 megapixels in JPEG, FITS and camera-raw formats. All 23 are calibrated from the site and time alone, with a median fit residual of 0.42 px. Applied to a second frame of the same camera without refitting, the calibrations give a median residual of 0.66 px over 18 systems. The procedure is available as the Python package ascal.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": "Journal reference: The Open Journal of Astrophysics, Vol. 9, 173392 (2026)",
  "arxiv": "2609.15724",
  "author_total": 4,
  "authors": [
    {
      "name": "J. R. González Fernández"
    },
    {
      "name": "Laura Hermosa Muñoz"
    },
    {
      "name": "María Fernández Alonso"
    },
    {
      "name": "Lucía González Cuesta"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/307pbs7nn7zzw.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.15724",
  "fulltext_url": null,
  "id": "307pbs7nn7zzw",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.15724",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.IM"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2609.15724",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-29",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/307pbs7nn7zzw.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:36:22Z",
      "native_id": "2609.15724",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.15724"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.IM",
      "subfield": "instrumentation-methods"
    }
  ],
  "title": "Automatic astrometric calibration of low-cost all-sky cameras",
  "title_text": "Automatic astrometric calibration of low-cost all-sky cameras",
  "type": "preprint",
  "updated_at": "2026-11-04T15:20:50Z",
  "url": "https://research.draconitic.com/paper/307pbs7nn7zzw",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.33232/001c.173392",
      "pid": "0j068yjs3wg3r",
      "relation": "published-as",
      "title": "Automatic astrometric calibration of low-cost all-sky cameras",
      "venue": "The Open Journal of Astrophysics"
    }
  ]
}