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    "title": "Ewen and Purcell detect galactic hydrogen at the 21-centimeter line",
    "summary": "Ewen and Purcell observed radio emission from neutral hydrogen in the Milky Way near the 21-centimetre wavelength. Their 1951 report describes a signal concentrated near the Galactic plane, with a measurable frequency shift consistent with relative motion. The result gave radio astronomers a way to study hydrogen beyond regions visible in ordinary light.",
    "boundary": "The result concerns the reported fixed-beam observations and their frequency calibration. Dutch and Australian observations were separate follow-up reports. Inferring Galactic structure from the line requires additional observations and a model of gas motion.",
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    "year": 1951,
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        "title": "Detecting the Interstellar Hydrogen Line, 1951",
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        "id": "ewen-purcell-galactic-hydrogen-line-1951",
        "title": "Observation of a Line in the Galactic Radio Spectrum",
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        "date": "1951-09-01"
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            "citation": "Detecting the Interstellar Hydrogen Line, 1951",
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            "citation": "Observation of a Line in the Galactic Radio Spectrum",
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      "scope": {
        "description": "The result concerns the reported fixed-beam observations and their frequency calibration. Dutch and Australian observations were separate follow-up reports. Inferring Galactic structure from the line requires additional observations and a model of gas motion.",
        "domain": "Radio astronomy"
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      "sources": [
        {
          "citation": "Detecting the Interstellar Hydrogen Line, 1951",
          "url": "https://www.nrao.edu/archives/static/Ewen/ewen_HI.shtml"
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      "statement": "# Ewen and Purcell detect galactic hydrogen at the 21-centimeter line\n\nEwen and Purcell observed radio emission from neutral hydrogen in the Milky Way near the 21-centimetre wavelength. Their 1951 report describes a signal concentrated near the Galactic plane, with a measurable frequency shift consistent with relative motion. The result gave radio astronomers a way to study hydrogen beyond regions visible in ordinary light.\n\n## Scientific scope\n\nThe result concerns the reported fixed-beam observations and their frequency calibration. Dutch and Australian observations were separate follow-up reports. Inferring Galactic structure from the line requires additional observations and a model of gas motion.\n\n## Reading status\n\nThis is a source-linked WRS catalogue note. A full explanatory guide and independent scientific reconstruction have not been completed for this entry. Read the identified original work for its complete narrative and arguments.\n\n## People and systems\n\nH. I. Ewen; E. M. Purcell\n\nThese are the listed authors of the cited contribution sources. Paper authorship does not quantify individual effort. An incomplete list is explicitly marked; same names are not automatically merged.\n\n\n\n## Original sources\n\n- [Detecting the Interstellar Hydrogen Line, 1951](https://www.nrao.edu/archives/static/Ewen/ewen_HI.shtml)\n- [Observation of a Line in the Galactic Radio Spectrum](https://www.nature.com/articles/168356a0)\n",
      "summary": "Ewen and Purcell observed radio emission from neutral hydrogen in the Milky Way near the 21-centimetre wavelength. Their 1951 report describes a signal concentrated near the Galactic plane, with a measurable frequency shift consistent with relative motion. The result gave radio astronomers a way to study hydrogen beyond regions visible in ordinary light.",
      "title": "Ewen and Purcell detect galactic hydrogen at the 21-centimeter line"
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    "entry_id": "ewen-purcell-galactic-neutral-hydrogen-21cm-detection-1951",
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    "title": "Ewen and Purcell detect galactic hydrogen at the 21-centimeter line",
    "context": "Radio astronomy",
    "track": "Source-reported experimental result or reusable measurement method",
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    "what_changed": "Ewen and Purcell observed radio emission from neutral hydrogen in the Milky Way near the 21-centimetre wavelength. Their 1951 report describes a signal concentrated near the Galactic plane, with a measurable frequency shift consistent with relative motion. The result gave radio astronomers a way to study hydrogen beyond regions visible in ordinary light.",
    "scope": "Ewen and Purcell observed radio emission from neutral hydrogen in the Milky Way near the 21-centimetre wavelength. Their 1951 report describes a signal concentrated near the Galactic plane, with a measurable frequency shift consistent with relative motion. The result gave radio astronomers a way to study hydrogen beyond regions visible in ordinary light. The result concerns the reported fixed-beam observations and their frequency calibration. Dutch and Australian observations were separate follow-up reports. Inferring Galactic structure from the line requires additional observations and a model of gas motion.",
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    "references": [
      {
        "title": "Detecting the Interstellar Hydrogen Line, 1951",
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        "title": "Observation of a Line in the Galactic Radio Spectrum",
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