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    "title": "Oort: how nearby stars reveal a rotating Galaxy",
    "summary": "Oort compares nearby stellar radial velocities and proper motions with a first-order differential-rotation model, finding a longitude-dependent velocity pattern supporting Lindblad's rotating Galactic system.\n\nA spinning galaxy does not have to rotate like a rigid wheel. Stars at different distances from its center can move at different angular speeds. From inside the Milky Way, that difference should leave a pattern in the velocities of stars seen in different directions. Oort derived the nearby-star pattern and compared it with available observations, turning a Galactic rotation hypothesis into a testable kinematic model. The radial signal changes with direction and roughly with distance in the approximation used. Proper motions supplied another, more uncertain check. The paper helped make the Galaxy a dynamical system that could be investigated from local measurements, while leaving its full rotation curve, mass distribution and accurate dimensions unsettled.",
    "boundary": "Circular-orbit/low-random-motion and small-distance-to-Galactic-radius assumptions justify first-order local formulas; higher orders are neglected. Longitude-harmonic velocity fits and tentative proper-motion agreement support differential rotation, not a unique global mass model or every Galactic component's circular motion. Distance/parallax spread, solar motion, sample selection and precession corrections are uncertain; corrected final proof note revises the provisional force ratio/center distance, so earlier figures must not stand as final paper estimates. Historical coordinates and scales are not present-day Milky Way parameters. Solid-body rotation can have zero radial differential signal, so a null harmonic is not proof of no rotation. The paper's light-obscuring dark material is not a detection of modern nonbaryonic dark matter. The account does not independently reconstruct the complete data and force-law analysis or verify every formula and table. Later rotation curves, modern dark-halo claims, radio mapping and the 1950 comet reservoir are distinct.",
    "area": "Galactic differential rotation",
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        "title": "Sonoma State University astronomy: Jan Hendrik Oort identity and1927 bibliography",
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        "description": "Circular-orbit/low-random-motion and small-distance-to-Galactic-radius assumptions justify first-order local formulas; higher orders are neglected. Longitude-harmonic velocity fits and tentative proper-motion agreement support differential rotation, not a unique global mass model or every Galactic component's circular motion. Distance/parallax spread, solar motion, sample selection and precession corrections are uncertain; corrected final proof note revises the provisional force ratio/center distance, so earlier figures must not stand as final paper estimates. Historical coordinates and scales are not present-day Milky Way parameters. Solid-body rotation can have zero radial differential signal, so a null harmonic is not proof of no rotation. The paper's light-obscuring dark material is not a detection of modern nonbaryonic dark matter. The account does not independently reconstruct the complete data and force-law analysis or verify every formula and table. Later rotation curves, modern dark-halo claims, radio mapping and the 1950 comet reservoir are distinct.",
        "domain": "Galactic differential rotation"
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      "sources": [
        {
          "citation": "J.H.Oort, Observational evidence confirming Lindblad's hypothesis of a rotation of the galactic system (1927),275-282",
          "url": "https://articles.adsabs.harvard.edu/pdf/1927BAN.....3..275O"
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        {
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      "statement": "# Oort: how nearby stars reveal a rotating Galaxy\n\nOort compares nearby stellar radial velocities and proper motions with a first-order differential-rotation model, finding a longitude-dependent velocity pattern supporting Lindblad's rotating Galactic system.\n\nA spinning galaxy does not have to rotate like a rigid wheel. Stars at different distances from its center can move at different angular speeds. From inside the Milky Way, that difference should leave a pattern in the velocities of stars seen in different directions. Oort derived the nearby-star pattern and compared it with available observations, turning a Galactic rotation hypothesis into a testable kinematic model. The radial signal changes with direction and roughly with distance in the approximation used. Proper motions supplied another, more uncertain check. The paper helped make the Galaxy a dynamical system that could be investigated from local measurements, while leaving its full rotation curve, mass distribution and accurate dimensions unsettled.\n\n## Scientific scope\n\nCircular-orbit/low-random-motion and small-distance-to-Galactic-radius assumptions justify first-order local formulas; higher orders are neglected. Longitude-harmonic velocity fits and tentative proper-motion agreement support differential rotation, not a unique global mass model or every Galactic component's circular motion. Distance/parallax spread, solar motion, sample selection and precession corrections are uncertain; corrected final proof note revises the provisional force ratio/center distance, so earlier figures must not stand as final paper estimates. Historical coordinates and scales are not present-day Milky Way parameters. Solid-body rotation can have zero radial differential signal, so a null harmonic is not proof of no rotation. The paper's light-obscuring dark material is not a detection of modern nonbaryonic dark matter. The account does not independently reconstruct the complete data and force-law analysis or verify every formula and table. Later rotation curves, modern dark-halo claims, radio mapping and the 1950 comet reservoir are distinct.\n\n## People and systems\n\nJan Hendrik Oort\n\n\n\n## Original sources\n\n- [J.H.Oort, Observational evidence confirming Lindblad's hypothesis of a rotation of the galactic system (1927),275-282](https://articles.adsabs.harvard.edu/pdf/1927BAN.....3..275O)\n- [Sonoma State University astronomy: Jan Hendrik Oort identity and1927 bibliography](https://phys-astro.sonoma.edu/brucemedalists/jan-oort)\n",
      "summary": "Oort compares nearby stellar radial velocities and proper motions with a first-order differential-rotation model, finding a longitude-dependent velocity pattern supporting Lindblad's rotating Galactic system.\n\nA spinning galaxy does not have to rotate like a rigid wheel. Stars at different distances from its center can move at different angular speeds. From inside the Milky Way, that difference should leave a pattern in the velocities of stars seen in different directions. Oort derived the nearby-star pattern and compared it with available observations, turning a Galactic rotation hypothesis into a testable kinematic model. The radial signal changes with direction and roughly with distance in the approximation used. Proper motions supplied another, more uncertain check. The paper helped make the Galaxy a dynamical system that could be investigated from local measurements, while leaving its full rotation curve, mass distribution and accurate dimensions unsettled.",
      "title": "Oort: how nearby stars reveal a rotating Galaxy"
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    "id": "oort-galactic-differential-rotation-1927",
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    "title": "Oort: how nearby stars reveal a rotating Galaxy",
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    "evidence_summary": "Source-linked, scoped account of the original work. The published scope states the scientific assumptions and remaining verification limits. WRS has not independently certified the full proof, experimental result or system benchmark.",
    "references": [
      {
        "title": "J. H. Oort, Observational evidence confirming Lindblad's hypothesis of a rotation of the galactic system (1927),275-282",
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