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The sky on December 13, 1973 — as it really was

That day the Sun stood in Ophiuchus, while the horoscope says "Sagittarius". The gap is 23.5° of precession.

РЫБЫОВЕНТЕЛЕЦБЛИЗНЕЦЫРАКЛЕВДЕВАВЕСЫСКОРПИОНЗМЕЕНОСЕЦСТРЕЛЕЦКОЗЕРОГВОДОЛЕЙ ♈︎♉︎♊︎♋︎♌︎♍︎♎︎♏︎♐︎♑︎♒︎♓︎ ☽–☿ 117.4°☽–♃ 178.8°☿–♀ 57.1° ♂︎27° ♄︎2° ☽︎9° ☿︎6° ☉︎21° ♀︎3° ♃︎10°

Bodies on the ecliptic (noon UTC)

  • ☉︎ Sun — 261.3° · sign Sagittarius · constellation Ophiuchus
  • ☽︎ Moon — 129.4° · sign Leo · constellation Cancer
  • ☿︎ Mercury — 246.8° · sign Sagittarius · constellation Scorpius
  • ♀︎ Venus — 303.9° · sign Aquarius · constellation Capricornus
  • ♂︎ Mars — 27.2° · sign Aries · constellation Pisces
  • ♃︎ Jupiter — 310.6° · sign Aquarius · constellation Capricornus
  • ♄︎ Saturn — 92.1° · sign Cancer · constellation Gemini
  • ☽︎ Moon 83% illuminated

astronomy-engine ephemerides (VSOP87/ELP), IAU 1930 constellation boundaries. Positions accurate to a fraction of a degree.

The day’s dossier, from real data

Checkable facts with a tag and a source; the classical reading is in the chart.

  1. The Moon that day [EXACT]

    waning gibbous, 83% lit; the Moon was 363,776 km away.

    astronomy-engine
  2. How far Earth has travelled since [EXACT]

    52.8 orbits of the Sun — 49,628 million km, that is 64,553 return trips to the Moon; 19,288 rotations of Earth; with the Sun — 383.3 billion km around the Galactic centre, 14.8 light-days.

    29.78 km/s along the orbit; 230 km/s around the Galactic centre
  3. Mars then and now [EXACT]

    On that day Mars was 103 million km away; today it is 245 million km (farther by 2.4×).

    astronomy-engine; checked against JPL Horizons for 2026-09-14
  4. Solar cycle [ESTIMATE]

    That day fell in solar cycle 20, on the decline (81% through the cycle).

    SILSO smoothed minima
  5. When the sky repeats [EXACT]

    Mars returns to that day’s point of its orbit on June 29, 2028; Jupiter — in 2032; a full moon exactly on this date — December 13, 2046

    sidereal periods: Mars 686.98 d, Jupiter 11.862 yr
  6. How far the sky has drifted since [EXACT]

    The vernal point has shifted 2,628″ since that day; the real constellations now sit 23.5° away from the astrologers’ “signs”.

    precession 50.29″/yr

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