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The sky on December 18, 2020 — as it really was

That day the Sun stood in Sagittarius — sign and constellation agree here.

РЫБЫОВЕНТЕЛЕЦБЛИЗНЕЦЫРАКЛЕВДЕВАВЕСЫСКОРПИОНЗМЕЕНОСЕЦСТРЕЛЕЦКОЗЕРОГВОДОЛЕЙ ♈︎♉︎♊︎♋︎♌︎♍︎♎︎♏︎♐︎♑︎♒︎♓︎ ♂︎22° ♀︎3° ☿︎26° ☉︎27° ♃︎29° ♄︎0° ☽︎16°

Bodies on the ecliptic (noon UTC)

  • ☉︎ Sun — 267.0° · sign Sagittarius · constellation Sagittarius
  • ☽︎ Moon — 316.6° · sign Aquarius · constellation Capricornus
  • ☿︎ Mercury — 266.1° · sign Sagittarius · constellation Ophiuchus
  • ♀︎ Venus — 243.5° · sign Sagittarius · constellation Scorpius
  • ♂︎ Mars — 22.0° · sign Aries · constellation Pisces
  • ♃︎ Jupiter — 299.8° · sign Capricorn · constellation Sagittarius
  • ♄︎ Saturn — 300.1° · sign Aquarius · constellation Capricornus
  • ☽︎ Moon 18% 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]

    waxing crescent, 18% lit; the Moon was 383,237 km away.

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

    5.8 orbits of the Sun — 5,450 million km, that is 7,088 return trips to the Moon; 2,118 rotations of Earth; with the Sun — 42.1 billion km around the Galactic centre, 1.6 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 117 million km away; today it is 243 million km (farther by 2.1×).

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

    That day fell in solar cycle 25, right at the minimum (10% through the cycle).

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

    Mars returns to that day’s point of its orbit on June 27, 2028; Jupiter — in 2032; a full moon exactly on this date — December 17, 2051

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

    The vernal point has shifted 288″ since that day; the real constellations now sit 24.2° away from the astrologers’ “signs”.

    precession 50.29″/yr
  7. Picture of the day [EXACT]

    NASA Astronomy Picture of the Day for this date: apod.nasa.gov/apod/ap201218.html

    NASA APOD

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