The sky on December 21, 2020 — as it really was

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]

   first quarter, 45% lit; the Moon was 398,738 km away.

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

   5.8 orbits of the Sun — 5,437 million km, that is 7,072 return trips to the Moon; 2,113 rotations of Earth; with the Sun — 42 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 121 million km away; today it is 245 million km (farther by 2×).

   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 30, 2028; Jupiter — in 2032; a full moon exactly on this date — December 20, 2029

   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/ap201221.html

   NASA APOD