Sky on December 21, 2017: where the Sun, Moon and planets really were

The real sky on December 21, 2017: Sun in Sagittarius (horoscope says "Sagittarius"), Moon 9% lit, planet positions from ephemerides.

The sky on December 21, 2017 — as it really was

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

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

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

The Moon that day [EXACT]
waxing crescent, 9% lit; the Moon was 404,507 km away.
astronomy-engine
How far Earth has travelled since [EXACT]
8.8 orbits of the Sun — 8,257 million km, that is 10,740 return trips to the Moon; 3,209 rotations of Earth; with the Sun — 63.8 billion km around the Galactic centre, 2.5 light-days.
29.78 km/s along the orbit; 230 km/s around the Galactic centre
Mars then and now [EXACT]
On that day Mars was 306 million km away; today it is 246 million km (closer by 1.2×).
astronomy-engine; checked against JPL Horizons for 2026-09-14
Solar cycle [ESTIMATE]
That day fell in solar cycle 24, on the decline (82% through the cycle).
SILSO smoothed minima
When the sky repeats [EXACT]
Mars returns to that day’s point of its orbit on May 18, 2027; Jupiter — in 2029; a full moon exactly on this date — December 20, 2029
sidereal periods: Mars 686.98 d, Jupiter 11.862 yr
How far the sky has drifted since [EXACT]
The vernal point has shifted 432″ since that day; the real constellations now sit 24.1° away from the astrologers’ “signs”.
precession 50.29″/yr
Picture of the day [EXACT]
NASA Astronomy Picture of the Day for this date: apod.nasa.gov/apod/ap171221.html
NASA APOD

Computed from the date only; nothing about you is stored.