December 21 is the winter solstice, but the Sun's position, aka Horus, dies and remains in a very low horizon for about 3 days, then on the 25th he is born again. 

Also other Astrotheology myths associated but we get Hour and Horizon from Horus. 

In Spanish ¿Qué Hora es? 

Literally, Where is Horus? Or What hour is it? More appropriate is where it's the Sun. 

Nuttall

Correct over 50,000 years things have changed but man has tracked the great year 28,000 years twice in petroglyphs and cave paintings.

Basically within 10,000 years it was noticed that the Sun was in the lowest point in the northern hemisphere for 3 days. On the 25th the Sun was born to the new year and it began it's ascent into the sky. 

Yes December 21 and 22 is the winter solstice and shortest day of the year depending on orbital eccentricity and axial tilt.