I think that the ancients realized this relationship through yoga and self study.
By observing the body’s cycle superimposed over the calendar’s these sages and shamen made predictions based on their understanding of the celestial dynamics. As records and observations improved, the calendar has changed significantly and holidays moved to suit these observations. The heliocentric understanding of universe seemed absurd until Galileo re-interpreted the existing data into a new paradigm. The world remained unchanged, but our understanding of it was forever transformed.
If you look at holidays (most of which which pre-date our present calendar systems) they all acknowledge the winter solstice as a significant date. I think that this is because the winter solstice is the most basic astronomical marker that pre-industrial peoples had for the perihelion (the point that earth is closest to the sun). Think Stonehenge. That’s why Christmas, Diwali, Hanukah, New Years are all celebrations of the ‘holiday spirit’ . That’s why people are all hyped up around the holidays. Not only because they are being affected by social pressures like family, but because the earth is moving fast and close to the sun. The earth is in fact 2.3 million miles closer to the sun in January than in July. Orbital mechanics require that the length of the seasons be proportional to the areas of the seasonal quadrants, so when the eccentricity is extreme, the seasons on the far side of the orbit can be substantially longer in duration. When autumn and winter occur at closest approach, as is the case currently in the northern hemisphere, the earth is moving at its maximum velocity and therefore autumn and winter are slightly shorter than spring and summer. Thus, summer in the northern hemisphere is 4.66 days longer than winter and spring is 2.9 days longer than autumn.
This explains the autumn agitation (a time of fasting a reflection i.e Ramadan and Jewish high holidays which require repentance) The creepy feelings of Halloween and Day of the Dead, The autumn feast as the body takes on more and more energy from the sun, the frenzy of the holiday build up, then a brief moment of calm as we round the bend (christmas, new years, etc) followed a quick change of direction and a fall off into depression, weight gain, seasonal affected disorder. The balance returns around early spring, (although this recovery is itself augmented by the natural human hormonal mating cycles of springtime). Lastly are the torpor of the dog days which I guess are not caused by summer heat but the maximal distance and minimal orbital velocity of the earth in July and August
In sum; the traditional winter holidays, astrology, calendar are all memorializing the seasonal feelings not the relative position of the sun to the horizon. Not the other way around.