Earthrise--in the Before Times

[SorellaLaBefana]

2. So Very True

Even now, if one just goes out and looks up at the celestial sphere, it seems Quite Clear that the universe is rotating around an immobile Earth

It was only after millenia of peoples all over the world looking at the stately and awe-inspiring movements of the night sky that it first became possible to predict many of these movements, and to then begin to explain why most of the movements *were* predictable. Comets remained a problem, and were simply ascribed to being Signs from God(s).

It is interesting to realize that when first developed the Copernican heliocentric model was less accurate in predicting planetary motions than the much older Ptolemaic geocentric model which had been adjusted for well over a thousand years using epicycles (circles within circles) to make things come out right. This is because Copernicus retained the "perfect motion" of a circle for his orbits and thus still had to use some epicycles—although fewer. Not until Kepler replaced circular orbits with the "less perfect" but actually existent elliptical orbits was this resolved.

This change only occurred almost a century after Copernicus when Kepler (who was a student of Tycho Brahe, and whose observations allowed Kepler to develop his Laws of Planetary Motion) realized that replacing circles with ellipses allowed all epicycles to be discarded.

Also interesting, is that Brahe supported neither the Copernican nor the Ptolemaic models, but had worked out his own (as best I know) compromise of a geo-heliocentric solar system.

https://media.sciencephoto.com/image/c0145205/800wm/C0145205-Epicycles_of_Moon_s_orbit,_1708.jpg
Credit ROYAL ASTRONOMICAL SOCIETY (Can't make this autoshow on DU, it's worth clicking on though!)

Epicycles of Moon's orbit. This is plate 18 from the 1708 edition of the star atlas 'Harmonica Macrocosmica' by the Dutch-German mathematician and cosmographer Andreas Cellarius (1596-1665). It shows eight epicycles for the Moon's orbit round the Earth. Epicycles were mathematical constructs used to explain geocentric orbits before heliocentric models simplified the calculations. Insets (lower right and left) show the crescent, new and full Moon. 'Harmonica Macrocosmica', first published in 1660, had 30 colour plates with Latin text. This edition was published in Amsterdam by Petrus Schenk and Gerard Valk.

https://www.sciencephoto.com/media/480551/view