The Celestial Spheres

The spheres began as a mathematician's answer to a philosopher's demand. Plato is said to have set the problem: to save the appearances of the wandering planets, their stations, retrogressions and varying brightness, using only uniform circular motion, the sole motion perfect enough for heaven. Eudoxus answered with nested concentric spheres, each planet carried by several, their combined rotations reproducing the observed wander. Aristotle took the geometry and made it physics: the spheres became real bodies of aether, the fifth element, incorruptible and naturally circular in motion, counted at fifty-five, each moved by its longing for the unmoved mover beyond.

Ptolemy's Almagest then made the scheme calculable, at the cost of elegance, with eccentrics and epicycles that strained the concentric picture while keeping its authority; his planetary order, Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn, became the canonical staircase. What resulted was not one theory but a civilization's furniture. The seven-story heaven organized the week's days, the alchemists' metals, the angelic hierarchies, the astrologers' dignities and the mystics' ascents; Islamic astronomy refined its parameters and Latin scholasticism baptized its movers. Lewis called the finished medieval model the greatest work of art the Middle Ages produced, and its genius was integration: physics, theology and imagination agreed, for once, about the shape of everything.

The demolition of the crystalline heavens took about seventy years and proceeded blow by blow. Copernicus, in 1543, moved the Earth but kept the spheres; his universe is still a nest of circles, only re-centered. The first crack was observational: the new star of 1572 and the comet of 1577, whose parallax Tycho Brahe measured with unprecedented care, both lay above the Moon, in the region where Aristotle's physics permitted no change, and Tycho showed the comet would have to smash through any solid spheres in its path. He concluded, in his own words, that the machinery of the heavens was not a hard and impervious body of orbs but fluid and open. Kepler delivered the structural blow in 1609: planetary orbits are ellipses, not circles, and no rotating sphere can carry an ellipse; the planets swim free, moved by a force from the Sun.

Galileo's telescope added indignities, mountains on the Moon, satellites around Jupiter, spots on the Sun, phases of Venus, each a small refutation of celestial perfection, and Newton in 1687 completed the transfer of explanatory power from geometry to gravitation, one law for apple and Moon alike. What fell with the spheres was more than an astronomy. The cosmos ceased to be a hierarchy with man at the humble center and God past the circumference; it became homogeneous space, the same physics everywhere. Pascal, mid-collapse, recorded the new sensation exactly: the eternal silence of those infinite spaces frightens me. The old model survives where it always lived best, in poetry, liturgy and the imagination of ascent.