SJAA Ephemeris February 2001 | SJAA Home | Contents | Previous | Next

The Night between the Centuries

Guy Ottewell


Birth comes in darkness, flowers into day. The wave of dark we call "the night of December 31 / January 1" separates, as it rolls around the planet, a past space of light and a future space of light. As do all waves before and after; but in this case the past was a part of the Twentieth Century, the coming day is out in the Third Millenium.

This is an artificial count imposed on the eternal train of waves, no real transition. Yet it could be: it could be during this special night that you decide to become a different person - a poem is conceived - an insight leads to a new age. To show it could happen, it has happened before. The artificial transition of exactly two hundred years ago did coincide with such a real transition. There are insights that come at night because we are undistracted, half-dreaming, and there are out-sights that come at night for the physical reason that we are facing outward from the Sun. The night between the eighteenth and nineteenth centuries was one of the upward steps in our perception of the cosmos. Not one of the few greatest steps, but one of the sharpest.

The cosmos, once, was the vast earth we stand on and the ungraspable sky. The sky consisted of the misty air, and above that the seven lanterns that fidget like beings, Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn, and beyond them the ceiling of stars. In 1543 Copernicus rearranged all (Aristarchus had thought of it eighteen centuries earlier, but was dismissed): Sun in the middle; circling around it Mercury, Venus, Earth, Mars, Jupiter, Saturn, stars. Since then, it has remained only to feel the star-shell, sort it into such distances that the former cosmos dwindles to a grain within it.

And, nearer home, to sort the distances between the planets. They grow gradually farther apart, rather like the widening spiral of a nautilus shell: each is not quite twice as far outward as the last. Surely there is some divine regularity in this spacing? Johannes Kepler conceived (on July 19, 1595) the beautiful idea that if the planets are set in concentric spheres, then the five "Platonic solids" or regular polyhedra (tetrahedron, cube, octahedron, dodecahedron, icosahedron) could fit between them. In 1766, Johann Daniel Titius of Wittenberg pointed out (in his translation of someone else's book) a less fantastic rule, which in 1772 Johann Elert Bode added as a footnote to a textbook of his own; it is known as Bode's Law or the Titius-Bode Law. If we call the distance of Mercury from the Sun 4, then Venus is at 4+3=7, Earth 4+6=10, Mars 4+12=16, Jupiter 4+48=52, Saturn 4+96=100. It works quite well. Divide these numbers by 10 and you have the distances as we now reckon them in "astronomical units" (Earth's as 1); not precisely, but within a decimal digit or so. In 1781 William Herschel discovered the first new planet, Uranus. It was indeed at 4+192=196! (or near enough). Bode's "Law" seemed confirmed as a fact of nature.

Except - what about 4+24=28, the fifth position? There was no planet here! Only a suddenly larger and logically intolerable leap from Mars to Jupiter.

The missing planet's distance, obviously, was known, hence its speed of motion, and like the other planets it must move along the zodiacal band of the sky (whose center is the ecliptic). The serious search for it was organizaed by Baron Francis Xavier von Zach, in 1800. He divided the zodiac into 24 15-degree sections and assigned them to the astronomers of Europe. The most outlying, though in the best climate, was Father Piazzi, in Sicily; and one of the twists of the tale is that Piazzi had not yet learned of his role, and had not received the star-charts of the block of sky he was to search, by the end of the year; so that he did not know he was suppoed to be helping solve the problem when he solved it. He was at work on a different project. As so often, someone like Herschel or Piazzi patiently surveying stars (or, in our time, asteroids) discovers something by what Horace Walpole called serendipity - in the manner of the fairy-tale Three Princes of Serendip or Ceylon, who sailed in search of one thing and kept finding others.

Bode's "Law" - unlike the universal laws of Newton that explained Kepler's laws of motion, that in turn explained Copernicus - was a descriptive rule that worked only so far. Though it seemed reconfirmed when Ceres was found at the missing position, after that it broke down. Neptune, when found in 1846 as a delayed consequence of the discovery of Uranus, was not at the next position but well short of it (not at 38.8 astronomical units but at 30); and Pluto, found as an even more indirect consequence in 1930, was not at 77.2 a.u. but at 39 where Neptune should have been.

And Ceres was not "the missing planet." It was far too small; and then other small bodies began to be found in the same region; the first by Olbers in March 1802, another by Harding in 1804, another by Olbers in 1807; they continued to be given, like the planets, the names of great dieties - Pallas, Juno, Vesta. Then came a hiatus of 38 years; but the discoveries resumed, with a vengeance, so that known asteroids now number in the thousands, unknown ones probably in the millions. The status of Ceres is that it was the first and largest of this new class of bodies, rather as Pluto is now proving to be the first and largest of the "Kuiper Belt" or Transneptunians.

The story is one of coincidences (Ceres was discovered on 1801 Jan. 1, definitely recovered on 1802 Jan. 1) and manifold aspects (the gap occupied by the asteroids also divides the inner "terrestrial" rocky planets from the outer "Jovian" gas giants). And it involves many of the mathematician-physicist-astronomers of the time: Bode himself; Lalande; Laplace; Euler, who "saw beauty bare" in that his simple equation ties together all shapes (the number of vertices minus edges plus faces minus solids equals one); Lexell, whose comet (even more than Brook's which we see this year) played dangerously close games with Jupiter and also with the Earth; Heinrich Olbers of the Olbers Paradox (if the universe is uniform and infinite the starry sky should be as bright all over as the Sun); and Gauss, who used the crisis to push mathematics as well as astronomy into an advance.

Footnote: On Oct. 19, 2000, while writing this, I found myself called downstairs by Professor of Chemistry Tony Arrington to a party for the Hundredth Birthday of the Photon. A crowd ate a cake on which an icing artist at a local store had had to trace the most elaborate design of his life, embodying the graphs and equations with which Max Planck founded quantum mechanics on this date in 1900.

[Ceres will have an opposition in 2001 on July 7, and should visible all summer around Sagittarius. - Ed.]

[Reprinted with permission from the Astronomical Calendar 2001, Copyright (C) 2000 Guy Ottewell. Published by Universal Workshop, Furman University, Greenville, S.C. http://www.universalworkshop.com]


Mail to: Guy Ottewell
Copyright © 2001 San Jose Astronomical Association
Last updated: July 19, 2007

Previous | Contents | Next