Hegel’s Seven Planets

There is a persistent rumor, perpetuated primarily by historians of astronomy, that G.W.F. Hegel provided a logical proof that there could only be seven planets in the solar system. This diabolical proof supposedly lurks within his 1801 doctoral dissertation. However, in the only section that could possibly contain such a claim, that entitled ‘De orbitis planetarum’, the proof is difficult to spot:

While the displacements of the planets suggest an arithmetic progression in which, unfortunately, no planet in nature corresponds to the fifth member in the series, it is supposed that there really does exist between Mars and Jupiter, unbeknown to us, a planet moving through outer space. It is now being eagerly looked for …

Since this progression is arithmetic and does not follow a number series that generates them itself, i.e. not by powers, it is of no interest to philosophy. The extensive work of the Pythagoreans on the relations of philosophical numbers is well-known; so I will now, if I may, consider the traditional number series presented in the two Timaeus texts. For although Timaeus does not refer to the planets, he thinks the demiurge formed the universe according to this series. The number series is: 1, 2, 3, 4, 9, 16, 27, if I may take 16 instead of 8, which we find in the Timaeus. If this series really does give the true order of nature as an arithmetic series, then there is a great space between the fourth and fifth places where no planet appears to be missing.¹

If you missed Hegel’s seven-planets argument and are about to read the extract again, don’t bother—you won’t find it. What Hegel was attempting to do in ‘De orbitis planetarum’ was advance a counterargument to the newly formulated Bode’s Law, which gave a guide to the spacing between the planets (and was ultimately proven, roughly, true). Bode’s Law posited a ‘fifth’ planet between Mars and Jupiter, a body that was being actively sought during Hegel’s era. But Hegel says nothing of a logical necessity or proof of there being only seven planets, he simply introduces a counterargument—the progression he draws from Plato’s Timaeus—that indicates there isn’t a missing planet between Mars and Jupiter. Hegel is in no way dogmatic about his counterargument, as evinced by the contingency of the closing comment “If this series really does give the true order of nature …”.





Hegel ultimately lost this argument and Bode’s Law was upheld, so what happened to the phantom planet between Mars and Jupiter? Basically, the enormous gravitational pull of Jupiter ruled out any chance of a planet forming in the gap. The asteroid/dwarf planet Ceres² (discovered 1801, the year of Hegel’s dissertation) was considered a candidate at one point, but it is simply the largest body in the asteroid belt that takes the place of the missing planet. Hegel’s refutation of Bode’s Law may have been incorrect, as was his somewhat tentative claim that the planet the law predicts between Mars and Jupiter was not missing, but the story of a logical proof for seven planets is incorrect and more than a little uncharitable.


CITATIONS / NOTES:

1.  G.W.F Hegel, ‘De orbitis planetarum’, trans. David Healan, online here.
2.  Ceres was originally labelled a dwarf planet, then reclassified as an asteroid a year later, and ultimately reclassified a dwarf planet again in 2006.

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