An Etymological Dictionary of Astronomy and Astrophysics
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The empirical rule relating the approximate distances of the → solar system  → planets from the → Sun. The original formulation was: a = (n + 4) / 10, where a is the mean distance of a planet from the Sun in → astronomical units and n = 0, 3, 6, 12, 24, 48, 96, 192 (doubling for each successive planet). The planets were seen to fit this sequence quite well, provided the → asteroids between → Mars and → Jupiter are counted as one planet, as did → Uranus discovered in 1781. However, → Neptune and the ex-planet → Pluto do not conform to the rule. The question of whether there is any physical significance to the "law," i.e. some dynamical reason that will explain planetary orbit spacing has led to much discussion during the past two centuries. Today, many astronomers are very skeptical and consider this "laws" to be numerical coincidence.

Named after the German mathematician Johann Titius (1729-1796), who first found the law in 1766, and the German astronomer Johann Elert Bode (1747-1826), who published it in 1772; → law.