The orbits traced by the paths of the planets around the sun are not equally spaced, but they do form a pattern. Noticing this pattern, J. B. Titius (1729-96) and J. E. Bode (1747-1826) developed a rule that predicts the spacing of the planets in our solar system. The spacing is roughly doubled from planet to planet.

A simple way to use Bode's law to predict the average distance of the planets from the sun is to begin with the following sequence of numbers. (Note that after the number 3, each number in the sequence is double that of its predecessor.)

     0, 3, 6, 12, 24, 48, 96, 192, 384, 768

Add 4 to each number:

     4, 7, 10, 16, 28, 52, 100, 196, 388, 772

Divide each by 10:

     0.4, 0.7, 1.0, 1.6, 2.8, 5.2, 10.0, 19.6, 38.8, 77.2

This gives a sequence of numbers representing each planet's average distance from the sun in Astronomical Units (AU). The following table shows how these predictions compare to the actual distance to each planet.

Planet	Bode's Law (AU)	Actual Distance (AU)
Mercury	0.4	0.39
Venus	0.7	0.72
Earth	1.0	1.00
Mars	1.6	1.52
The Main Asteroid Belt	2.8	2.8
Jupiter	5.2	5.20
Saturn	10.0	9.54
Uranus	19.6	19.19
Neptune	38.8	30.1
Pluto (dwarf planet)	77.2	39.1

As you can see, Bode's Law quite accurately describes the distances of the planets from the sun, with the exception of Neptune and Pluto (now a dwarf planet). You might also have noticed that Bode's Law predicts the existence of another planet between Mars and Jupiter. Instead, this is where we find the Main Asteroid Belt. Astronomers once thought that the Main Belt was the debris ring left over from a destroyed planet. But it's much more likely that such a planet was, in fact, prevented from ever forming by Jupiter's strong gravitational pull.

There is no scientific explanation for Bode's Law, and it may well be a simple mathematical coincidence. But it does provide a good and fun way to learn the relative distances between the planets.