Newton and Astrology

Unlike Ptolemy and Kepler (and to some extent Tycho), Newton never practiced astrology. In fact, Newton's laws spelled the end for any rational connection between astrology and astronomy. Ever since Newton, the two areas have developed independently. There are many examples of why; we show one here by considering the great alignment of the planets that occurred in 2002.

In May, 2002, all the normally visible members of the solar system were aligned so that they all appeared in the sky together. Here they are (picture by M. Rieke). It is frequently believed that such alignments have important effects on things that happen here on Earth, for example in the practice of astrology. There is no scientific evidence that would support these beliefs!

A sky chart for the same evening http://www.sfsidewalkastronomers.org/5planets/l516.html

We can evaluate how big these effects are likely to be. The following figure shows how the alignment came about.

(From Space.com, http://www.space.com/scienceastronomy/solarsystem/planets_align_020402-1.html)

Of the fundamental physical forces, only gravity has long enough range for all the planets to act on us in unison (the electric force has a similar range but is largely canceled by positive and negative charges). We can add up all the gravitational forces, using the astronomical unit (distance from sun to Earth) for the unit of distance and the mass of the earth for the unit of mass. Applying Newton's law of gravity, the forces of the planets are each in proportion to the mass of the planet, divided by the square of its distance from us. The pull of Jupiter is about 0.5% that of the moon, and that from ALL the other planets adds up to about another 0.1%. That is, the tidal force we felt from the alignment of all the planets together was changed by less than 1% from the force we would have felt from the moon alone. We know of NO other physical force that would have been nearly as important over these distances as gravity. On the surface of the earth, the gravitational force from the earth is about 300,000 times larger than that from the moon. Thus, there was essentially no perceptible change affecting us as a result of the alignment -- it would have been only a 1% change on a force that is 1/300,000 of the total we experience.

From a scientific perspective, we MUST conclude that even this super-alignment could have had no effect on our lives.