Cosmic Rays and the Magnetic Field of the Moon

Abstract

IN a recent communication, S. Chapman¹ has calculated, on the basis of the theory of proportionality between magnetic moment and angular momentum developed recently by P. M. S. Blackett², that the ratio M_M/M_E between the magnetic dipole moment of the moon and that of the earth is 1/38,400. It may be readily shown that if this result is correct the magnetic field of the moon can only affect particles of primary cosmic radiation of very small energy, which are able to reach the earth only in the immediate vicinity of the geomagnetic poles. In fact, we have³ which on replacing M_M/M_E by Chapman‘s value, taking for the ratio D_M/R_E (D_M, distance from the earth to the moon; R_E, radius of the earth) its known value, and using for r_M the limiting value r_M = 0·414, gives r_E = 0·05 millistörmers, or approximately 0·1 MeV. (1 MeV. = 10⁶ eV.) if the primary particles are protons, 0·3 MeV. if electrons.