  The Poynting-Robertson (P-R) effect has been applied to meteoroids for
several decades. It is well known that the P-R effect produces only changes in
the orbital plane of the particle. The differential equations governing the
secular changes in both eccentricity and semi-major axis are known since the
time of Robertson, provided the initial orbits are not near circular. A
disadvantage of this type of osculating orbital elements is that it cannot be
applied to motion of arbitrarily shaped particles. Relevant type of osculating
orbital elements is discussed. It's application to the P-R effect is presented
and simple analytical formulae for secular changes in both eccentricity and
semi-major axis are derived.
