LXXI. Determination of meteor radiants by observation of radio echoes from meteor trails

The rate of occurrence and the ranges of the radio echoes from meteor trails vary with time as the radiant moves across the heavens. This variation is explained and the ranges are estimated for any position of the radiant, on the assumption that the echoes are due to broadside reflection from meteor trails. Such theoretical estimates are shown to agree well with experimental results. The change in the rate and ranges is more marked for a highly beamed aerial, and it is shown that with a horizontally narrow beam directed at sufficiently low elevation the ranges attain a sharp maximum when the azimuth of the radiant differs from that of the beam by 90°. This forms the basis for a method of radiant determination. For the known showers analysed so far the results obtained for the radiant coordinates are consistent with those given by visual observers, and it is shown how the method can be used for the determination of unknown radiant positions. The accuracy depends on the echo rate, the declination of the radiant and the width and elevation of the aerial beam. Using an aerial systenl whose half-amplitude beam width is ±10° it is possible, under the most favourable circmnstances, to place the radiant within a circle of radius 1°, but this degree of precision cannot usually be attained, and probable errors of ±2° in right ascension and ±3° in declination are more common.