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No. 10: Spring 1980

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Long-delayed radio echoes

J. Hals first observed long-delayed radio echoes in 1927. During the following half-century, scientists have been studying this perplexing problem, but it has been the amateurs who have accumulated the bulk of the data. Over 100 reports exist where echoes of radio transmissions were received seconds later at the original transmitting station. Since light travels 186,000 miles per second, any simple radio-wave reflector would have to be well beyond the moon's orbit.

A wide variety of natural phenomena (interplanetary matter) and even artificial devices (alien space probes) have been postulated to explain the long delays. Muldrew's article is first of all an excellent summary of the long and fascinating history of this effect. His bibliography is extensive and apparently nearly complete.

Muldrew next examines the various ionospheric mechanisms that might cause long delays. The ionosphere is a complex structure with ducts in which radio signals can get trapped. Delays of a second or so might be due to such trapping but the longer delays require some other explanation. Muldrew favors a rather complex interaction between signals from separate transmitters that (theoretically at least) can create a long-lived electrostatic wave that travels in the ionosphere -- a sort of natural memory device. The coded signals could then be read out much later when the proper natural conditions developed. Delays of up to 40 seconds might be possible with this "ionospheric memory."

(Muldrew, D.B.; "Generation of Long Delay Echoes," Journal of Geophysical Research," 84:5199, 1979.)

References. More information on these curius echoes is located at GER1 in our Catalog: Rare Halos, Mirages. For a description of this book, visit: here.

From Science Frontiers #10, Spring 1980. 1980-2000 William R. Corliss

Science Frontiers Sourcebook Project Reviewed in:


  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

  • "An interesting, systematic presentation of unusual weather [..] This book is recommended for a general audience" --"Corliss, William R., Tornados, Dark Days, Anomalous Precipitation, and Related Weather Phenomena, Sourcebook Project, 1983.", revieweed in Choice, September 1983
  • "..the science is necessarily somewhat speculative, but Corliss's symthesis is based on reputable sources." -- "Corliss, William R. (Compiler). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena" reviwed by Joseph M. Moran, Univ. of Wisconsin in Science Books and Films, Sep/Oct 1983

  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada, Vol. 81, no. 1 (1987), p. 24., 02/1987