August Eridanids

This somewhat diffuse radiant was noted by the Author while examining the 39,145 radio meteor orbits obtained by Zdenek Sekanina during the Radio Meteor Project of the 1960's. Six radio meteors were identified which suggest a duration of August 2-27. Maximum seems to occur around August 11/12 from an average radiant of RA=49.6 deg, DECL=-4.9 deg. What makes this stream orbit especially interesting is its similarity to the orbit of periodic comet Pons-Gambart (1827 II). The orbital plane is very similar, but the largest difference is in the perihelion distance, with the August Eridanids being 0.985 AU, and P/Pons-Gambart being 0.807 AU. The semi-major axis of the August Eridanids is 4.093 AU, while it is 14.944 AU for P/Pons-Gambart.

Interestingly, no visual evidence exists to directly support this radiant. However, there is strong evidence of activity 8 deg-10 deg north among the records of the American Meteor Society. Dr. H. L. Alden (South Africa) detected activity on August 11.7, 1926. R. A. McIntosh (New Zealand) detected activity on August 13, 1929. The Amateur Astronomers of the Franklin Institute (Pennsylvania) detected activity on August 17, 1941. Charles E. Worley (California) detected activity from the region of RA=45.0-48.0°, DECL=1.5-4.8° during August 7-9, 1954. Eli Metzger (Israel) detected activity on August 11, 1958.

Among the list of 5406 German radiants compiled by Cuno Hoffmeister in his 1948 book Meteorstrome, are three additional radiants which possess positions similar to those compiled from the American Meteor Society. They were detected during August 8-19, 1937, while Hoffmeister was observing from South-West Africa.

What seems to be indicated by this data, is that the August Eridanids are very old. The radio-echo stream and the visual stream are probably related and indicate an extensive mass separation has occurred.

Comet Pons-Gambart was only seen for a month in 1827. Its orbital period of 57.5 years is subsequently considered to possess an error of +/-10 years and no recovery has ever been made. Interestingly, in 1979, Hasegawa computed a parabolic orbit for a comet seen in 1110. He concluded that it is possibly identical to comet Pons-Gambart. Thus, there is evidence that this lost periodic comet has been in a similar orbit for nearly 1000 years.