Epsilon Geminids

Observing

The duration of this meteor shower extends from October 10 to 27, with a maximum of 1-2 meteors per hour occurring on October 19 (λ=206°), from α=103°, δ=+25°. The radiant's daily motion is +0.7° in α and -0.1° in δ.

History

The first instance of this shower being recognized as a fairly consistent producer of meteor activity was in 1899, when W. F. Denning listed a shower called the Delta Geminids in his great "General Catalogue of Radiant Points of Meteoric Showers and of Fireballs and Shooting Stars observed at more than one Station." Although the shower was listed as being active from September through January, it is obvious after examining Denning's list that several streams were responsible for the activity---most notably, a shower was definitely active shortly after mid-October.

According to Denning's article, the first sighting of this shower may have been on October 19, 1868, when T. W. Backhouse (Sunderland) plotted 6 meteors from RA=100 deg, DEC=+18 deg. Denning had observed the shower on two occasions, the first being October 15-20, 1879 (RA=106 deg, DEC=+23 deg), and the second being October 14-21, 1887 (RA=105 deg, DEC=+22 deg). Other probable radiants were also listed, including one observed by D. Booth (Leeds) during October 15-20, 1887 (RA=99 deg, DEC=+22 deg), which apparently confirmed Denning's observation of the same year and might indicate a stronger than normal return.

Since 1899, observations of this shower have occasionally appeared in the literature, but these were purely accidental observations, as no specific searches were carried out. During October 18, 20 and 24, 1922, J. P. M. Prentice plotted 13 very rapid meteors from an average radiant of RA=103.5 deg, DEC=+18.5 deg. On October 25, 1932, Ernst Öpik's Arizona Expedition for the Study of Meteors obtained an excellent radiant determination of RA=108 deg, DEC=+25 deg.

C. Hoffmeister (Germany) was the next person to recognize an active mid-October shower in Gemini. In his classic book Meteorströme, Hoffmeister listed a shower with an average radiant of RA=101°, DEC=+26°. This shower had been noted on 12 occasions between 1909 and 1933, and the probable date of maximum was October 19 (solar longitude=206°). This book was published in 1948, but the Epsilon Geminids again fell into obscurity.

The shower was next "discovered" in 1958, when R. E. McCrosky and A. Posen (Harvard College Observatory, Massachusetts) identified six photographic meteor orbits from data gathered during the Harvard Meteor Project of 1952-1954. The indicated duration of activity was October 17 to 27, and the date of maximum was believed to be October 17. The average radiant position was RA=102°, DEC=+26°.

The shower's next milestone came in 1960, when it was first detected by radio-echo techniques. B. L. Kashcheyev and V. N. Lebedinets (Kharkov Polytechnical Institute, USSR) isolated thirteen Epsilon Geminids during October 10-27. The date of the nodal passage was indicated as October 16 (solar longitude=203 deg), at which time the average radiant was RA=104°, DEC=+25°. Interestingly, this has remained the only radio-echo survey to reveal any trace of this stream.

The first visual study of this shower was conducted by V. Znojil (Public Observatory, Brno, Czechoslovakia) in 1965. It began with telescopic observations from Boleradice and Bohuslavice (Czechoslovakia). Observations were made during October 20-25, with Epsilon Geminids being detected each day. Maximum may have occurred on October 22 (though the low activity obtained by the telescopic observations made the exact date difficult to determine), at which time the average radiant was at RA=103°, DEC=+25°. The radiant's daily motion was given as +0.7° in RA and +0.2° in DEC. Znojil combined these observations with previous studies conducted by Hoffmeister (1948), McCrosky and Posen (1958 & 1961), Southworth and Hawkins (1963), and Kashcheyev and Lebedinets (1967) and concluded that the shower reached maximum at a solar longitude of 204.4°. The average radiant was determined as RA=101.8°, DEC=+26.2° and Znojil's revised estimate of the radiant's daily motion was +0.7° in RA and -0.1° in DEC.

Several amateur astronomers have observed this shower in recent years. During October 15-28, 1979, Mark Adams observed 19 Epsilon Geminids in 18 hours 36 minutes and determined the average magnitude as 3.32. He estimated that the maximum rate reached 1-3 per hour. R. Lunsford (California) observed 11 Epsilon Geminids in 24 hours during October 15-21, 1980, and noted that the average magnitude was 2.73. Jeff Wood, director of the meteor section of the National Association of Planetary Observers (Western Australia), gives the shower's duration as October 14-27. He concluded that a maximum rate of 1-2 meteors per hour was detected on October 20, from RA=104°, DEC=+26°.

What makes the Epsilon Geminids such an interesting stream is that it bears a strong resemblance to the Orionids, except that the argument of perihelion and ascending node are reversed by about 180 deg. During 1963, Richard B. Southworth and Gerald S. Hawkins pointed out that the orbit of the Epsilon Geminids was similar to the Orionid orbit, but they showed that the major differences between the orbits were in inclination (9 deg) and longitude of perihelion (34°). In 1968, Znojil and J. Papousek, showed that while the radiant dispersion of the Epsilon Geminids was "of the same order of magnitude as that of the radiants of the individual branches of the Orionids," the fact that the Epsilon Geminids undergo greater planetary perturbations than the Orionids, makes this stream younger. The authors concluded that a relationship between these two streams would be difficult to explain.

The Author has noted some variances in this stream's activity. As noted earlier, the 1960 Russian study remains the only radio-echo survey to detect the Epsilon Geminids, with N1964, S1973, GE1975, and S1976 failing to show a trace. In fact, the activity of this stream has consistently shown signs of being irregular or periodic in nature. The seven known photographic meteors were detected in 1950, 1952 and 1953, with the middle year possessing five of the seven. As pointed out earlier, both Denning and Booth independently observed the shower in 1887, and obtained similar radiants and durations. Finally, Hoffmeister's 12 visual radiants were observed during 1909-1933, but 4 were seen during a three-day interval in 1931.