The duration of this shower extends from December 28 to January 28, with the radiant moving about +1.1° in RA and -0.2° in DECL daily. At maximum on January 8, the shower’s average position is at RA=108°, DECL=+32°. A secondary maximum seems to occur on January 21 from RA=125°, DECL=+25°.
First detection of this stream came during January 1 to 15, 1872, when members of the Italian Meteoric Association plotted 8 meteors from an average radiant of RA=109°, DECL=+34°. W. F. Denning provided the next evidence, when during the period of January 23-24, 1897, he detected meteors from RA=126°, DECL=+19°. C. Hoffmeister gave two radiants in his 1948 book “Meteorströme”. The first radiant was detected on January 14.5, 1921, and was given as RA=109 deg, DECL=+30 deg. The second radiant was detected on January 10, 1931, and was at RA=109°, DECL=+29°. Finally, Opik reported a radiant at RA=107 deg, DECL=+30 deg for the date of January 15-16, 1933.
The first suggestion that a meteor stream might be producing a regular meteor shower from Gemini in mid-January, was made by Richard B. Southworth and Gerald S. Hawkins during 1963. They examined photographic meteor orbits obtained during the Harvard Meteor Program of 1952-1954, and identified 4 meteors as representing the Rho Geminids. They concluded that the shower was active during January 15 to 28 from an average radiant of RA=109.4°, DECL=+32.3°.
Bertil-Anders Lindblad conducted computerized stream searches during 1971. Once again the meteors were from the Harvard Meteor Project of 1952-1954. The most significant search utilized 865 precise meteor orbits and revealed 6 meteors over the period January 15-27 from an average radiant of RA=110°, DECL=+29°.
In addition to visual and photographic detections, the Rho Geminids are also present in two radar surveys. Z. Sekanina recognized this stream during the Radio Meteor Project of 1961-1965. A total of 13 meteors were noted during December 28-January 16. The apparent nodal passage came on January 7.9 (λ=287.0°) the radiant was at RA=108.8°, DECL=+31.5°. Despite the fact that photographic data plainly showed activity to January 27, the radar was not in operation during January 20 to 25, and did not fully cover the period of the shower’s activity during January 17 to 19. However, during the 1968-1969 survey, Sekanina noted 25 meteors during the period January 13-28. The nodal passage came on January 20.8, when the radiant was at RA=125.1°, DECL=+24.9°. On this occasion the radar did not operate during December 21 to January 12, and, although Sekanina named this stream the “January Cancrids,” it seems identical to the Rho Geminids.
The Author’s analysis of the raw orbital data obtained from both sessions of the Radio Meteor Project reveals the stream’s daily motion to be +1.1° in RA and -0.2° in DECL. Although the radiants and orbits of the photographic and radar data are very similar-certainly indicating an association-there seems to be an indication that two distinct populations of meteors exist. Concerning the population of radar meteors, it is interesting that a trend seems to exist which involves a slow decrease in the semimajor axis during the shower’s period of activity.