The duration of this shower extends from December 28 to January 28, with the
radiant moving about +1.1 deg in RA and -0.2 deg in DECL daily. At maximum on
January 8, the shower's average position is at RA=108 deg, DECL=+32 deg. A
secondary maximum seems to occur on January 21 from RA=125 deg, DECL=+25
deg.
History
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 deg, DECL=+34 deg. Denning provided the next evidence, when
during the period of January 23-24, 1897, he detected meteors from RA=126 deg,
DECL=+19 deg. Cuno Hoffmeister gives two radiants in his 1948 book Meteorstrome.
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 deg, DECL=+29 deg. 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 deg, DECL=+32.3 deg.
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 deg,
DECL=+29 deg.
In addition to visual and photographic detections, the Rho Geminids are also
present in two radar surveys. Zdenek 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 (Solar
Longitude=287.0 deg) the radiant was at RA=108.8 deg, DECL=+31.5 deg. 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 deg, DECL=+24.9
deg. 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, as can be seen in the "Orbit" section below.
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 deg in RA
and -0.2 deg 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.