The first sighting of this meteor shower seems
to be linked to observations by William F. Denning during 1916 and 1917. During
the former date, 4 meteors were seen over the period of October 20 to 25, from a
radiant at RA=28 deg, DEC=+4 deg. The meteors were described as rapid. On
October 16, 1917, a 1st-magnitude stationary meteor was observed from RA=28 deg,
DEC=+3 deg.
Other observations are hard to
come by in the records of visual radiants; however, four radio-echo surveys may
have detected this stream during the 1960's. Using the radio equipment at
Adelaide Observatory (South Australia) in 1961, C. S. Nilsson detected stream
members during October 23-30. Although the data revealed a nodal passage on
October 27 (solar longitude=213.9 deg) and an average radiant of RA=39.3 deg,
DEC=+0.2 deg, the equipment did not operate during September 30-October 19, so
that the early part of the shower's activity was missed. During the 1961-1965
session of the Radio Meteor Project, Zdenek Sekanina isolated a stream which he
called the "Beta Cetids." The stream possessed a duration extending from
September 8 to October 1. Its nodal passage was given as September 25.7 (solar
longitude=182.2 deg), while the average radiant was RA=16.3 deg, DEC=11.7
deg. The second session of the Radio Meteor Project detected a possibly
associated stream during September 22-October 22, 1969. The apparent date of the
nodal passage was October 5.2 (solar longitude=191.6 deg), at which time the
radiant was at RA=12.5 deg, DEC=+4.2 deg. This stream was called the "Delta
Piscids." Finally, G. Gartrell and W. G. Elford operated radio equipment at
Adelaide Observatory during October 15-19, 1969. Although the indicated nodal
passage came on October 16 (solar longitude=203 deg) from RA=28 deg, DEC=+3 deg,
the equipment had been shut down since mid-June, so that the early part of the
activity was definitely missed. The orbits revealed by each of these surveys (in
order of their discussion above) are as follows:
AOP | AN | i | q | e | a | |
---|---|---|---|---|---|---|
1961 | 94.0 | 33.9 | 13.9 | 0.52 | 0.86 | 3.70 |
1961-1965 | 102.4 | 2.2 | 14.6 | 0.493 | 0.725 | 1.792 |
1969 | 93.6 | 11.6 | 0.7 | 0.566 | 0.693 | 1.843 |
1969 | 96 | 23 | 8.2 | 0.47 | 0.90 | 4.17 |
As previously noted, the data published in
N1964 and GE1975 did not cover the early half of this stream's activity, thus
giving the indicated nodal passages little meaning. In addition, the orbits from
these two surveys were each based on only three meteors, so that the reliability
should not be considered very high.
The
orbits obtained in each of Sekanina's surveys should be considered more
reliable, as they were based on about 10 and 45 meteors, respectively. Most
interesting is the inclination change between the 1961-1965 and 1968-1969
surveys, but this may be a result of the different selection methods being used:
the early study used a D-criterion of 0.20, while the second survey used a less
stringent value of 0.25. After obtaining the 39,145 radio meteor orbits computed
by Sekanina during the 1960's, the Author has found 57 meteors that are probable
members of this stream. Combined with 13 photographic meteors found in MP1961
and C1977, the subsequent orbit was obtained:
AOP | AN | i | q | e | a |
---|---|---|---|---|---|
95.4 | 15.2 | 7.3 | 0.529 | 0.745 | 2.075 |
By utilizing a D-criterion value of about 0.15, the Author finds that this stream splits into northern and southern branches. The fairly compact northern branch was composed of 46 radio and photographic meteors, while the more diffuse southern stream was composed of 16 meteors.
AOP | AN | i | q | e | a | |
---|---|---|---|---|---|---|
Northern | 95.4 | 16.2 | 4.2 | 0.537 | 0.740 | 2.065 |
Southern | 96.0 | 13.6 | 13.6 | 0.528 | 0.744 | 2.063 |
The northern branch is definitely the strongest portion of this stream, but neither branch is especially strong visually and the Author believes telescopic aid will probably be necessary for future observations. What makes this stream especially interesting is its orbital similarity to the lost Apollo asteroid Hermes (1937 UB).
AOP | AN | i | q | e | a | |
---|---|---|---|---|---|---|
Hermes | 90.7 | 35.3 | 6.2 | 0.617 | 0.624 | 1.639 |
This asteroid's ascending node occurs around
October 29, which coincides with the end of the October Cetid shower.
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