Tau Capricornids

History

The meteor shower was discovered by Ronald A. McIntosh and was listed in his classic 1935 paper, "An Index to Southern Meteor Showers." McIntosh had isolated ten visual radiants observed by himself and other New Zealand meteor observers which indicated a duration extending from July 10-20. The radiant was noted to move from α=302°, δ=-14° to α=317°, δ=-11°. The shower had been referred to as the "Beta Capricornids II."

One radio-echo survey provides the best evidence for this stream's existence. Zdenek Sekanina analyzed the data accumulated during the 1968-1969 session of the Radio Meteor Project and found the stream's duration to be June 16-July 29. The date of the nodal passage was given as July 12.3 (λ=109.5°), at which time the radiant was at α=310.6°, δ=-14.7°. The orbit was given as follows:

ωΩiqea
311.2109.54.50.2720.7921.310

Curiously, Sekanina gave details of another stream observed during the 1968-1969 session, which he called the "Sigma Capricornids." The duration was given as June 2-July 29. The indicated nodal passage was June 24.3 (λ=92.3°), at which time the radiant was at α=292.4°, δ=-13.6°. The following orbit was given:

ωΩiqea
309.492.38.20.3320.7071.133

The similarity of the two orbits is quite striking (more so than exists between this orbit and that given earlier for the Sigma Capricornids). It is also interesting that these two radio-echo orbits possess many of the same orbital elements as the Northern Iota Aquarids, except that, once again, the ascending node and, thus, the date of maximum is considerably different. As the Tau Capricornids are apparently a minor stream, more will be discussed about its relationship with other streams in the next chapter under the section on the Iota Aquarids.

In recent years, members of the Western Australia Meteor Section have provided some valuable data concerning the rates of this shower. During 1977, meteors were observed over the period of July 12-13. A maximum ZHR of 3.15+/-0.58 occurred on July 13, from α=305°, δ=-10°. Jeff Wood indicates the region is very complex and claims that, in general, a stream the Australian observers refer to as the "Alpha Capricornids" is active during June 16-August 12, with four definite maximums occurring on July 6, 19, 26 and 30. The average radiant is at α=305°, δ=-13°, while the maximum ZHRs range from 5-10 meteors.

A search through the photographic records reveals only one possible member. This meteor was photographed during the Harvard Meteor Project on June 29, 1952. Its radiant was at α=299.3°, δ=-16.1°, while its orbit was given as follows:

ωΩiqea
314.297.67.40.2230.8521.502

No convincing visual evidence exists in the 1899 catalog of W. F. Denning or in C. Hoffmeister's 1948 book Meteorströme, so that this stream might be considered a producer of generally faint, possibly telescopic, meteors.