The duration of this stream extends from March 13-April 17. Maximum occurs over the period of March 31-April 2, from an average radiant of α=285°, δ=+69°. Visual observations reveal low activity from a radiant 2-5° across.
This stream was first recognized in a 1973 study involving 2401 photographic meteor orbits obtained during the Harvard Meteor Project of 1952-1954. The study was conducted by A. F. Cook, B.-A. Lindblad, B. G. Marsden, R. E. McCrosky and A. Posen. They identified four meteor orbits, which formed the “Delta Draconids.” Possessing a duration covering March 28-April 17, the average radiant position was given as RA=281°, DECL=+68°.
Shortly after the above photographic data was published, Zdenek Sekanina published the third paper in his four-part “Statistical Model of Meteor Streams” series. Covering the period of 1961-1965, it listed 72 minor meteor streams, one of which was the “Tau Draconids.” This stream was given a duration of March 24-April 12. The nodal passage came on April 1.7 (λ=11.5°), at which time the radiant position was RA=291.6°, DECL=+71.3°. The last paper of that series was published in 1976 and covered the period of 1968-1969. The Tau Draconids were again detected9this time with a duration extending from March 12-April 12. The date of the nodal passage was given as March 27.0, while the average radiant was RA=286.4°, DECL=+69.1°.
The first visual observations of this shower were actually occurring while Sekanina’s second session of the Radio Meteor Project was in progress. On March 25.92, V. K. Leichenok, N. S. Malikov, L. M. Afanas’eva and T. A. Kopycheva plotted more than 10 meteors from a radiant of RA=280.0°, DECL=+73.0°. The radiant diameter was determined as 5.0°.
As a follow-up to the 1969 observations, the Russian observers strove to confirm the many radiants they had found by conducting another extensive visual survey in 1973. On March 26, S. V. Safonov plotted three meteors from a 1.5 degree diameter radiant at RA=272°, DECL=+72°. During March 27-29, N. V. Smirnov plotted six meteors from a 2.0°-diameter radiant at RA=285°, DECL=+71°.