Beta Taurids

Observing

This daylight shower is active during June 5 to July 18. It exhibits a relatively flat maximum centered on June 29 (λ=98.3 deg), that originates from an average radiant of RA=79.4 deg, DECL=+21.2 deg. The maximum hourly rate reaches about 25 to the eyes of radar, and the normally 3 deg diameter radiant suddenly swells to at least 7 deg around July 2.

History

This shower was first detected by Jodrell Bank observers during June 20-27, 1947, from a radiant near RA=79 deg to 85 deg, DECL=+20 deg to +30 deg. The activity rate ranged from 20 to 30 radio meteors per hour. Apparent confirmation of this stream came during June 24 to July 4, 1948, when the average radiant was determined as RA=90 deg, DECL=+26 deg and the hourly rate reached a high of 35 on July 3. These radio-echo studies were of a fairly low precision and, although the Beta Taurids were detected, it was not until 1950, that more precise details of the stream became available.

During June 26 to July 4, 1950, the Jodrell Bank equipment again found the Beta Taurids, this time at an average radiant of RA=86.2 deg, DECL=+18.7 deg. Researchers analysing the data concluded that maximum activity occurred on July 2 (Solar Longitude=99 deg) and that the radiant seemed to move "at random from day to day in an area of sky 8 deg x 14 deg in Taurus." The daily radiants of this stream remained less than 3 deg across until July 2 and 3, when the radiant diameter was 7 deg and 5 deg, respectively. The diameter was again less than 3 deg across on July 4. These same observations were also used to determine the first orbit for this stream, which indicated a semimajor axis of 2.2 AU, a perihelion distance of 0.34 AU and an inclination of 6 deg.

Radar observations continued at Jodrell Bank during the next several years. From observations obtained during the period 1950 to 1952, Mary Almond, K. Bullough and Gerald S. Hawkins established the mean daily motion as +0.8 deg in RA and +0.4 deg in DECL. In 1954, Bullough determined more refined details of the shower by adding observations made in 1953. The daily motion was given as +0.67 deg in RA and +0.44 deg in DECL. He described the Beta Taurids as "a rather weak stream with no peak of activity. The shower is active for about a week centred on a sun's longitude of 97 deg to 98 deg." Curiously, the 1953 data revealed a radiant diameter of 3 deg to 4 deg throughout the time of activity until July 2, when it increased to 8 deg. Finally, after 1958 studies had been conducted, G. C. Evans analysed the Jodrell Bank radar studies made between 1950 and 1958 and concluded that maximum came when the solar longitude was 97.7 deg, and that the average radiant was then RA=85.4 deg, DECL=+19.4 deg. The daily motion was determined to have averaged +0.57 deg+/-0.12 deg in RA and +0.16 deg+/-0.22 deg in DECL. Evans described the shower maximum as "rather weak and broad."

The Beta Taurids were also detected from the Southern Hemisphere during 1953. C. D. Ellyett and K. W. Roth delineated 21 shower radiants while using radar equipment at Christchurch, New Zealand. Shower number 10 was detected during the period of June 17-26. The radiant ranged from 82 deg to 85 deg in RA and +20 deg to +25 deg in DECL. The mean radiant was given as RA=84 deg, DECL=+23 deg.

During 1961, this stream was detected by C. S. Nilsson, while operating radar equipment at Adelaide Observatory in Australia. Only 7 meteors were found, but the equipment was not in operation after June 19, so that this observation was that of the early part of the shower. The duration was June 12 to 18, and the radiant was at RA=75.5 deg, DECL=+20.3 deg. Nilsson pointed out that his data showed significant correlations between both the radiant position and geocentric velocity with time. He added that the "sign of the mean heliocentric latitude...is not significant, so the node marked as ascending is quite possibly a descending node, for at least part of the stream."

It was not until the studies of the Radio Meteor Project, at Havana, Illinois, that the true extent of the Beta Taurids became known. Zdenek Sekanina, director of the project, found that the 1961-1965 data indicated a duration extending from June 12 to July 6, while the 1968-1969 data revealed a duration extending from June 5 to July 18. The first study revealed an orbit similar to those reported previously, while the second study showed both the argument of perihelion and ascending node shifted by 180 deg---adding further strength to Nilsson's observation that some of the stream's orbit might be at its descending node when crossing Earth's orbit during June and July.

Strong evidence seems to exist indicating the Beta Taurids are the same stream, or at least closely related to the stream, that later produces the Taurids during October and November. The suggestion was first made in 1951, by Mary Almond and has since been supported on numerous occasions by Nilsson, Sekanina and others. In 1964, Nilsson noted that the correlation of radiant position and geocentric velocity with time was also present during the duration of the Taurids. Other researchers have pointed fingers at the stream's long duration, flat maximum and diffuse radiant as other characteristics previously noted in the Taurids. The Taurids are believed to be a very old remnant of periodic comet Encke---the current record holder for having the shortest period.

It should be noted that the suggestion that the Taurids might produce a shower visible during the daylight hours of summer was first mentioned during 1940 by Fred L. Whipple.