Taurids

Observing

The Taurids have been identified as a very old meteor stream. There are two branches of the Taurids active during its long duration in the Autumn months (or Spring months in the Southern Hemisphere). The Northern Taurids are active from October 12 to December 2. Maximum is also of long duration and extends over November 4-7 (λ=221-224 deg) from an average radiant of RA=54 deg, DEC=+21 deg. The radiant’s daily motion is +0.78 deg in RA and +0.19 deg in DEC. The Southern Taurids are active during September 17 to November 27. They reach maximum during October 30 to November 7 (λ=216-224 deg) from an average radiant of RA=53 deg, DEC=+12 deg. This radiant’s daily motion is +0.99 deg in RA and +0.28 deg in DEC. Both showers possess maximum hourly rates near 7.

History

The discovery of the Taurids was made in 1869. The Northern Taurids were observed by Giuseppe Zezioli (Bergamo, Italy) during November 1-7, when he plotted 11 meteors from a radiant of RA=56 deg, DEC=+23 deg. The Southern Taurids were observed by T. W. Backhouse (Sunderland, England) on November 6, when 5 meteors were plotted from RA=54 deg, DEC=+14 deg, and possibly by G. L. Tupman (Mediterranean Ocean) on November 12, when 8 meteors were plotted from RA=52 deg, DEC=+12 deg. Although the Southern Taurids were rarely detected during the remainder of the 19th century, the Northern Taurids were frequently observed, but there was one problem–no one was recognizing that an annual shower was being observed from the Taurus region in early November.

It was not until 1918 that the loose ends were finally tied together when Alphonso King (Ashby, England) announced the existence of a new meteor shower. His interest was sparked by the observation of six meteors by T. F. Cranidge and himself within 24 minutes on November 12, 1918. King said the hourly rate for two observers would have been 15, but correcting for bright moonlight would have made this much higher. One additional meteor was seen later in the evening and King’s analysis of the seven plots revealed a radiant of RA=54 deg, DEC=+24 deg. As King was a believer in the stationary radiant theory, his search for previous appearances of this radiant revealed a duration extending from August to December. However, half of the radiants he uncovered occurred during the first half of November.

The Southern Taurids were first discussed in depth in 1920. William F. Denning pointed out that the majority of the “considerable number of fireballs” which appeared in early November of 1920 came from a Taurid shower at RA=59 deg, DEC=+12 deg. He said he had noted the radiant “to have been very active on November 2-3, 1886, when 17 of its meteors were seen at Bristol, and they indicated a diffused radiant situated a few degrees west of the Hyades.”

In the years following 1920, observations of both radiants were fairly abundant, though both were rarely seen by the same observer in the same year. For example, during 1921, J. P. M. Prentice plotted 10 Northern Taurids from a radiant of RA=60 deg, DEC=+22 deg during November 8-10, and A. Grace Cook plotted 11 meteors from RA=63 deg, DEC=+22 deg during November 6-10. However, he detected strong Southern Taurid activity during November 13 and 15, 1922, from RA=53 deg, DEC=+14 deg, and November 2-17, 1923, from RA=54.8 deg, DEC=+11.6 deg. In a 1924 article briefly discussing the Taurid radiants, Denning pointed out that the Southern Taurids (referred to as the Lambda Taurids) exhibited “marked variation in strength in different years.”

In the midst of an ambitious study of 5406 visual radiants, Hoffmeister reexamined the Taurid streams in his 1948 book Meteorstrome. He failed to recognize the Southern Taurids, but he uncovered 91 radiants representing the Northern Taurids. He indicated the stream’s duration to extend from September 27 (solar longitude=183.6) to December 10 (solar longitude=256.9 deg), with the radiant steadily moving from RA=27.2 deg, DEC=+16.8 deg to RA=78.8 deg, DEC=+20.0 deg. Maximum activity was represented by 16 radiants and fell on November 4 (solar longitude=221.9 deg), when the radiant was at RA=51.1 deg, DEC=+21.8 deg. [The Author would like to point out that on page 82 of Hoffmeister’s book, there is a radiant matching the general description of the Southern Taurids. It was based on only 4 visual observations and occurred on November 3 from RA=57 deg, DEC=+8 deg.]

In 1940, Fred L. Whipple commented that the “multiplicity of radiants, the uniformity and the long endurance of the Taurid stream of meteors have disguised its character as one of the more important known showers.”

Although observers and researchers tended to agree with the notion that the region of Taurus and Aries contained several active radiants during October and November, it was the photographic analysis of F. W. Wright and Whipple that made the first elaborate attempt to isolate these. Altogether they found four radiants: Northern Taurids, Southern Taurids, Northern Arietids, and Southern Arietids. The two Arietids streams were not well represented in the data and the authors contemplated that the southern branch might form a continuous stream with the Southern Taurids.

Wright and Whipple’s analysis of the two Taurid streams was quite complete. They found 49 double-station and single-station photographic meteors which represented the Southern Taurids. These indicated a duration extending from October 26 to November 28, and a radiant moving from RA=46.9 deg, DEC=+13.4 deg to RA=67.0 deg, DEC=+16.3 deg. The mean date of photographic activity came on November 8.69, at which time the radiant was at RA=55.2 deg, DEC=+14.5 deg. The 24 double-station and single-station meteors representing the Northern Taurids revealed a duration of October 17-December 1, with the radiant moving from RA=44.6 deg, DEC=+19.0 deg to RA=67.5 deg, DEC=24.5 deg. The mean date of photographic activity came on November 10.72 from a radiant of RA=56.9 deg, DEC=+22.4 deg. The authors said the hourly rate of the Southern Taurids seemed to rise abruptly to an early November maximum, slowly decline, and then rise again to a secondary maximum on November 11, while the Northern Taurids showed only a flat maximum around mid-November. They concluded that the differences and character of the activity of the two streams indicated the Southern Taurids were less diffuse than the northern branch and, therefore, may have developed more recently.

Other photographic surveys were conducted during the 1950’s and 1960’s by astronomers in both the United States and the Soviet Union. The subsequent analyses of these photographic meteor orbits tended to reveal similar orbital details, but the utilization of fewer meteors did not allow a determination of the radiant, date of maximum and daily motion that could compare with that of Wright and Whipple. The Author has combined the double-station photographic orbits obtained from all of these surveys and has produced orbits for both Taurid streams (see “Orbit” section). However, the data is still inadequate to enable an accurate determination of even the date of maximum. The reason for this is that photographic Taurids are in greater abundance in October than in November. Whether this is due to mass distribution within the streams or just an inadequate use of cameras during November can not be determined at this time. The Author has, however, determined the daily motion of both Taurid radiants, with values of +0.78 deg in RA and +0.19 deg in DEC being determined for the northern stream, and +0.99 deg in RA and +0.28 deg in DEC being determined for the southern stream.

Radio-echo studies became a powerful addition to the arsenal of astronomers in the mid-1940’s. Unfortunately, even the best equipment then available, which was located at Jodrell Bank, possessed a resolution so low it was impossible to separate the two Taurid streams. Thus, from 1946 to 1958 radio-echo details revealed only a general picture of the Taurid shower. For 1946 and 1947, not even a radiant could be determined, but radio-echo rates of 18 per hour were detected on November 9 of the former year, while rates reached 9 per hour on November 6 of the latter year. In 1950, 109 echoes were detected on November 9, which revealed a radiant of RA=55 deg, DEC=+25 deg. The maximum hourly rate reached 14.

For the period of 1951-1953, the Jodrell Bank survey obtained four radiant determinations. In 1951, 57 echoes detected on November 7, revealed a 4 degree-diameter radiant of RA=61 deg, DEC=+25 deg, while the maximum hourly rate reached 25. Two radiants were detected in 1952. The first was a 3 degree-diameter radiant located at RA=52 deg, DEC=+24 deg on November 5, while the second was a 6 degree-diameter radiant located at RA=59 deg, DEC=+17 deg on November 10. The maximum hourly rates attained 7 and 14, respectively. In 1953, a 3 degree-diameter radiant was detected at RA=58 deg, DEC=+25 deg on November 9. The maximum hourly rate reached 8. The additional survey years of 1954-1958 closely reflected the results obtained during 1950-1953.

As the 1960’s began, radio equipment had been set up in other areas of the world—equipment which was more sensitive than that at Jodrell Bank. For the first time, astronomers had the means to precisely detect meteors at magnitudes fainter than what photographic methods offered. During 1960, B. L. Kashcheyev and V. N. Lebedinets (Kharkov Polytechnical Institute, USSR) succeeded in splitting the Taurids into two distinct streams, despite the fact that the equipment did not operate beyond October 23. Southern Taurids were detected during September 20-October 22, during which time 73 meteors were detected from an average radiant of RA=27.2 deg, DEC=+8.6 deg. The Northern Taurids were detected during October 11-23, during which time 13 meteors were detected from an average radiant of RA=33.5 deg, DEC=+18.2 deg. The authors determined orbits for each stream, based on velocity measurements, and concluded that both streams were in good agreement with the orbits determined by photographic methods.

The next step in the evolution of radio equipment possessed the capability of detecting meteors far below naked-eye visibility. They uncovered a very interesting bit of information on the Taurid stream: the orbital planes of the northern and southern streams were so similar at this level, computer analysis was unable to distinguish a difference between the two streams. Zdenek Sekanina, director of the Radio Meteor Project of the 1960’s, noted, “The gap between the two branches, so striking in the case of bright photographic meteors, is no longer seen in the radio sample. Also, the radio Taurids appearing on the same day as the bright photographic Taurids have their radiants, on an average, shifted eastward.” Sekanina said the most notable difference in the orbital elements was in the longitude of perihelion, which varied from the photographic orbits by nearly 10 deg. He concluded that the separation between the photographic and radio data “may suggest a difference in the mean age between the two groups of meteors.”

With observations of both Taurid radiants becoming more numerous as the 20th century progressed, certain facts about the streams became known. Two of the most notable characteristics were the long durations and the slow daily motion of each streams’ radiant. This led to the 1930s conclusions of O. Knopf and Cuno Hoffmeister that the Taurids were of interstellar origin rather than a product of the solar system. This conclusion was challenged in 1940, when Fred L. Whipple published a list of fourteen photographic meteors detected by the northern stations of Harvard Observatory during 1937-1938. Orbits were computed for six of the meteors simultaneously photographed by two cameras, and this allowed Whipple to discover that the Taurids possessed unusually short periods. He concluded that the semimajor axis, eccentricity and longitude of perihelion all pointed to a possible association with periodic comet Encke, and that the observed 10 deg-15 deg difference in the planes of the meteor orbits and the comet could be explained as the result of 14,000 years worth of perturbations from Jupiter.

The origin of the Taurids was reexamined by Whipple and S. Hamid during 1950. They calculated the effects of secular perturbations by Jupiter on the orbital inclination and longitude of perihelion of nine photographic meteor orbits and found the orbital planes of four of the meteors to coincide with that of comet Encke 4700 years ago. Three other orbits coincided with one another, but not with comet Encke 1500 years ago. The authors theorized “that the Taurid streams were formed chiefly by a violent ejection of material from Encke’s Comet some 4700 years ago, but also by another ejection some 1500 years ago, from a body moving in an orbit of similar shape and longitude of perihelion but somewhat greater aphelion distance….” It was suggested that this unknown body had separated from Encke some time in the past.

Whipple’s 1940 paper discussed more than the Taurids and their link to comet Encke. He said the stream’s apparent spread of 0.2 AU meant Mercury, Venus and Mars were also likely to encounter it. He also noted that the stream could produce a post-perihelion shower for Earth which would occur in late June and early July during daylight. Of course it will be some time before the “Taurids” of Mercury, Venus and Mars are confirmed, but, in 1951, Mary Almond computed orbits for the daylight streams discovered at Jodrell Bank and found the Beta Taurids of June to be very similar to the Northern Taurids.

I. S. Astapovich and A. K. Terent’eva conducted a study of fireballs appearing between the 1st and 15th centuries and revealed the Taurids to have been “the most powerful shower of the year in the 11th century (with 42 fireballs belonging to them) and no shower, not even the great ones, could be compared with them as to activity.” The authors said both branches of the stream were active: the Northern Taurids possessed a duration of October 20-November 18, with an average radiant of RA=56 deg, DEC=+24 deg, while the Southern Taurids had a duration of October 25-November 17 and an average radiant of RA=54 deg, DEC=+8 deg. The northern stream was the strongest of the two branches and possessed a radiant measuring 6 degx1 deg. The southern shower was only half as active as the northern and possessed a radiant 3° in diameter. The existence of the Taurid streams cannot be accounted for between the 11th and 19th centuries.

The Taurids took on a new importance in 1978 when L. Kresak suggested the Taurid parent body, comet Encke, might be related to the Tunguska object of 1908. The Tunguska object came down over Siberia in 1908 leaving a trail of dust across the sky and exploded above the ground leveling about 2150 square kilometers of forest. Although Z. Sekanina disputed the possibility of such a link in 1983, the idea was renewed during the early 1990s by Duncan Steele, D. J. Asher, and Victor Clube. Because of the latter three astronomers, the Taurids are now referred to as the Taurid Meteoroid Complex and, more commonly, the Taurid Complex.

Visual details of the Taurid meteors have not been lacking during the last two decades, though it is unfortunate that the two streams are rarely separated due to their closeness to one another. With astronomers attempting to estimate the ages of the northern and southern branches, it would be especially interesting to compare the characteristics of the respective meteor populations. The only recent attempt to visually separate the northern and southern streams came in 1983, when members of the AK Meteore (East Germany) observed 40 Southern Taurids and 69 Northern Taurids. The first stream was detected during September 26-December 3, with the average magnitude being estimated as 4.25, while the second stream was seen during September 26-December 4, with an average magnitude of 3.87. Although the average magnitudes are unusually low (due to very favorable observing conditions), the difference between these values seems significant and, of course, implies that the Southern Taurids possess a fainter population of meteors than the northern branch. Support or denial of such a statement will, however, require additional observations. Meanwhile, researchers must be content with visual details on the Taurid stream as a whole, as given in the following table.

Taurid Magnitudes and Trains

Observers in the previous table were Norman W. McLeod, III (Florida), Felix Martinez (Florida), Bert Matous (Missouri), Western Australia Meteor Section, Koen Miskotte (The Netherlands), Paul Roggemans (Belgium), 15 observers in Finland, Trond Erik Hillestad (Norway).

Estimates of the hourly rates of the Taurids reveal fairly weak activity which hardly allows the shower to stand out among the other active showers and the usual numbers of sporadic meteors. In 1980, Norman W. McLeod, III (Florida) saw the highest hourly rates reach 5-8 for the Southern Taurids and 2-4 for the Northern Taurids during November 5-7. That same year, members of the Western Australia Meteor Section found the Southern Taurids to reach a maximum ZHR of 14.21+/-1.89 on November 6, while the Northern Taurids reached a maximum of 6.57+/-1.15 on November 10. Members of AK Meteore (East Germany) observed the Taurids during 1983. According to Jurgen Rendtel, they noted the Southern Taurids to have began October with ZHRs around 2. This rate persisted until around October 20, when the ZHR climbed to over 3. After a maximum ZHR of about 4 was attained during October 27-November 9, activity levels quickly dropped to around 2 following November 11. For the Northern Taurids, the 1983 ZHR levels were typically between 2-4 from October 1 to December 4. A maximum ZHR of 4-6 came during October 27-November 9.

The Western Australia Meteor Section has provided excellent determinations of the color of the Taurid meteors in recent years. During 1983, 206 meteors were observed, with the predominant colors being determined as white (46.7%) and yellow (44.0%). Other observed colors included orange (5.3%), blue (2.7%) and green (1.3%). In 1978, they reported yellow and blue-green percentages of 33.1% and 6.3%, respectively, while observations in 1979 revealed yellow and orange percentages of 23.2% and 4.3%, respectively.