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 (solar longitude=221 deg-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
(solar longitude=216 deg-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.
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 deg 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.
Year(s) | Ave. Mag. | # Meteors | % Trains | Observer(s) | Source |
---|---|---|---|---|---|
1976 | 2.72 | --- | 1.3 | McLeod | MN, No. 36 |
1976 | 3.47 | --- | 2.0 | Martinez | MN, No. 36 |
1976 | 2.44 | --- | 3.4 | Matous | MN, No. 36 |
1978 | 2.33 | 284 | 10.9 | WAMS | MN, No. 45 |
1983 | 2.92 | 206 | 4.4 | WAMS | WGN, 12, No. 3 |
1984 | 2.89 | 75 | 4.0 | Miskotte | WGN, 13, No. 1 |
1985 | 2.27 | --- | 4.2 | WAMS | MET, 16, No. 4 |
1985 | 2.93 | 59 | --- | Roggemans | WGN, 13, No. 6 |
1985 | 2.76 | 83 | 6.0 | Finland | WGN, 14, No. 2 |
1985 | 3.46 | 50 | --- | Hillestad | WGN, 14, No. 2 |
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.
The following orbits were determined by the Author using photographic meteors collected from W1954, MP1961, B1963 and BK1967. The Northern Taurids are based on 20 meteors, while the Southern Taurids are based on 25.
AOP | AN | i | q | e | a | |
---|---|---|---|---|---|---|
N. Taurids | 295.6 | 224.2 | 3.2 | 0.343 | 0.843 | 2.186 |
S. Taurids | 114.3 | 27.3 | 5.0 | 0.370 | 0.806 | 1.910 |
During 1960, Kashcheyev and Lebedinets operated radio-echo equipment at the Kharkov Polytechnical Institute (USSR) and established the following orbits for the northern and southern branches of the Taurid stream. Since the equipment was not operated after October 23 (thus missing the maximum of each stream) the values given for the ascending nodes are probably considerably smaller than they should be.
AOP | AN | i | q | e | a | |
---|---|---|---|---|---|---|
N. Taurids | 294.6 | 205.4 | 5.5 | 0.36 | 0.84 | 2.17 |
S. Taurids | 118.2 | 14.6 | 2.2 | 0.33 | 0.84 | 2.08 |
As noted earlier, the northern and southern streams were not separated by the very sensitive radio-echo surveys of the Radio Meteor Project. Thus, the following orbits should be considered as averages for the Taurid stream as a whole.
AOP | AN | i | q | e | a | |
---|---|---|---|---|---|---|
S1970 | 114.1 | 49.7 | 1.4 | 0.385 | 0.770 | 1.679 |
S1976 | 293.6 | 217.2 | 0.0 | 0.398 | 0.750 | 1.596 |
As can be seen, it could be possible to argue
that the southern stream had the greater influence on the first orbit, while the
second orbit was influenced for the northern stream.
The orbits of comet Encke and the Beta Taurids are
given here for comparison. The orbit of the Beta Taurids
comes from S1973.
AOP | AN | i | q | e | a | |
---|---|---|---|---|---|---|
Encke | 186.0 | 334.2 | 11.9 | 0.340 | 0.847 | 2.218 |
Beta Taurids | 239.2 | 274.5 | 0.3 | 0.274 | 0.834 | 1.653 |
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