(Image produced by the Author using Starry Night 2.0 and Adobe Photoshop 5.0. It represents the view from mid-northern latitudes at about 8:30 p.m. local time around October 8.)
Draconids ("Giacobinids")
Best Night: October 9-10, with 1-2
meteors per hour (with occasional outbursts of hundreds to
thousands)
Total Duration of Activity: October 6-10
The point from where the Draconid meteors appear to radiate is located within the constellation Draco and is referred to as the radiant. The radiant is located near the head of Draco. The exact location of the radiant in astronomical terms is RA=262° (17 hours 28 minutes), DEC=+54°, but the following chart will also help you find it.
(Image produced by the Author using Starry Night 2.0 and Adobe
Photoshop 5.0. It represents the view from mid-northern latitudes
at about 8:30 p.m. local time around October 8.)
To best observe the Draconids
wear appropriate clothing for the weather. Lay outside in a
reclining lawn chair with your feet pointing towards the east or
northeast. Do not look directly at the radiant, because meteors
directly in front of you will not move much and fainter ones
might be missed. Instead, keep your center of gaze about 30 or 40
degrees southeast of the radiant. When you see a meteor mentally
trace it backwards and if you arrive at the "head" of
Draco it is probably a Draconid.
The discovery of this meteor
shower resulted from predictions by several astronomers that the
periodic comet Giacobini-Zinner might produce a radiant in early
October.
The first to make such a
prediction was the Reverend M. Davidson, who, in 1915, examined
the periodic comets observed since 1892 to isolate any that might
be capable of producing meteor showers. One of the comets which
met the established criteria was Giacobini-Zinner. Davidson found
that the comet's orbit would be fairly close to Earth on October
10, 1915, and predicted that, if the debris from this comet had
spread outward by about two million miles, a shower might be
active from RA=267°, DEC=+50°. This was about two years after
the parent comet had passed perihelion. During the first half of
October, William F. Denning recorded "a number of
meteors" from RA=267°, DEC=+49°.
Davidson revised his prediction in
1920 (primarily due to a discovered error in his earlier
prediction), saying that the distance between the orbits of the
comet and Earth amounted to 5 1/2 million miles. He subsequently
suggested that maximum would most likely occur on October 9 from
RA=251.5°, DEC=+55.9°. Later that same year, Denning became the
first observer to make a definite observation of this new shower,
as he observed 5 meteors from RA=268°, DEC=+53° during October
6-9. These meteors were described as slow. Giacobini-Zinner had
passed perihelion during the Spring of 1920.
The comet was next expected at
perihelion at the end of 1926, and predictions for a meteor
shower in October of that year were made by both Davidson and A.
C. D. Crommelin. Both men gave October 10 as the expected day of
maximum, and they gave similar radiants of RA=261°, DEC=+53.5°
and RA=265°, DEC=+54°, respectively. The orbits of the comet
and Earth were found to intersect in 1926, though the expected
shower would occur 70 days before the comet passed that point of
its orbit. Around October 10.4, observers in England were made
aware that some unusual activity was present.
What gained the attention of many
observers on October 9, 1926, was the appearance of a fireball.
The event was noted by hundreds in the British Isles and 35
reports allowed the radiant to be determined as RA=262°,
DEC=+55°. The meteor moved slowly and lit up the sky. A
persistent train lasted about 30 minutes "during which time
it underwent curious changes of form and exhibited drift amongst
the stars."
Several other radiants were
determined in 1926, which acted to confirm the predictions of
Davidson and Crommelin. J. P. M. Prentice (Stowmarket, England)
observed for 3 hours centered on October 9.9, and detected 16
meteors from RA=263°, DEC=+54°. He described the meteors as
slow and estimated the radiant diameter as 6 deg. He claimed that
the hourly rate may have been near 17 had his observations been
continuous. Observations made by Alphonso King (Ashby) and
Denning (Bristol) gave a radiant of RA=255°, DEC=+56°.
The years following 1926 were
closely monitored by a few observers trying to catch another
glimpse of the Draconid shower. During 1927-1932, Prentice
observed extensively around October 9-10, but no activity was
detected.
Comet Giacobini-Zinner passed perihelion on July 15, 1933, and, at the time of the predicted maximum of October 9, Earth crossed the area of the comet's descending node just 80 days after the comet. Astronomers were not prepared for what was in store for them, but, as evening twilight fell over Europe, observers noted the beginnings of something unusual. Within just a couple of hours the number of Draconids skyrocketed, and, at 20:00 UT, one of the best displays of the 20th century was in progress. Some of the more impressive statistics follow:
As can be gathered from these
reports (and many others not included here), the shower's maximum
rate reached 100 per minute, or about 6000 per hour, around 20:15
UT on October 9. The meteors were slow, generally faint and were
usually yellow.
Following the 1933 appearance, the
Draconids again fell to nonexistence. The comet's next perihelion
date was February 17, 1940, and there were numerous predictions
of a possible strong return in October 1939. However, Earth
crossed the comet's orbit 136 days ahead of the comet which meant
bad news for meteor enthusiasts, as no storm---or even a small
shower---appeared.
During 1940 to 1945, activity
continued to be absent, but astronomers were already making
predictions for the very favorable 1946 return. In that year, the
comet was expected at perihelion on September 18, so that Earth
would cross the comet's orbit just 15 days after the comet!
The Draconids were best placed for
observers in the Western Hemisphere during October 9/10, with
excellent meteor counts not only coming from all across the
United States, but Canada and even Venezuela. European observers
did detect the Draconids, but the radiant was very low over the
horizon and, though spectacular, it was at least one-fourth the
strength of that seen in America. Observations were also made in
Czechoslovakia for slightly more than one hour prior to morning
twilight. Some of the more interesting observations are as
follows:
What may have been the
highlight of this event was the appearance of a large blue-white
fireball over Southern California at 3:38 UT. Forsyth said it
left a yellow train which lasted over three minutes. As the train
drifted and became diffuse, it took on the shape of a horseshoe.
The 1946 event marked an important
first for meteor astronomy---the detection of a meteor shower by
radar. In the United States alone, 21 radar systems were operated
at frequencies of 100, 600, 1200, 3000 and 10000 Mc/sec. From
these instruments only the radar operating at 100 Mc/sec detected
meteor echoes. The majority of all meteor activity occurred
between 3:00 and 4:30 UT on October 10. Other radar equipment
operating in London and the Soviet Union operated at frequencies
between 3.5 Mc/sec and 212 Mc/sec and confirmed that maximum
occurred between 3:00 and 4:00. Most interesting was a record
obtained by J. A. Pierce, who used a 3.5 Mc/sec pulsed
ionospheric sounder and found that meteors were so numerous that
a temporary ionosphere was formed at a height of 90 km. The
meteoric ionosphere lasted three hours and was confirmed
elsewhere.
Following 1946, both visual and
radio-echo techniques were utilized in searches for this shower
during 1947-1951. Visual observers detected no meteors possibly
associated with the Draconids, while radio-echo observations at
Jodrell Bank detected "no activity during the Giacobinid
epoch in excess of the background sporadic rate (that is, not
greater than 4 or 5 per hour)."
A possible shower was predicted
for October 9, 1952. Various calculations revealed Earth would
cross the comet's orbit 193 days ahead of the comet. In addition,
the closest distance between the orbits of Earth and
Giacobini-Zinner was very similar to that of 1933, or about
0.0057 AU; however, on this occasion, the comet's orbit would
actually pass inside of Earth's orbit. Visual observations by
British observers revealed only the barest hint of activity
shortly after sunset on October 9/10, but, just a few hours
earlier, daylight observations had been made using the radio-echo
apparatus at Jodrell Bank in England.
The Jodrell Bank team first noted
the Draconid rate rising above that of the sporadic background at
14:20 UT on October 9. Meteor echoes were counted during
10-minute intervals: 3 were noted at 15:00, there were 6 at
15:10, 10 at 15:20, 11 at 15:30 and 17 appeared at 15:40. The
highest rates occurred at 15:50, when a 10-minute rate of 29 was
reported---indicating an hourly rate of 174. The following
decline in activity was very rapid, and one-half hour after
maximum the 10-minute rate had declined to only 3. The last
definite sign of activity occurred at 16:40, when the rate was 2.
The Jodrell Bank observers concluded that maximum occurred at a
solar longitude of 196.25 deg from RA=262 deg, DEC=+54 deg.
The 1959 return of
Giacobini-Zinner was very favorable and, since Earth arrived at
the comet's orbit just 21.6 days before the comet passed through
the region some believed a meteor storm would occur. However, the
comet's perihelion distance had been pulled closer to the sun so
that the closest distance between the orbits of Earth and the
comet was 0.058 AU. Subsequently, no shower was observed. The
comet's 1966 return also failed to produce meteors due to
unfavorable geometric conditions.
Giacobini-Zinner passed only 0.58
AU from Jupiter during 1969, which acted to increase its
perihelion distance to 0.99 AU---Draconid showers were again
possible. Searches for activity began during October 1971, with
Earth crossing the comet's orbit 309 days before the comet. No
notable activity was observed during October 7 to 10, by members
of the American Meteor Society, as hourly rates remained around
one.
The 1972 Draconids were looked
for with much anticipation. Not only was Earth going to cross the
comet's orbit 58.5 days after the comet, but the two orbits were
separated by only 0.00074 AU! Unfortunately, despite these
promising statistics, the shower was quite a disappointment.
Observers in the United States obtained the highest visual rates
when 10-15 per hour were detected on October 8/9. Maximum had
been predicted for 17:00 UT on October 8, which made Japan the
best location for observations. Unfortunately, the Japanese
observers were met with cloudy skies. Despite this hindrance, the
Hiraiso Branch of the Radio Research Laboratory operated a 27.1
MHz radar. A peak of 84 returns in 10 minutes was noticed at
16:10 UT on October 8, followed by a secondary peak of 69 returns
in 10 minutes at 21:00 UT. Further predictions for Draconid
showers in 1978-1979 and 1985-1986, were not met with noticeable
displays.
Predictions were published in
every major astronomy publication telling of the possibility of
an outburst of the Draconids. Although it was difficult to pin
down the exact time of maximum, the generally accepted time was
expected to be around 1921 hours universal time on October 8,
which was around the time Earth would be crossing closest to the
orbit of comet Giacobini-Zinner. Interestingly, previous displays
of the Draconids indicated the outburst could occur as early as
17 hours UT on the 8th or as late as 12 hours UT on the 10th. In
this year, the possibility existed that the full activity curve
of the Draconids would be mapped out for the first time ever, not
only because of a very active worldwide network of visual
observers covering the night sky, but also because of the
numerous professional and amateur radio systems in operation
designed to tabulate meteor echos during both nighttime and
daytime hours.
Activity was normal on October 7
and during most of the first half of October 8, but a number of
hours before any activity was expected, visual observations in
China indicated the Draconids were coming to life.
Jin Zhu (Beijing Astronomical
Observatory) was observing with friends Yaohua Li, Xiaosong Liu,
Xiangyang Li, Xiaoming Teng, and Xianzhong Zheng beginning at
11:43 UT on October 8. Sky conditions were not good, with the
limiting magnitude being estimated as 4.2. Observations continued
until 12:27 UT, when moonlight and clouds almost completely
degraded the already poor conditions. Jin Zhu reported he saw 26
Draconids during that period, while an additional 12 were noted
by his friends.
Hashimoto Takema (Japan) reports
that several observers detected high visual rates on the 8th.
They indicate a peak of over 100 per hour was noted between 13:00
and 14:00 UT. Even more interesting is that the moon was then
above the horizon!
Petr Pridal was operating the
radar backscatter equipment at Ondrejov Observatory (Czech
Republic), which enabled observations during both night and day.
Rates had been normal for several hours, but between 11 and 12
hours UT the normal hourly meteor rates of about 80 jumped to
about 140. Hourly rates continued to increase to about 340 during
12-13 hours UT. Rates peaked at about 500 per hour during 13-14
hours UT, and then dropped to near 330 during 14-15 hours UT, 180
during 15-16 hours UT and 100 at 17-18 hours UT. Rates had
returned to normal thereafter.
Interestingly, Werfried Kuneth
(Austria) began monitoring VHF TV-carriers signals at 53.760 and
62.250 Mhz at 13:20 UT to watch for the Draconids. He noted rates
were already higher than when he had temporarily shut down at
11:30 UT. He said the activity rates aparently peaked at 13:40 UT
and then declined. By 15:00 UT the Draconids were apparently
gone.
As nighttime fell across Europe,
the visual display had greatly subsided, with experienced
observers typically giving hourly rates of 3 to 7.
Overall, the Chinese and Europeans
indicate the Draconids were rich in faint meteors, with visual
observers generally indicating most meteors were in the 3rd to
4th magnitude range. (None of the European observers reported
meteors brighter than magnitude 2.)
During the two sessions of the Radio Meteor Project, which was conducted during the 1960's, Zdenek Sekanina isolated enough meteors for the following two orbits to be determined:
| AOP | AN | i | q | e | a | |
|---|---|---|---|---|---|---|
| S1970 | 184.0 | 192.2 | 51.5 | 0.997 | 0.623 | 2.647 |
| S1976 | 187.6 | 194.5 | 49.2 | 0.994 | 0.553 | 2.221 |
C&MS Home | Calendar | Meteor Information | Meteor WWW Links | Glossary
If you have any questions, please email me