Smithsonian

Contributions to Astrophysics

VOLUME 3, NUMBER 8

METEOR TRAINS

by ROBERT F. HUGHES

SMITHSONIAN INSTITUTION

Washington, D.C.

1959

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Publications of the Astro physical Observatory

This series, Smithsonian Contributions to Astrophysics, was inaugurated

in 1956 to provide a proper communication for the results of research conducted at the Astrophysical Observatory of the Smithsonian Institution.

Its purpose is the "increase and diffusion of knowledge" in the field of astrophysics, with particular emphasis on problems of the sun, the earth, and

the solar system. Its pages are open to a limited number of papers by other

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Another series is Annals of the Astrophysical Observatory. It was started

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published about every 10 years since that date. These quarto volumes, some

of which are still available, record the history of the Observatory's researches

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Many technical papers and volumes emanating from the Astrophysical

Observatory have appeared in the Smithsonian Miscellaneous Collections.

Among these are Smithsonian Physical Tables, Smithsonian Meteorological

Tables, and World Weather Records.

Additional information concerning these publications may be secured

from the Editorial and Publications Division, Smithsonian Institution.

Washington, D.C.

FEED L. WHIPPLE, Director,

Astrophysical Observatory,

Smithsonian Institution.

Cambridge, Mass.
Meteor Trains1

By ROBERT F. HUGHES

 2

The interaction of meteoroids with the

earth's atmosphere produces in some instances

a luminescence called a meteor train along a

portion of the meteor's visible trail. This light

may last from seconds to hours, and is much less

intense than the luminosity localized about the

ablating meteoroid, which is generally the only

interaction phenomenon observed. Molecular

and atmospheric air motions cause perceptible

expansion, distortion, and displacement of the

meteor train. Photographic observations of

such diffuse and faint sources have been successful only within the last 10 years, and we have

not yet obtained a good spectrogram of a meteor

train which is imperative for understanding the

mechanism responsible for this luminescence.

Visual observations by Trowbridge (1907) of

exceptionally long-enduring trains produced by

bright meteors indicated that meteor trains

form at altitudes from 72 to 104 km, a localized

part of the region from 64 to 130 km where

meteor trails are observed. The longest-enduring trains were even more sharply localized and

occurred at altitudes from 80 to 96 km. The

most probable height of train appearance was

found to be 88 km, with the frequency falling

off rapidly at lower altitudes. The trains observed by Trowbridge had an average duration

of about 15 minutes and they frequently underwent large displacements and distortions, attributed correctly to atmospheric air motions in

the meteor region. The visual data of Olivier

(1947, 1957) indicate the complexity of the

winds in the meteor height region. The study

of these atmospheric winds has also been a part

1

 This paper reports work supported by the Geophysics Research Directorate, Air Force Cambridge Research Center

tinder Contract No. AF 19(122)-482, and by the Army, Navy

and Air Force jointly under Contract AF 19(122)-458, Subcontract 57, with the Lincoln Laboratory of M.I.T. Part of

the reductions were carried out under Contract Nonr1866(05).

2

 Now with General Electric Company, Philadelphia, Pa.

of the meteor train program at the Harvard

College Observatory. This paper presents data

on the heights, trajectories, and orbits of 48

train-producing meteors and on the heights,

durations, and intensity distributions of the

trains.

Instrumentation and reduction methods

Visual observations have indicated that the

distribution of spectral intensity in trains is

different from that in meteors, which are normally blue. Trowbridge (1907) found that

trains appear as yellow or green with a few

strong lines suggestive of the sodium D lines

and the 5182A line of Mgl. Whipple's (1954)

visual observations with a transmission grating

indicated a strong continuum in the yellow and

red regions with a single reddish line. For

photographing meteor trains, therefore, the

ordinary blue-sensitive films were replaced by

Eastman Super-Panchro-Press and a DuPont

Company Panchromatic Film No. 428. The

Super-Schmidt meteor cameras (Liller and

Whipple, 1954) used to obtain photographic

data on meteors and meteor trains were operated from the New Mexico station, whose geographic positions are listed in table 1.

Data on eight of the meteors and their associated trains were reduced by an exact method

developed by Whipple and Jacchia (1957) and

Cook and Hughes (1957). A rapid graphical

method of meteor trail reduction developed by

McCrosky (1957) was used to obtain trajectories and heights for the remaining 40 trains.

This method allowed a complete trajectory

analysis in about 30 minutes with mean errors

in velocity and height around 5 percent.

The absolute visual magnitude at maximum

luminosity was measured by the photometric

process described in detail by Whipple and

Jacchia (1957). A constant meteor color index

79
80 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

TABLE 1.—Positions of meteor cameras

VOL. S

Position

Longitude west

Latitude north

Height above sea level (ft.)

Camera stations

(1952-1954)

Las Cruces

106°36'42. 3 "

32° 18'13. 6"

5,141

Dofia Ana

106°47'58. 4"

32°30'21. 7"

4,632

(1954-1958)

Mayhill

105°28'17. 5"

32°54'44 3 "

6,570

Sac Peak

105°49'13"

32°47'16"

9,253

of —1.9 was assumed. The zenithal correction

to the magnitude was neglected because the

trains were near the zenith, and the average

correction would have amounted to only 0.04

magnitude. Errors due to variations in film

sensitivity, development, and light transmission

are estimated by Jacchia to be about ±0.3 mag.

With a single exception, magnitude measurements made from the two stations agreed within

these limits. Except for possible errors in the

color index, individual absolute visual magnitudes are considered to be accurate within ±0.4

mag.

Orbital elements of train meteors were computed to investigate the type of meteoroids that

produced trains; however, observational errors

preclude the computation of precise individual

orbits, especially for high velocity meteors.

The method of orbital computations detailed

by Porter (1952) was programmed on an electronic computing machine for the 40 trajectories obtained by the rapid graphical method of

reduction. Deceleration due to atmospheric

resistance was neglected. Corrections in velocity and radiant to allow for the earth's attraction are significant only for low velocities and

radiants of large zenith angle, when the true

and apparent values of velocity and zenith

can differ by about 4 km/sec and 5° respectively.

Although the zenithal corrections are comparable to the trajectory errors, they were included in the orbital calculations. The angular

orbital elements, such as inclination, are probably more accurate than the linear elements

involving the semimajor axis.

The heights of meteor trains were determined

by simply matching the fields of the train and

meteor films and noting the dash numbers.

This process was possible because train and

meteor cameras were at the same location. The

maximum and minimum heights, which were

measured on all train films, usually occurred in

the first exposure. The light intensity of most

trains followed a distribution pattern similar to

that of meteors. The intensity increased from

the beginning height to a maximum beyond the

midpoint of the train, then decreased more

rapidly to the endpoint. The heights of maximum intensity were measured.

For 12 of the trains the luminosity was interrupted by a relatively faint region generally

about five meteor dashes in length, which corresponded to 5 to 10 millimeters on the film.

These trains showed effectively two intensity

maxima, although no such variation appeared

in the meteor trails. The double maxima could

be observed even in the first train image, which

corresponds to a train-life of about one or two

seconds. Because this time is so short, these

variations in brightness are considered to be

intrinsic phenomena and not the result of the

influence of air motions on the train.

If the multiple variations were caused by

atmospheric winds, one might expect that

points of minimum train intensity would correspond to heights of maximum wind speeds,

and that points of maximum intensity would

coincide with levels of zero wind. If the correlation coefficient of the horizontal wind field

becomes zero in the vertical direction in a height

interval of about 5 km (Liller and Whipple,

1954), then trails that extend over 25 vertical

kilometers should show as many as five intensity maxima. This argument is based on the

assumption of a sinusoidal variation of the

horizontal wind with altitude. Furthermore, if
NO. 8 METEOR TRAINS 81

the variations were caused by atmospheric

winds, the distance between intensity maxima

should be greater than 10 km. The fact that

the average separation of intensity maxima is

only 7 km and that triple maxima are not observed suggests that the double maximum in

train luminosity is an intrinsic phenomenon.

By the third or fourth image, corresponding to

a train life of about five seconds, one of the

maxima had generally disappeared. During

the remaining lifetime of the train, the intensity distribution resembled that of a single

maximum train. The luminosity in the region

of this second maximum usually remained the

most intense region until the train image disappeared entirely. Three trains were observed,

however, whose last visible portion did not coincide with either maximum.

No trains exhibiting three or more variations

in luminosity were found. For the 12 trains

that showed two maxima, the heights and relative brightness of the maxima in the first or

second images were recorded. For the three

meteor trains in which a "burst" occurred, the

burst region never became the longest enduring

portion of the train.

Without consideration of meteor velocity, the

entire sample of 48 trains was somewhat arbitrarily divided into two groups, those lasting

less than and those lasting longer than about 6.5

seconds. For the 13 trains of longer duration,

the height at which the last luminescence disappeared was called the "persistent" point. No

quantitative measurements were made of the

actual brightness of the train images nor of

their rate of decay.

To estimate the duration of the train we must

consider the operational procedure in detail.

Cook and Hughes (1957) determined that a

time interval ranging from 0.75 to 1.4 seconds

elapsed between the first appearance of the

meteor and the opening of the train camera by

the visual observer. Most of this delay may be

attributed to the reaction time of the observer.

In this paper the duration t of the train is arbitrarily measured from the time of maximum

meteor luminosity. For the average meteor it

is assumed that the time interval between the

opening of the train camera and the first appearance of the meteor is 1.5 seconds. The time

interval between first appearance and maximum

meteor luminosity is about 0.5 seconds. The exposure lengths were 0.5 seconds for the first

image and 2 seconds for the remaining images,

with a negligible time interval between exposures. The mean values of t for the various

images are then 1.25, 2.5, 4.5, 6.5 .. . seconds.

The errors are estimated to be of the order of

one second.

Meteor train data

The data obtained for the meteor trains are

listed in table 2. The asterisks indicate that

the meteor was reduced in detail by Jacchia.

All heights were measured above sea level. The

quantities given in the table are defined as

follows:

Meteor number: The number of the meteor trail as

listed in the Harvard Catalogue.

Date: Time of observation in Universal Time.

Class: Name of the shower to which meteor belongs.

A blank indicates a sporadic meteor.

Corr. rad.: Apparent radiant corrected for zenith attraction (Equinox 1950).

V: Meteor's velocity in the atmosphere (km/sec).

Va: Heliocentric velocity of meteor at time of capture

(km/sec).

a: Seinimajor axis of the orbit (a.u.).

e: Eccentricity of the orbit

q: Perihelion distance (a.u.).

q': Aphelion distance. "Hyperbolic" orbits are indicated by oo (a.u.).

«; Argument of perihelion measured along the orbit

from the node in the direction of motion (Equinox

1950).

A : Longitude of the ascending node (Equinox 1950).

i: Inclination of the orbital plane to the ecliptic

(Equinox 1950).

e: Apparent elongation angle, the angle between the

earth's apex and the apparent radiant of the

meteor.

cos z: Cosine of the zenith angle.

M,t.: Absolute visual magnitude of the meteor at maximum luminosity.

Duration: Duration of train (sec.).

H>.,(M): Height (km) of the beginning point of

meteor.

Hm-(M): Height (km) of maximum meteor luminosity.

H^tiM): Height (km) of the end point of meteor

trail.

J5r».f(D: Height (km) of the beginning point of the

train.

H^(T): Height (km) of the end point of the train.

Hx: Height (km) of the brightest point of the train

in the first exposure.
82

SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS VOL. 3

H%: Height (km) of the fainter maximum in the first

to third exposures, in trains showing two intensity

maxima.

H,: Height (km) of persistent point of train.

Train-producing meteors: Magnitude distribution

Among the 48 photographic train meteors described in table 2, only seven were members of

meteor showers. The Perseids and Southern

Taurids each produced three train meteors, and

the Geminids one. The successfully recorded

trains produced by sporadic meteors occurred

in equal numbers in the periods January to June

and July to December. In the latter period the

observed trains were concentrated in the winter

months of November and December, which is to

be expected from the weather conditions in New

Mexico. A histogram showing the distribution

of magnitudes of train-producing meteors is

shown in figure 1.

The faintest meteor that can be photographed

with the Super-Schmidt meteor cameras has an

absolute visual magnitude about +4. The

faintest train-producing meteor detected had a

magnitude of +2.5. The difference between

these magnitudes is due to the fact that train

meteors have a high velocity. The number of

train-producing meteors increases with increasing meteor magnitude until we approach the

limits of sensitivity. We may infer that formation of meteor trains in the earth's atmosphere

is a common phenomenon, although the occurrence of luminescence lasting ten minutes or

more is obviously very rare.

Train-producing meteors: Velocity

The velocities of 48 train meteors are shown by

a histogram in figure 2. About 12 percent of the

meteors have velocities between 70 km/sec and

the parabolic limit, and more than 80 percent

have velocities greater than 50 km/sec. No

train meteors were observed with velocities less

than 20 km/sec. The mode lies between 60 and

70 km/sec and the average is about 60 km/sec.

The predominance of high velocities is indicated

by comparing figure 2 with a similar histogram

in figure 3 (Hawkins and Southworth, 1958).

Although 80 percent of the meteors in figure 3

have velocities less than 50 km/sec, only a small

percentage of such meteors produce trains.

£ 10

+ 5 +4 +3 +2 +1 0 -1 - 2 - 3 - 4 -5

Absolute Visual Magnitude

FIGURE 1.—Percentage distribution according to magnitude of

48 train-producing meteors.

60r

50

40

30

20

10

20 30 40 50 60

Atmospheric Velocity (km/sec)

70 72.1

FIGURE 2.—Percentage distribution according to velocity of

48 train-producing meteors.
NO. 8 METEOR TRAINS 83

10 15 20 25 30 35 40 45 50 55 60 65 70 75

FIGURE 3.—Velocity distribution of 252 sporadic and 49

shower meteors.

120 r

110 -

Train heights

Figure 4 shows a plot of the data given in table

2 for the heights of the beginning point, end

point, maximum intensity, and persistent points

of each train. Figure 4 also shows the mean

beginning height and end height of the meteors

that produce the trains. A correspondence

exists between the beginning heights and end

heights of meteor and train, except that at low

velocities the beginning height of the train is

below that of the meteor. For the trains of very

long duration, however, Trowbridge (1907) and

Olivier (1957) observed no relationship between

the extreme points of the meteor trail and train.

This indicates the restricted height region of

train formation. The meteors producing these

trains of very long duration were generally ex100

90

80

70

60

50

40

beginning

end

e Beginning Height

• Maximum Intensity in First Image

- Fainter Maximum

a Persistent Point

• Meteor Burst

x End Height

—•Mean Heights of Train Meteors

10 20 30 40 50 60

Atmospheric Velocity (km/sec)

FIGURE 4.—Heights of 48 trains and train-producing meteors.

70
84 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS VOL. 3

tremely bright fireballs. They would therefore

have trail extremity points outside of the 70-120

km region and no correlation would be expected.

The relatively fainter and more numerous meteors observed with the Super-Schmidt cameras

have trails that are within the height region of

70-120 km in which the trains are found.

The correlation between the heights of meteor

trails and trains is readily seen in figures 5 and

6. For most individual meteors, the trail extremities defined the limits of train formation,

although a few trains did fall outside this

range. With meteors of lower velocities, the

trains with midpoints at heights around 85 km

120

tend to be shorter than the trails. We may

write the relation between the beginning heights

of trains, Hbeg(T), and of meteor, JSbeg(M), as

Hbee(T)=lA7 Hbeg(M)-57 (km) (1)

and the relation between the end heights as

Hend(T)=Hen*(M)+2 (km). (2)

The standard deviation for equation (1) is

about ±3 km, and for equation (2) it is ±1.5

km. Thus the correlation is slightly better for

the end heights than for the beginning heights.

The close relationship between the endpoints

of trains and meteors suggested a similar relation between maximum luminosity in trains and

110

00

100

90

80

90 100 no 120

Begfnning Height of Meteor Trail (km)

FIGURE 5.—Correlation between beginning heights of meteor trains and trails.
NO. 8 METEOR TRAINS 85

80 90

End Height of Meteor Trail (km)

100

FIGURE 6.—Correlation between end heights of meteor trains and trails.

in meteors. The relevant data are plotted in

figure 7 for 36 trains that showed only a single

intensity maximum along the trail. Included

among this number are five persistent trains.

The graph clearly indicates a coincidence of

the heights of maximum intensity for trains and

meteors. The agreement appeared to be independent of the exact number of the images, i.e.,

whether the duration of the train was short or

long. This statement must be qualified somewhat, however, because one of the five trains

lasting longer than 6.5 seconds departed significantly from this relationship. This train

meteor was a member of the Southern Taurid

shower, with Hmaa!(M)=78 km and H^T)

=87 km. This apparent exception, however, is

actually typical of long duration trains formed

by low velocity meteors (see p. 87).

Figure 8 shows a plot of the heights of 12

trains that exhibited double maxima against the

height of maximum meteor luminosity; 8 of the

12 trains had durations greater than 6.5 seconds,

while only 5 out of 34 trains showing a single

maximum had such durations. The average

duration of the double maxima trains was

longer than that of the single maximum trains.

502074—69 2

Figure 8 indicates that the lower maximum coincides with Hmam(M) for altitudes above about

85 km. The lower maximum was brighter than

the upper in the first and second exposures for

75 percent of the trains.

Train durations

Duration of meteor trains varies with meteor

magnitude and velocity, as shown in figures 9

and 10. The solid curves in figure 9 represent

visual data taken from Millman (1950). Although the scatter is quite large, the curves suggest that the duration of trains increases with

meteor magnitude for durations less than 12

seconds. The increase amounts to about 5 seconds per magnitude. The trains formed by low

velocity meteors, as a group, deviate the most

from Millman's curves. These meteors produce the trains in the constant-height region 85

to 95 km, far above the height of maximum

meteor luminosity as shown in figure 8.

Figure 11 shows a plot of meteor magnitude

against meteor velocity for the two groups of

trains having durations less than and greater

than 6.5 seconds. The magnitude-velocity variation for the latter group is normal, since
86 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS VOL. 3

110

£100

90

80.

70

• Train Duration < 6.5 sec.

B Train Duration > 6.5 sec.

80 90 100 110 120

Height of Maximum Meteor Luminosity (km)

FIGURE 7.—Correlation between heights of maximum luminosity of meteors and trains with single maximum.

110

iioo

•I

90

80

70 80

* Maximum Intensity in First Image

*• Second and Fainter Maximum

O Persistent Point

90 100

Height of Maximum Meteor Luminosity (Km)

110 120

'•. •

FIGURE 8.—Correlation between heights of maximum luminosity of meteors and trains with two maxima.
NO. 8 METEOR TRAINS 87

71 km/sec

20

18

16

14

12

10

8

6

4

2

+4 +3 +2 +1 0 - 1 - 2 -3 - 4

Meteor Absolute Visual. Magnitude

FIGURE 9.—Variation of train duration with magnitude of

meteor.

luminous intensity increases with increased

mass and velocity of the meteoroid. A difference of about four magnitudes exists between

the meteors of low and high velocity, a value

consistent with the assumption that the meteoroids in each group have equal masses and

zenith angles.

Thus the probability of observing a longduration train depends to some extent on the

energy of the meteor. It must be remembered

however that the probability of observing a

train may also depend on atmospheric and other

conditions that can affect its rate of decay.

The heights of the persistent point for 13

trains with durations greater than 6 seconds are

plotted in figure 12. These heights range from

87 to 107 km with an average value of 94 km

and a dispersion of 6 km. The relation of the

persistent height to Hmax(M) was seen in the

previous sections to be similar to that of the

single and double maxima; that is, the persistent points coincide with the heights of maximum meteor luminosity except in the region

where Hmax(M) is less than 85 km. All of the

five persistent points at heights above 96 km

were formed by high-velocity meteors. The

obvious lack of persistent trains in the region

below 85 km qualitatively agrees with the values

of Liller and Whipple (1954) for the large

decay rate of luminescence in this region. A

striking example of this phenomenon is the

meteor of June 29,1954, which burst at 83 km;

yet the height of the persistent point was 92 km.

On the other hand, another meteor which burst

at 91 km showed a persistent point at 97 km.

Orbits of train meteors

The three train-producing meteors of low

velocity, with persistent points much greater

than Hmax^M), were shower meteors, one

Geminid and two Southern Taurids. Their

orbits are characterized by small inclinations,

perihelion distances less than 0.4 a.u., and

aphelion distances that lie within Jupiter's

orbit. The remaining five low-velocity trainmefeors listed in table 2 had heights of maxi20

18

16

14

12

10

0 10 20 30 40 50 60 70

Atmospheric Meteor Velocity (km/sec)

FIGURE 10.—Variation of train duration with velocity of

meteor.
88 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS VOL. 3

D

. • *

• Train Duration < 6.5 sec.

O Train Dunrtk>n>6.5 sec.

10 20 30 40 50 60 70

Atmospheric Meteor Velocity (km/ sec)

FIGURE 11.—Variation of magnitude with velocity for train

meteors.

mum luminosity greater than 85 km which coincided with the height of maximum train

luminosity. Two of these train meteors were in

orbits identical to those of the three shower

meteors; the others had small inclination angles

but the perihelion distances were about unity

and aphelion distance lay beyond Jupiter's

orbit

In summary, five out of eight low-velocity

train meteors possessed orbits of short period,

low inclination, and high eccentricity; the other

three were similar except that they had longer

periods. The average value of the eccentricity

of the low-velocity meteors was 0.87. Individual values were all greater than 0.8, which made

the value of the cometary-asteroid criterion, K

(Whipple 1954), greater than zero for each

orbit.

The trains with the five largest Hmax(M)

were formed by high-velocity meteors, one of

which was a Perseid. Each of these five train

meteors possessed an orbital inclination greater

than 120°, aphelion distance greater than 6 a.u.,

and four of them had perihelion distances near

unity. Eccentricities were about unity with one

exception, when e=0.7, a value that is still

.100

90

80

° Persistent Point

• Burst Point

70 80 90 100

Height of Maximum Meteor Luminosity, (km)

110 120

FIGURE 12.—Heights of persistent point of meteor trains.
NO. 8 METEOR TRAINS 89

larger than the asteroidal limit. The cometasteroid criterion was positive for these meteors

also. The meteors that provided the two longest-duration trains were among this group.

The five longer-duration trains with Hmam(M)

near 85 km resulted from both high and low

velocity meteors.

The trains of short duration were formed by

high velocity meteors. With the single exception of the meteor of April 27,1954, the inclination angles are greater than 90°, aphelion

distances are greater than 8 a.u., and the eccentricities are larger than 0.8; these values make

the cometary-asteroid constant strongly positive. Orbits with eccentricity values near unity

resulted in perihelion distances less than 0.5 a.u.

for 25 percent of the 31 train meteors of short

duration. The majority had a perihelion distance, g=l a.u., a value consistent with their

greater probability of observation.

Figure 13 shows regions of positive and negative values of the cometary-asteroid criterion

(K) inequation (3).

(3)

Of the 48 meteors, only the one of 3 January

1954 appeared in the asteroidal region of negative K, but this meteor had a high atmospheric

velocity, an apparent elongation angle of only

17°, and an orbital inclination of 150°. Since

retrograde orbits are not characteristic of

asteroidal orbits, this meteor is also a cometary

meteoroid.

.a

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.3 .4 .5 .6 .7 .8

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FIGURE 13.—Distribution of aphelion and perihelion distance!.

1.0
90 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS VOL. S

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94 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS VOL. 3

Summary

The analysis of 48 meteor trains photographed

with Super-Schmidt cameras indicates the following characteristics of trains: (1) Train formation occurs throughout the meteor region

from 70 to 120 km. (2) The frequency of trains

is much greater than previously suspected. ( 3)

Train formation is much more efficient at higher

meteor velocities. (4) Train meteors exhibit

the usual relation between height and velocity.

(5) For train meteors with a maximum higher

than 85 km, the point of maximum light and

the persistent point of the train coincide. The

same correlation was shown, at heights above

85 km, by the lower maximum of a doublemaximum train. (6) Persistent luminescence

lasting about 10 seconds occurs between heights

of 110 km and 85 km. The average height is

94 km. (7) The duration of a train depends

both on the degree of initial atomic activation

by the meteor and on environmental conditions.

(8) 75 percent of the train meteors move in

retrograde long-period orbits, and the remaining meteors move in direct short-period but

highly eccentric orbits.

References

COOK, A. F., AND HUGHES, R. F.

1957. Smithsonian Contr. Astrophys., vol. 1, pp.

225-237.

HAWKINS, G. S., AND SOUTHWOBTH, R. B.

1958. Smithsonian Contr. Astrophys., vol. 2, pp.

349-364.

LlIXEB, W., AND WHIPPLE, F. L.

1954. In Boyd and Seaton, eds. Rocket exploration of the upper atmosphere, p. 112.

MCCBOSKT, R. E.

1957. Smithsonian Contr. Astrophys., vol. 1, pp.

215-224.

MIIXMAN, P. M.

1950. Journ. Roy. Astron. Soc. Canada, vol. 44,

pp. 209-220.

OLIVIER, C. P.

1947. Journ. Amer. Phil. Soc., vol. 91, pp. 315-327.

1957. Journ. Amer. Phil. Soc., vol. 101, pp. 296-

315.

POSTER, J. 6 .

1952. Comets and meteor streams. 160 pp., 26

figs.

TBOWBBIDGE, C. O.

1907. Astrophys. Journ., vol. 26, pp. 95-116.

WHIPPLE, F. L.

1954. Astron. Journ., vol. 59, pp. 201-217.

WHIPPLE, F. L., AND JACCHIA, L. G.

1957. Smithsonian Contr. Astrophys., vol. 1, pp.

183-206.

Abstract

Data are presented on the heights, durations, and intensities of 48 meteor trains. The beginning and end points

of the meteor trains correlated well with those of the meteor trail. The points of maximum train intensity coincide

with the heights of maximum meteor luminosity throughout the life-time of the luminescence, for trail maxima above

85 km. The atmospheric region below this altitude is very unfavorable for the occurrence of long duration trains.

The initial formation of a train is much more efficient for high velocity meteors. The relatively longer duration

trains show no velocity preference due to a balance between the higher probability of train formation by high velocity, hence high altitude meteors, and the greater probability of persistence for a train formed at lower altitudes, by

low velocity meteors. About three-fourths of the train meteors move in retrograde long-period orbits and the remaining train meteors with low atmospheric velocities move in direct, short-period, and highly eccentric orbits. The

cometary-aateroid criterion suggested by Whipple indicates that all the trains were formed by cometary meteoroids.