Leonid Meteor Research Articles

Video Observations Of Leonids 1999

We analyse data obtained by different ground-based video camera systems during the 1999 Leonid meteor storm. We observe similar activity profiles at nearby observing sites, but significant differences over distances in the order of 4,000 km. The main peak occured at 02:03 UT (λ⊙=235.286, J2000, corrected for the time of the topocentric stream encounter). At the Iberian peninsula quasi-periodic activity fluctuations with a period of about 7 min were recorded. The camera in Jordan detected a broad plateau of activity at 01:39–01:53 UT, but no periodic variations. The Leonid brightness distribution derived from all cameras shows a lack of faint meteors with a turning point close to +3m, which corresponds to meteoroids of approximately 10-3 g. We find a pin-point radiant at αalpha=153.65 ±0.1, δ=21.80 ±0. (λ⊙=235.290). The radiant positionis identical before and after the storm, and also during the storm no driftis observed.

Observations of the 1996 Leonid meteor shower by radar, visual and video techniques

The activity of the 1996 Leonid shower from two radars, global visual and single-station low-light-level TV (LLTV) observations is presented and summarized. Radar observations from Ondřejov in the Czech Republic indicate a peak rate of (>+1) Leonids near λ⊙ = 235°2±0.1 (Equinox 2000). As observed by this radar, this peak interval was characterized by a significant increase in the number of bright Leonids as demonstrated by a noticeable lowering of the mass index near the peak. From radar observations in Ontario, Canada (using the CLOVAR system), a raw peak flux of 1.3±0.3×10−2 meteoroid km−2 h−1 brighter than radio magnitude +7.7 was reached at λ⊙ = 235°3±0.1, uncorrected for initial train radius effects. Single-station LLTV observations suggest a peak shower flux of 1.8±0.4×10−2 meteoroid km−2 h−1 brighter than absolute magnitude +5±0.5 between 235°3 and 235°39. The position of the radiant on the night of maximum of the shower is found to be α=152°9±1°0 and δ=22°1±1°0 from CLOVAR observations and α=153°3±1°7 and δ=22°1±1°7 from LLTV observations. Visual observations of the shower yield a peak zenithal hourly rate (ZHR) of 86±22 at 235°17±0°07 or an equivalent flux of 1.2±0.4×10−2 meteoroid km−2 h−1 brighter than absolute visual magnitude +6.5. The visual peak was short-lived (1.5 ± 0.5 h HWHM) and richer in fainter meteors than neighbouring intervals. Discrepancies in the estimated absolute Leonid flux found using differing methods are noted and possible reasons for the differences discussed. The stream in 1996 showed two distinct meteoroid populations: a population of recently ejected meteoroids rich in smaller particles near 235°17 which is very narrow in nodal extent (HWHM 0°07±0°02), and an older component (of order 10 revolutions in age) peaking near 235°4 which is rich in larger stream meteoroids, of long duration (FWHM 1°2 ±0°4), which contributed most to the total mass flux at Earth from the stream in 1996.

The Leonid meteors: compositions and consequences

The Leonid meteors: compositions and consequences

Things that go bump in the night sky

The Leonid meteor shower, caused by debris from the comet Tempel-Tuttle, is sometimes spectacular. The Leonids of 1833 even made audible hissing, crackling and popping sounds, probably ‘electrophonic sounds’, produced by radio waves generated in the meteoroids' wakes. But this implies that some of the meteoroids must have been over a metre across — too big to escape the comet in the usual way, by sublimation pressure.

Possible detection of meteor stream effects on the lunar sodium atmosphere

We report two sets of observations of sodium emission from the lunar atmosphere. The spectra were taken on two nights having very similar lunar phases, at various distances from the limb. Using Chamberlains model of the exosphere, we obtained values of the temperature, scale height and number density at the surface. These values differ significantly between the two nights. The spectra of the first night were taken when the Earth–Moon system was entering the Leonid meteor stream and show a marked increase in intensity, temperature and scale height relative to those of the second night, and relative to data for similar lunar phases published in the literature. We believe that this increase is related to an enhanced flux of micrometeoroids associated with the Leonid and possible with the Taurid meteor streams. The micrometeoroid component is generally considered the least important contribution to the sodium flux, and its distribution is assumed to be isotropic. We have previously suggested that an anisotropic and enhanced micrometeor component could be associated with meteor streams. The results reported below support this suggestion.

Meteor luminosity at 160 km altitude from TV observations for bright Leonid meteors

Two atmospheric trajectories have been determined by simultaneous observations with image intensifier‐fitted TV cameras and conventional photographic cameras for two bright Leonid meteors (fireballs) in 1995 and 1996. Beginning heights recorded by the photographic method are lower than about 130 km, but those observed by the TV systems are closer to 160 km. The primary reason for this difference is the sensitivity of the observing systems. However, the difference in the sensitive wavelengths (up to 900 nm for the TV systems) could be another factor contributing to the large difference between the two methods. This suggests that the beginning heights of high speed bright meteors such as Leonid meteors are much higher than previously thought.

The Leonid meteor showers and the genesis of the Ancient Mariner

The Leonid meteor showers and the genesis of the Ancient Mariner

Computation of atmospheric entry flow about a Leonid meteoroid

The flow field is computed around a 1 cm diameter Leonid meteoroid as it enters the Earth's atmosphere at an altitude of 95 km and a velocity of 72 km/s. These conditions correspond to a Knudsen number of 4 and a Mach number of 270. To accurately compute the gas flow, these extreme nonequilibrium conditions require application of a kinetic approach and the present work employs the direct simulation Monte Carlo method. A meteoroid ablation model is included in the computations and is found to play a significant role. The computational results predict that a large region of the flow field is affected by meteoroid ablation that produces an extended wake at high temperature in a sate of thermal equilibrium. These findings are in qualitative agreement with spectroscopic observations of the 1998 Leonid meteoroid shower. The computations indicate that the results are sensitive to the material properties assumed for the meteoroid.

Comet Tempel-Tuttle and the Leonid Meteors

The annual November Leonid meteor showers and the occasional Leonid meteor storms (e.g. 1833, 1966) are far better known than is the Leonid parent body, comet 55P/Tempel-Tuttle. Since A.D. 902, enhanced Leonid meteor showers have been recorded around the time of the parent comet’s returns to perihelion (Yeomans 1981). To date, the parent comet itself, however, has not been seen for more than a few days at any apparition except in late 1865 and early 1866. The impending perihelion return of comet Tempel-Tuttle again raises the possibility of strong meteor displays in 1998-99 as well as a chance to observe the elusive parent comet.

Observations of the Leonids over the Last Millenium

The recognition of the astronomical origin of meteors is intimately connected to the Leonid meteors, and their tendency to “storm” with a period of 33 years. It was the Leonid storm of 1799, observed by Alexander von Humboldt among others, that first established the geographical extent of the phenomenon, with observations reported over 90 degrees of longitude and 60 degrees of latitude. During the 1833 storm, Olmsted (1834) at Yale and Twining (1834) at West Point established the radiant point in Leo, and the cosmic origin was clinched when H. A. Newton (1863), also at Yale, determined that the cycle repeated in intervals of sidereal years, not tropical years. Inspired by the 1866 storm, Adams (1866), Schiaparelli (1867), and Le Verrier (1867) determined a 33.25 year period and other orbital elements for the meteor stream; two years after the discovery of Comet Tempel-Tuttle in 1865, that comet was recognized as the parent body of the Leonid stream after von Oppolzer (1867) calculated a period of 33.17 years for the comet. Astronomers confidently predicted another storm in 1899, but none appeared, though there were good showers in 1901-1903. The years 1930-32 also brought fairly good showers, but 1966 brought the strongest storm witnessed in modern times, with an estimated 100,000 meteors per hour. Steady progress was made in meteor studies in the 20th century, especially with new photographic and radar techniques. The current question is what will happen in the 1997-1999 period; the only certainty is that the event will be studied with an even wider array of techniques.

RADAR Observations of Leonids in Japan

We are observing meteor showers using the MU radar located at Shigaraki, Japan. This is a Mesosphere, Stratosphere and Troposphere radar, belonging to the Kyoto University, with a frequency and a peak power of 46.5M.ffz and 1MW, respectively. This system is characterized by the versatility of the antenna array. By using four antennas out of 475 Yagi arrays together with four receiver channels, we can observe more than several hundred meteor echoes per hour. The beam applied at the meteor observation is a static “doughnut beam”, which is the rotational symmetrical pattern to the vertical line. This beam is effective enough to detect meteor echoes of which the zenith angle is smaller than about 50°, which characterizes the MU radar as an all sky monitoring radar of meteor echoes. For the low velocity meteors, most of the echoes satisfy a condition of the perpendicular reflection, and we can derive the position of the radiant point statistically, and succeeded its application for the Geminids (Watanabe et al. 1992a). For the high velocity meteors, most of the echoes are in the overdense condition. However, we can discriminate the echoes of a specific meteor shower out of the data by checking the echo duration, the height, the strength or the combination of them. We have been monitoring the Perseids from 1990, and succeeded to reveal the unusual activity in 1991 (Watanabe et al. 1992b). For the Leonids, we are continuing the observation from 1991. The drastic increase of the activity has been detected around 23h UT on November 17, 1994. The number of the observed long duration echoes, which came from possibly bright Leonids meteors, were 80 per hour. This should be the beginning of the Leonids activity toward the 1998-1999. We are planning to continue this observation until the end of the activity in the 2000’s.

Visual observations of the Leonid meteors 1998 in Yunnan

The 1998 Leonid meteor shower was observed at the Gaomeigu station of Yunnan Observatory during five successive days in November. The visual records indicate that the number of meteors increased suddenly, from a ZHR of about 140 to over 400, in the early morning of November 17th, Beijing time. But it decreased slowly in the following two days. During the maximum there was a high proportion - about 10 percent - of very bright fireballs with enduring trains. The brightest one was about -10 magnitude with a smoke train fading about three minutes after.

An Airborne Stereoscopic Mission to Explore the 1998 and 1999 Leonid Meteor Storms

The possibility of a storm of Leonid meteors in November 1998 and 1999 offers exciting opportunities for using unusual meteor observing techniques, because of high flux and because the Leonids are unique probes for the study of the parent comet 55P/Tempel-Tuttle and the Earth’s upper atmosphere.

Observations of the Leonids in Central Asia

Observations in Central Asia in 1965-1966 by both photographic and radar methods allowed a determination of the radiants and orbits of Leonids (Babadzhanov and Getman 1970). Photographs showed that meteoroids undergo quasi-continuous fragmentation (QCF) in the Earth’s atmosphere. Taking account of QCF, the density of the Leonid meteoroids were found to lie between 1 and Agcm-3 the average being 2gcm-3 (Babadzhanov 1994), in agreement with the density range of between 0.2 and 6gcm-3 given by Maas et al (1990) for dust grains from comet P/1 Halley, with values below 0.6 being rare. Further, the icy grains have a density of about 1gcm-3 while silicate grains have a mean density 2.5 times higher.

The Leonid meteor shower: why are there storms but no regular annual activity?

The Leonid meteor shower: why are there storms but no regular annual activity?

Meteor shower radiant positions and structures as determined from single station video observations

Single station video observations of meteors can be used for the precise determination of radiant positions of major and minor meteor showers. Video systems combine large quantities of recorded events with high accuracies, and are therefore applied in the investigation of fine structures within the radiant. In the past four years, amateurs from the Archenhold-Observatory Berlin have been operating the wide angle video system MOVIE. The maxima of several major meteor showers could be recorded. The video tapes were digitized and analysed on PCs. Using the Radiant software developed within the International Meteor Organization, the position was determined of the Quadrantid (α = 229.4° ± 1.5°, δ = +49.7° ± 1.5°), Lyrid (α = 271.6° ± 1.5°, δ = +32.9° ± 1°), Perseid (α = 46.0° ± 2°, δ = +57.7° ± 2°), Orionid (α = 93.6° ± 1°, δ = +14.9° ± 1°) and Leonid (α = 154.5° ± 2°, δ = +21.4° ± 1°) meteor shower radiants and possible radiant fine structures searched for. The obtained radiant positions are in good agreement with the common values in the literature; no significant fine structures could be found. From the video records of the 1995 α-Monocerotid outburst, a radiant at α = 117° ± 3° and δ = +1° ± 2° was derived, which proves older results to be in error by several degrees.

Precisely reduced meteoroid trajectories and orbits from the 1995 Leonid meteor outburst

The discovery of enhanced Leonid activity in 1994 led to the mounting of a multi-station photographic campaign on two continents during the Leonids of 1995. The goal was to determine orbits and trajectories of outburst Leonids. The outburst did recur as predicted, resulting in 23 precisely reduced Leonid orbits and 30 Leonid trajectories. Individual velocities and radiant positions, as well as the average orbit are presented. It is found that the distribution of Leonid radiants contains a dense cluster of seven radiant positions. This clustering is tentatively associated with the visually observed outburst component. These seven meteors provide the first orbital elements of outburst Leonids and put strong constraints on theoretical models of the origin and evolution of the Leonid stream.

The Impending Appearance of Comet Tempel–Tuttle and the Leonid Meteors

Using the available observations in 1699, 1865–1866, and 1965, an orbit has been recomputed for periodic comet 55P/Tempel–Tuttle, the parent body of the Leonid meteors. The comet's motion was numerically integrated back in time for two millennia and ephemerides were computed for each perihelion return. Chinese observations of the comet in 1366 are well represented, and possible (but not definite) observations of the comet in October 1234 and January 1035 have been identified. The Leonid meteors have been observed sinceAD902. Prior to the eighth century, no Leonid meteors should have been visible because the comet's orbit passed too far outside that of the Earth. By using previously recorded accounts of the Leonid meteor showers and storms as a guide, predictions for the forthcoming Leonid displays in November of 1996–1999 are provided. The 1998 and 1999 events hold the most promise for an impressive Leonid meteor display, although there seems little likelihood that the great storms of 1833 and 1966 will be repeated at this apparition.

Meteor stream activity. III. Measurement of the first in a new series of Leonid outburst

Abstract— In 1994 November, a shower of bright Leonid meteors signaled what is likely the first meteor outburst of Leonids associated with the upcoming return of comet P/Tempel‐Tuttle to perihelion. Measurements of meteor activity and the meteor brightness distribution are presented. By comparing the present observation with those of past Leonid returns, a forecast is made of the time, the duration, the intensity, and the mean meteor brightness of Leonid outbursts that may occur if previously observed patterns are repeated in the forthcoming years.

The Leonid outburst of 1996

There is strong anticipation that the Leonid meteor shower could produce storm-level activity in 1998 and/or 1999. The well-documented Leonid outburst in 1996 and the more poorly observed one in 1994 have been taken by many observers to imply that a storm is imminent, This article explores the possible relationship between the 1996 outburst in activity and possible Leonid storms. The curve of activity is found to be much closer to that of normal activity, although with greater hourly rates, than it is to the very brief, steeply rising activity curve of a storm. It is probable that the 1996 outburst is thus completely unrelated to any future storm which may appear.