Orionid Meteor Showers Research Articles

A Reference Meteor Magnitude for Intercomparable Fluxes

The rate at which meteors pass through Earth’s atmosphere has been measured or estimated many times over; existing flux measurements span at least 12 astronomical magnitudes, or roughly five decades in mass. Unfortunately, the common practice of scaling flux to a universal reference magnitude of +6.5 tends to collapse the magnitude or mass dimension. Furthermore, results from different observation networks can appear discrepant due solely to the use of different assumed population indices, and readers cannot resolve this discrepancy without access to magnitude data. We present an alternate choice of reference magnitude that is representative of the observed meteors and minimizes the dependence of flux on population index. We apply this choice to measurements of recent Orionid meteor shower fluxes to illustrate its usefulness for synthesizing independent flux measurements.

Activity of the Eta-Aquariid and Orionid meteor showers

Aims.We present a multi-instrumental, multidecadal analysis of the activity of the Eta-Aquariid and Orionid meteor showers for the purpose of constraining models of 1P/Halley’s meteoroid streams.Methods.The interannual variability of the showers’ peak activity and period of duration is investigated through the compilation of published visual and radar observations prior to 1985 and more recent measurements reported in the International Meteor Organization (IMO) Visual Meteor DataBase, by the IMO Video Meteor Network and by the Canadian Meteor Orbit Radar (CMOR). These techniques probe the range of meteoroid masses from submilligrams to grams. Theη-Aquariids and Orionids activity duration, shape, maximum zenithal hourly rates values, and the solar longitude of annual peaks since 1985 are analyzed. When available, annual activity profiles recorded by each detection network were measured and are compared.Results.Observations from the three detection methods show generally good agreement in the showers’ shape, activity levels, and annual intensity variations. Both showers display several activity peaks of variable location and strength with time. Theη-Aquariids are usually two to three times stronger than the Orionids, but the two showers display occasional outbursts with peaks two to four times their usual activity level. CMOR observations since 2002 seem to support the existence of an ~12 yr cycle in Orionids activity variations; however, additional and longer term radar and optical observations of the shower are required to confirm such periodicity.

A research of the Orionid meteor shower by television observations in 2006–2008

The results of observations of the Orionid meteor shower are given in the period from 2006 to 2008. Observations were carried out using a highly sensitive camera FAVOR (FAst Variability Optical Registrator) a limiting magnitude of above +11.0m (for stars) and a field of view of 18° × 20°. Over the period of the shower from October 2 to November 7, 2006–2008, there were 3713 meteors. 449 of these meteors were associated with the Orionid meteor shower. The distributions of Orionid meteors by the stellar magnitude is presented. It turned out that most of meteors (65%) of this shower have a brightness of +5.0m-+7.0m. On each night of observation the index of meteor activity was calculated for Orionids.

First results from the 2009-2010 MU radar head echo observation programme for sporadic and shower meteors: the Orionids 2009

The aim of this paper is to demonstrate the capabilities of a new automated analysis scheme developed for meteor head echo observations by the Shigaraki middle and upper atmosphere (MU) radar in Japan (N, E). Our analysis procedure computes meteoroid range, velocity and deceleration as functions of time with unprecedented accuracy and precision. This is crucial for estimations of meteoroid mass and orbital parameters, as well as investigations into meteoroid–atmosphere interaction processes. We collected an extensive set of data (>500 h) between 2009 June and 2010 December. Here, we present initial results from data taken in 2009 October 19–21. More than 600 of about 10 000 head echoes recorded during 33 h were associated with the 1P/Halley dust of the Orionid meteor shower. These meteors constitute a very clear enhancement of meteor radiants centred around right ascension α= and declination δ=. Their estimated atmospheric entry velocity of 66.9 km s−1 is in good agreement with 1P/Halley dust ejected in the year 1266 bc, which, according to simulations, crossed Earth’s orbit at the time of our observation. The Orionid activity within the MU radar beam reached about 50 h−1 during radiant culmination. The flux of sporadic meteors in the MU radar data, coming primarily from the direction of the Earth’s apex, peaked at about 700 h−1 during the same observations.

Modulational excitation of low-frequency dust acoustic waves in the Earth’s lower ionosphere

During the observation of Perseid, Leonid, Gemenid, and Orionid meteor showers, stable low-frequency lines in the frequency range of 20–60 Hz were recorded against the radio-frequency noise background. A physical mechanism for this effect is proposed, and it is established that the effect itself is related to the modulational interaction between electromagnetic and dust acoustic waves. The dynamics of the components of a complex (dusty) ionospheric plasma with dust produced from the evolution of meteoric material is described. The conditions for the existence of dust acoustic waves in the ionosphere are considered, and the waves are shown to dissipate energy mainly in collisions of neutral particles with charged dust grains. The modulational instability of electromagnetic waves in a complex (dusty) ionospheric plasma is analyzed and is found to be driven by the nonlinear Joule heating, the ponderomotive force, and the processes governing dust charging and dynamics. The conditions for the onset of the modulational instability of electromagnetic waves, as well as its growth rate and threshold, are determined for both daytime and nighttime. It is shown that low-frequency perturbations generated in the modulational interaction are related to dust acoustic waves.

The Halley comet meteor stream: numerical modelling of its dynamic evolution

The ribbon-like model proposed by McIntosh & Hajduk for the structure of the Halley meteor stream explained many of the features of the Eta Aquarid and Orionid meteor showers. This model is here verified quantitatively by numerically integrating the orbital motion of up to 500 test particles over several millennia. Perturbations by the major planets, the effect of radiation pressure and Poynting–Robertson drag, are all taken into account. The stream cross-section becomes highly elongated in only a few thousand years. Concentrations in the particle distribution are apparent for larger particles. Meteors now seen in the Orionid shower were injected into the stream earlier than a few thousand years ago whereas in the Eta Aquarid shower we see particles released more recently.

The flux of meteoroids in the vicinity of the orbit of Comet Halley

On the basis of simultaneous observations of the Orionid meteor shower in Italy and Czechoslovakia during the period 1978–1982 the flux densities of meteor particles in the near-perihelion distances have been derived and related to previous results of observations of the shower associated with Comet Halley. A maximum flux rate of 2·10−10 m−2 s−1 has been obtained for the particles of the mass range higher than 10−6 kg at the distances of (0.09÷0.005) A.U. from the orbit of the comet. The flux in the most inner core of the stream, relative to the particles of the mass range lower than 10−6 kg, is controlled by the fresh cometary ejecta and hence depends on the mass-loss rate of the of the comet and on its gas/dust relation. The meteor shower observations yield a mass loss rate of solid particles of 3.3·1011kg/revolution. Ths value increases the hazard of the space experiments by more than 1 order of magnitude.

The luminosity functions of the 1969 Perseid and Orionid meteor showers

Visual counts of the 1969 Perseid and Orionid meteor showers are presented, comprising 288 Perseids and 56 Orionids. On the basis of the maximum-likelihood method of determining the power law luminosity function index, we derive s ≡ 1 + 2.5 log( r) = 1.56 ± 0.06 for the Perseids with m v = +1 to −5, and s ≈ 1.85 ± 0.1 for the Orionids with m v = +2 to −3. These values are somewhat lower than those found by other observers, but we confirm the approximate power law nature of the luminosity functions. Under the assumption that the masses of visual meteors are proportional to a power law function of the luminosities, this implies power law mass functions. If mass is directly proportional to luminosity, we have power law mass functions with the indices s given above.

The Night Sky in October

FULL moon occurs oil October 13d. 13h. 23m. U.T., and new moon on October 27d. 15h. 23m. The following conjunctions with the moon take place: Oct. 18d. 04h., Mars 4° N. ; Oct. 18d. 14h., Saturn 2° N.; Oct. 23d. 07h., Jupiter 0-2° S. ; Oct. 25d. 03h., Venus 4° S. The following occultati ons of stars brighter than magnitude 6 take place: Oct. 3d. 18h. 01-Om., 49 Lib(D) ; Oct. 8d. 18h. 43.5m., 19 Cap(D); Oct. 15d. 02h. 59.2m., µ Cet(D); Oct. 15d. 04h. 10.3m., µ Cet(R); Oct. 15d. 22h. 17.4m., / Tau(D); Oct. 15d. 22h. 58.6m., / Tau(R); Oct. 17d. Olh. 26.5m., Y Tau(R). The times are given for Greenwich and D and R refer to disappearance and reappearance respectively. Mercury attains its greatest western elongation on Oct. 10. It is a morning star, and at the beginning of the month rises at 5h., an hour before sunrise. At the end of the month it rises at 6h. 15m., 35 minutes before sunrise. Venus is a morning star and rises at 3h. 17m. and 2h. 37m. at the beginning and end of the month respectively. The planet attains its greatest brilliancy on Oct. 13. Mars can be seen in the constellation of Taurus in the evening and sets at 12h. 32m. at the beginning of the month and at llh. 05m. at the end of the month. On Oct. 28 the planet is stationary. Jupiter, in the constellation of Leo, is a morning star, rising at Ih. 30m. at the beginning of the month and at midnight at the end of the month. Saturn can be seen close to Mars and is stationary on Oct. 9. At the beginning and end of the month the planet sets at 12h. 40m. and llh. 10m. respectively. Times are given approximately for the latitude of Greenwich. The Orionid meteor shower is due about Oct. 18-21. The radiant is close to the star v Orionis.

The Night Sky in October

THE moon is full on Oct. 5d. 8h. 32m. and new on Oct. 27d. 20h. 9m. There will be an occultation of the first magnitude star α Tauri on October 10, the disappearance as seen from Greenwich taking place at 3h. 16.lm. and the reappearance at 4h. 30.1m., the position angles being 290° and 252° respectively. Lunar conjunctions with the planets will be as follows: Mars on Oct. 5d. 23h., Mars 1° S.; Saturn on Oct. 9d. 4h., Saturn 2°N.; Jupiter on Oct. lid. 4h., Jupiter 5° N.; Venus on Oct. 23d. 17h., Venus 8° S. Mercury is an evening star until Oct. 26 and then becomes a morning star. Venus is an evening star and sets at 18h. 38m. at the beginning and at 18h. 19m. at the end of the month. Mars is a morning star until Oct. 10 when it is in opposition to the sun, and then it is an evening star. At the beginning and end of the month the planet souths at Oh. 41m. and 22h. 6m. respectively. Jupiter is a morning star and crosses the meridian at 4h. 44m. on Oct. 1 and at 2h. 44m. on Oct. 31. Saturn is a morning star, the meridian passages being at 3h. 8m. and 1h. 7.m at the beginning and end of the month respectively. The Orionid meteor shower will commence about Oct. 18 and will continue for a few nights; the radiant point is close to ν Orionis. Comet van Gent (1941d) will be visible with the aid of a small telescope during the month. It will be easily identified, a 3–inch refractor showing it quite distinctly, as its magnitude is about 8.5. The comet is moving northward in declination in the constellation Ursa Major, and on Oct. 19 will be close to ψ Ursaa Majoris. Its distances from the earth and sun in the middle of the month will be nearly the same—about 108 million miles. Although it is receding from the Sun it is still approaching the Earth, for which reason its magnitude will not vary very much during the month, that due to the increase in distance from the Sun being nearly balanced by the change due to the decrease in distance from the Earth. An ephemeris for every four nights is given for the comet. A short ephemeris was given in NATURE of Aug. 2, p. 139.