Meteoric Phenomena Research Articles

Are Meteors a Tool for Studying the Asteroids? Or Vice Versa?

The bulk of the comments I made at the colloquium are to be found in two recent papers (McCrosky and Ceplecha, 1970; McCrosky et al., 1971). The following summary is offered in place of a full text.Most interpretations of all meteor data rely on knowledge of the relationship (luminous efficiency) between mass and luminosity. Discussions of recent experiments made to determine the luminous efficiency are found in papers by Ayers et al. (1970) and Becker and Friichtenicht (1971). Faint meteor phenomena can be understood if the meteoroids are weak, low-density (pm ≈ 0.25 g/cm3) “fluff balls” such as can be expected on the basis of Whipple's comet model (Jacchia, 1955; Jacchia et al., 1967). Alternative explanations, not requiring low densities, have been offered. Jones and Kaiser (1966) propose thermal shock of strong, high-density material as a fragmentation mechanism. Allen and Baldwin (1967) and Baldwin and Allen (1968) have reanalyzed Jacchia's data in terms of phenomena observed in the laboratory in simulated reentry experiments. Here, a high-density meteoroid froths and thereafter behaves as a low-density body. They also revise the luminosity law to account for blackbody radiation of refractory material. McCrosky and Ceplecha (1970) show that neither of these alternative explanations can apply to large bodies and, using photographic observations of bright fireballs, they defend Jacchia's original proposal for all meteors.

7. Meteor spectra (survey paper)

Meteor luminosity is frequently used for the computation of meteor mass. This procedure is a rough approximation only if the spectral distribution of the light energy and its changes during the meteor flight are not known. A good-quality photograph of a meteor spectrum includes much more information on the meteor phenomenon than any other method can provide. There is of course a stronger limitation by meteor brightness than for direct meteor photography. Detailed spectral analysis is available for meteors 4 or 5 magnitudes brighter than for those photographed directly. This could be the reason that meteor spectroscopy is not applied to a desirable extent for the study of meteor phenomenon.

CONCERNING IONOSPHERIC TURBULENCE AT THE METEORIC LEVEL

Booker [see 1 of “References” at end of paper] and Booker and Cohen [2] have given reasons for thinking that application of fluid mechanics to meteoric phenomena leads to results in discord with previous thought. This has led to a discussion [3] that is continued in this paper. An underlying feature of the discussion is a phenomenon that may be described as the rough trail paradox. This arises from the fact that the turbulence velocity of the large eddies is about ten times greater than the turbulence velocity of the small eddies. For a trail that has been rendered rough by the small eddies, let us examine the echoes from two points, separated by a distance of the order of the large eddy size. Due to the motion of the large eddies, interference between these two points is taking place at a rate ten times faster than the rate at which the phase of the echo from either point is taking up random values due to the motion of the small eddies. The upshot is that, as already mentioned by Booker [1], the most obvious features of the fading of long-duration meteor echoes are controlled by the motion of the large eddies even when the mechanism of return is backscattering associated with the small eddies. Failure to appreciate this point seems to have led Manning and Eshleman [3] to claim as an antithesis to the Kolmogoroff-Heisenberg theory of turbulence results that, in fact, are consistent with it.

The Circular Normal Distribution: Theory and Tables

(1953). The Circular Normal Distribution: Theory and Tables. Journal of the American Statistical Association: Vol. 48, No. 261, pp. 131-152.

A comet model. I. The acceleration of Comet Encke

view Abstract Citations (678) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A comet model. I. The acceleration of Comet Encke Whipple, F. L. Abstract A new comet model is presented that resolves the chief problems of abnormal cometary motions and accounts for a number of other cometary phenomena. The nucleus is visualized as a conglomerate of ices, such as H,O, NH3, CH4, CO, or CO, (C,N,?), and other possible materials volatile at room temperature, combined in a conglomerate with meteoric materials, all initially at extremely low temperatures (<50 K). Vaporization of the ices by externally applied solar radiation leaves an outer matriz of nonvolatile insulating meteoric material. Quantitative and qualitative study shows that heat transfer through tiiin meteoric layers in a vacuum is chiefly by radiation, that the heat transfer is inversely proportional to the effective number of layers, and that an appreciable time lag in heat transfer can occur for a rotating cometary nucleus. Because of the time lag, such a cometary nucleus rotating in the "forward" sense will emit its vaporized ices with a component toward the antapex of motion. The momentum transfer from the kinetic velocity of the emitted gas will propel the nucleus in the forward sense, reduce the mean motion, and increase the eccentricity of the orbit. Such orbital effects occur for Comet D'Arrest; the mean daily motion of Comet Wolf I also appears to be decreasing. Retrograde rotation can produce an acceleration in mean motion and a decrease in eccentricity, as observed for Comet Encke. If the decelerating force component is taken as its maximum theoretical value, the present observed acceleration in the mean motion of Comet Encke can be produced by a loss of 0.002 of its mass per revolution. The corresponding mass loss for Comet D'Arrest is 0.005. For both comets the observed changes in eccentricity are obtained if the force acts proportionately to the solar energy flux but is cut off at a solar distance of about 2 A.U. A second paper (Part II) soon forthcoming will be concerned with the physical problems of comet structure, loss of meteoric and gaseous material, and correlations with observed meteoric phenomena. Publication: The Astrophysical Journal Pub Date: March 1950 DOI: 10.1086/145272 Bibcode: 1950ApJ...111..375W full text sources ADS | Related Materials (3) Commentary: 1999ApJ...525C.393B Part 2: 1951ApJ...113..464W Part 3: 1955ApJ...121..750W

Some Practical Aspects of Meteoritics

AbstractIt is believed that a thoroughgoing program of research on meteorites and meteoric phenomena would yield knowledge of a practical nature. Some of the areas of life in which meteoritical research may prove of value are: weather forecasting, the lighting industry, mineral deposits, metallurgy, aëronautics, ballistics, and radio.

Our Astronomical Column

MAY METEORS.?Meteoric phenomena are usually somewhat scarce in May, but fireballs are often more abundant than in other months. The chief display of shooting stars, next perhaps in importance to the Aquarids of Halley's Comet, is a shower radiating from a position eastwards of Corona and near Herculis at about 247o + 290. They are swift white meteors of average magnitude and moderately short paths, and have been most plentifully observed on about May 18 and 24, but further observations are required to determine the epoch of maximum. Fireballs are occasionally recorded from Scorpio and from the western region of Aquila in May, and a few very slow-moving meteors are seen in some years from near Capella. Although the meteors visible at this time of the year are not equal in number to those appearing on autumn nights, they are of considerable interest, and have never been sufficiently observed. The bulk of the observations in this department of astronomy has been accumulated in the last half of the year, and it follows that many of the meteoric systems visible in the spring season have been comparatively neglected.

Meteoric Phenomena, February 7-22

Meteoric Phenomena, February 7-22

Our Astronomical Column

THE METEOR SEASON.—Mr. Denning writes:—“There is a special season for many things, and meteors have their more favourable times and periods. Astronomers generally regard the months of August and November as the particular dates when meteors are abundantly displayed. There is substantial ground for this idea. August and November are memorable as having been the months of occasional brilliant exhibitions of meteors in the modern past. In more ancient times July and October were the favoured months by the same meteoric systems, which have slowly advanced in their dates owing to changes in astronomical conditions. To the regular observer the meteoric season may be said to open at about the middle of July, when there occurs a decided increase in the visible number of meteors contemporary with the first oncoming of the Great Perseid shower. We may usually observe twice as many meteors during the last half of July as in the first half. This is not wholly due to the activity of two or three special showers, but is partly attributable to a general increase in meteoric phenomena. July often affords a most agreeable recompense to the observer in supplying plenty of interesting objects, and this is always appreciated after their rarity in preceding months. Thus in June, 1915, at Bristol, only thirty-six meteors were seen in watches of the sky extending over 202 hours, a degree of scarcity which I never remember to have previously experienced. The Perseids ought to be splendidly witnessed this year with suitable weather about August 9-13. The path of the larger meteors should be carefully recorded, also the time when the maximum number of meteors is visible.”

November Meteor-showers

THE early part of November does not present anything very noteworthy as regards meteoric phenomena, which may be said to begin about November 9, the following being the principal meteor-showers of the month:—

Our Astronomical Column

A REMARKABLE METEORIC PHENOMENON.—In No. 4503 of the Astronomische Nachrichten Dr. Max Wolf describes a curious phenomenon observed on May 22, at about nh. 49m. (Königstuhl M.T.), at Heidelberg. A faint meteor, pursuing a 4° path obliquely from east to west, passed over the star υ Aquike with great velocity; its breadth was about 15′, and it left a faint trail, which disappeared immediately. But although this trail was only momentarily visible, the star remained invisible for at least 3.5 seconds, its light apparently cut off by the material left behind by the evanescent meteor.

Meteoric Phenomena in June

Meteoric Phenomena in June

Leonid Meteors, 1902. A Forecast

THE historical interest which attaches to the Leonid star showers naturally renders the near approach of mid-November a subject of paramount importance to meteor observers. Nor is expectation lessened on the present occasion by the moderate though somewhat unexpected brilliance of the Leonid display witnessed last year in America on the morning of November 15. The question must naturally occur to many, will there be a revival of the phenomenon in the November of 1902, and if so, will it make its appearance in a less or a more intensified form than in the previous year? Generally speaking, the prospects of a star shower on the night of November 15 this year are very good. An analysis made by the writer of the conditions under which last year's shower appeared, and also of those connected with the more brilliant meteoric spectacles of the past, shows that the event of November 15, 1901, is likely to be much surpassed by the meteoric phenomenon of 1902. The display falls due on the night of November 15 on the present occasion, and not on that of November 14 as was the case last year and was duly predicted by the writer (Daily Chronicle, November 14), though the maximum occurred somewhat later on that night than had been expected. The first phase of the shower will take place, however, at an hour not very well suited for its observation in western Europe, the time of its maximum being November 15d. 10h. 45m. G.M.T., when the radiant will be not much more than just above the horizon. Meteors from a radiant in full activity as it emerges above the horizon afford an interesting spectacle, however, and though their numbers must in consequence be seriously diminished, they somewhat atone for their paucity by often long and rapid flights across the heavens. This first appearance of the shower will of course be best observed in places situated at least a few hours to the east of Greenwich, though it ought not to escape observation in our less favoured localities. This early display promises to vie in brilliancy with that observed on the western slopes of the Pacific in 1901, if atmospheric conditions turn out favourable in those places best suited for its observation on the night of November 15, and in all places where the radiant will be above the horizon at the time of its maximum it ought to render shooting stars pretty abundant during the early hours of that night.

The Auroral “Meteoric Phenomena” of November 17, 1882

IF Dr. Groneman has established the fact that the spindleshaped beam from every point of observation appeared moving in a straight line, that is an important point gained; but I fail to gather from his letter on p. 388 that there is clear evidence of this. He cites S. H. Saxby as one observer in favour of this, but his description appears to me very ambiguous. When he says, “Its trajectory was much flatter than that of the stars,” what stars does he mean? If he means the stars at the same declination as that of the beam, viz. about 10° S., then a great circle undoubtedly would be flatter, but still more would a small circle having its centre at the magnetic pole. On the other hand, H. D. Taylor writing from near York describes the path of the beam us from south-east to south-west, thus making it a small circle curved in the wrong direction for an auroral arch.

The Auroral “Meteoric Phenomena” of November 17, 1882

IT is much to be desired that the increasing interest concerning this great phenomenon should supply the only way of obviating the paucity and incompleteness of observations, by having a meeting of observers and advanced nature-students either at London or Bristol. The Utrecht observation says: “When this arch had obtained the length of 90° (which lasted only a few seconds), a separation was made in the middle of its length,” &c. I think this accounts for many of the discrepancies.

A Waterspout

AMONG the meteoric phenomena of which we have heard recently, not the least interesting occurred on Thursday the 14th near the Kelston Round Hill, about three miles to the west of Bath. Shortly after five o'clock in the evening the inhabitants of the village of Weston, which lies between Kelston Hill and Bath, were startled, by a volume of water advancing like a tidal wave along the Kelston Road; in a minute the water was upon them, flooding the houses and laying the main street four feet deep under water; with such force did it come that a stone weighing five hundred-weight was carried several yards, while smaller ones were taken a much greater distance.

Remarks on professor Olmsted's theory of the meteoric phenomenon of November 12th, 1833, denominated shooting stars, with some queries towards forming a just theory

Remarks on professor Olmsted's theory of the meteoric phenomenon of November 12th, 1833, denominated shooting stars, with some queries towards forming a just theory

Remarks on Professor Olmsted's theory of the meteoric phenomenon of November 12th, 1833, denominated shooting stars, with some queries towards foming a just theory

Remarks on Professor Olmsted's theory of the meteoric phenomenon of November 12th, 1833, denominated shooting stars, with some queries towards foming a just theory

Remarks on Professor Olmsted's theory of the meteoric phenomenon of November 12th, 1833, denominated shooting stars, with some queries towards forming a just theory

Remarks on Professor Olmsted's theory of the meteoric phenomenon of November 12th, 1833, denominated shooting stars, with some queries towards forming a just theory

Remarks on Professor Olmsted's theory of the meteoric phenomenon of November 12th, 1833, denominated shooting stars, with some queries towards forming a just theory

Remarks on Professor Olmsted's theory of the meteoric phenomenon of November 12th, 1833, denominated shooting stars, with some queries towards forming a just theory