Star Scintillations Research Articles

Relation Between the Structure of Stellar Shadow Band Patterns and Stellar Scintillation

Difficulties are encountered in attempting to obtain an instantaneous picture of the pattern of stellar shadow bands seen on the surface of a telescope objective. There is a close statistical relationship between these patterns and the scintillation of the total starlight received. By observing scintillation through a diaphragm having two holes with variable separation between them one can derive the Fourier spectrum of periodicities in the shadow pattern and the autocorrelation function of the pattern. A number of patterns and associated autocorrelation functions are illustrated. Some remarks are then made on the correlation between the scintillation of close double stars and the influence of telescope aperture upon it. Finally the analysis is generalized to show how a frequency analysis of the scintillation can yield a space-time autocorrelation function.

The scintillation of radio stars

The intensity and apparent position of radio sources are observed to fluctuate in a manner analogous to the scintillation of visual stars. Experiments are described which show that the scintillation is caused by diffraction of the incoming waves by irregularities of electron density in the upper ionosphere. The origin of the irregularities is not known and the solution may raise problems of astronomical interest. A phenomenon similar to scintillation occurs when a radio source is viewed through the solar corona, and this fact enables deductions to be made about the irregular structure of the corona at distances in the range 5–15 solar radii.

Winds in the ionosphere

The evidence for the existence of winds in the ionosphere is now manifold. It is partly directly visual, from the motion of luminous meteor trails and high luminous night clouds and patchiness in the night airglow. It is partly based on inference from indirect observations, such as the geomagnetic variations at the earth's surface; these are ascribed to electric currents partly flowing in the ionosphere, which are explained by dynamo action of ionospheric motions. Another type of indirect observational evidence is provided by the scintillation of radio stars. The most abundant and varied evidence, however, is afforded by inference from observations in which human experiment also plays a vital part, namely by the transmission of radio beams to the ionosphere and their reception after they have been modified by passage through that region, either solely by the influence of ionospheric motion, or by the fleeting presence there of ionized meteor trails.

F-scatter at Huancayo, Peru, and relation to radio star scintillations

The scattering of radio waves by the F-region of the ionosphere at an equatorial location (Huancayo, Peru) was discussed by Booker and Wells (1938). Subsequent analysis reveals pronouncedly diurnal, seasonal, and annual characteristics. It is fundamentally a nighttime event, with greatest frequency of occurrence in the period from four hours before midnight to four hours after midnight. The scattering is most prevalent during seasons when the sun is overhead and is infrequently observed during May, June, July, and August (local winter) when the noon solar zenith angle becomes as great as 35°. The relative total annual occurrence of F-region scatter for the period 1938 through 1945 shows low values during 1941–1942, followed by a rapid increase through 1946, which is not closely related to solar activity. The diurnal properties of F-scatter closely correspond to reported characteristics of radio star scintillations with peak activity around midnight. However, the annual or seasonal properties are not in simple agreement.

Scintillation of Stars and the Atmosphere

Scintillation of Stars and the Atmosphere

A new radio interferometer and its application to the observation of weak radio stars

A new type of radio interferometer has been developed which has a number of important advantages over earlier systems. Its use enables the radiation from a weak 'point’ source such as a radio star to be recorded independently of the radiation of much greater intensity from an extended source. It is therefore possible to use a very much greater recorder sensitivity than with earlier methods. It is, in addition, possible to use pre-amplifiers at the aerials, and the resolving power which may be used is therefore not restricted by attenuation in the aerial cables. Besides improved sensitivity, the new system has a number of other advantages, particularly for the accurate determination of the position of a radio source. Unlike earlier systems the accuracy of position finding is not seriously affected by rapid variations in the intensity of the radiation. It also has important applications to the measurement of the angular diameter and polarization of a weak source of radiation. The new system has been used on wave-lengths of 1⋅4, 3⋅7, 6⋅7 and 8 m for the detection and accurate location of radio stars, and for the investigation of the scintillation of radio stars. It has also been used in a number of special experiments on the radiation from the sun. The results which have been obtained in these experiments have confirmed the advantages predicted analytically.

Some Experiments on the Scintillation of Stars and Planets

Some Experiments on the Scintillation of Stars and Planets

Scintillation of radio stars during aurorae and magnetic storms

During aurorae, the scintillations of radio stars are, on the average, four times more rapid than during normal conditions. This increase in the scintillation rate is believed to result from a fourfold increase in the steady drift motion of the ionospheric irregularities which cause the scintillations. More generally, it is found that the scintillation rate, and the velocity of the ionospheric irregularities, are approximately proportional to the K index of geomagnetic activity.

A Diffraction Theory of the Scintillation of Stars on Optical and Radio Wave-Lengths

A review of current theories of the scintillation of stars on optical wavelengths shows that the refraction theory of scintillation requires excessive atmospheric density gradients, and fails to explain the observed scintillation in colour, whilst the physiological explanations are insufficient to explain all the observed phenomena. A new theory, in which the scintillation phenomena are attributed to Fresnel diffraction at a non-homogeneous atmospheric layer, is shown to explain the observed effects, and to require considerably smaller density gradients. A similar theory, taking into account the. effect of a wave-length change of × 10 7 , is shown to explain the observed fluctuations in intensity of radio waves from the localized extra-terrestrial sources of radio noise.

A DIFFRACTION THEORY OF THE SCINTILLATION OF STARS ON OPTICAL AND RADIO WAVE-LENGTHS

A review of current theories of the scintillation of stars on optical wavelengths shows that the refraction theory of scintillation requires excessive atmospheric density gradients, and fails to explain the observed scintillation in colour, whilst the physiological explanations are insufficient to explain all the observed phenomena. A new theory, in which the scintillation phenomena are attributed to Fresnel diffraction at a non-homogeneous atmospheric layer, is shown to explain the observed effects, and to require considerably smaller density gradients. A similar theory, taking into account the effect of a wave-length change of 107, is shown to explain the observed fluctuations in intensity of radio waves from the localized extra-terrestrial sources of radio noise.

Photo-electric Observations of the Scintillation of Stars

IN a recent article on the “Scattering of Electromagnetic Waves by Atmospheric Turbulence”1, Dr. E. C. S. Megaw points out that a study of the scintillation of stars is also a study of the average properties of turbulence in the atmosphere. He reviews the rather scanty observational data that are available on the subject. It is in this connexion that some records of stellar scintillation, that have been made recently with a photo-cell at Dunsink Observatory, and which extend the observed upper frequency-limit of the light fluctuations to about 500 cycles a second, may be of interest.

The scintillation of stars.

IN a recent communication in Nature1, Dr. A. H. R. Goldie has suggested that the scintillation of stars may be associated with waves at an interface between two currents of air which have a difference of temperature of the order of 5–7° F. “Such waves,” he writes, “should not uncommonly have an amplitude of the order of up to 500–1,000 ft. at the interface, wave-length up to 10 miles or more, speed anything up to 40 ft. per sec., but probably usually lower.”

The Scintillation of Stars

How the heart of the astronomer would rejoice if the scintillation of stars were due, as Prof. Hartridge1 considers possible, to physiological causes rather than to non-homogeneity of the earth's atmosphere! It is the practice of many observing astronomers, before ‘opening up’, to look at the sky and note, on some estimated scale, (i) the degree of clearness or transparency of the sky, and (ii) the degree of steadiness or goodness of seeing. (i) may be judged (in the absence of strong moonlight) by the limiting magnitude of stars just visible to the eye at various altitudes, and is important, in the case of photography, for judging exposure times; (ii) may be judged by the scintillation-frequency of the brightest stars; the greater the frequency the worse the ‘seeing’ will be. On the very best nights the stars appear nearly steady, the occasional winking being slow and infrequent. Such nights are suitable for measuring close binaries, the Airy disks and their diffraction ring systems appearing steady, often for many seconds together; on such nights, also, the finest planetary details are to be seen. When scintillation is conspicuous and rapid, the images of stars, viewed through a telescope, appear larger than the Airy disks and show a rapidly changing and uneven distribution of illumination. If the telescope is put out of focus, the star will appear as an illuminated disk showing, on a steady night, a number of fine concentric rings as in a ‘zone plate’. On an unsteady night, rings are no longer visible, the whole disk appearing to ‘boil’. It has been noted by British astronomers that both the scintillation and the telescopic images of stars are, in general, worse when the wind is in the east. Planets are only observed to scintillate when viewed at a low altitude on a night of exceptionally bad seeing.

The Scintillation of Stars

Hartridge and Weale1 advance evidence for a physiological explanation of the scintillation of stars. I have made a simple observation which seems to contradict this. Sirius, seen through a misted car window, appeared as a large area of diffuse blue-white light, subtending perhaps five degrees: this light fluctuated markedly and at roughly the same frequency as the star seen through an unobscured area of the window. The effect was more readily seen when looking twenty or thirty degrees away from the star, but could be seen by direct observation.

The Glaciation of Brazil.—Scintillation of Stars

A VERY cursory examination of the gneiss rocks about Rio de Janeiro—particularly the Corcovado—will show how the rock breaks up. In some places it comes off in great flakes like the coats of an onion, and the edges of these flakes are quite friable, and can be reduced to fine grains between the fingers. In many places it is found quite crumbled up by the weather, and down the coast towards Santos fine grains of these rocks can be found in the soundings at some distance from the land.

Further Researches on the Scintillation of Stars

SINCE last we reviewed M. Montigny's valuable researches on the scintillation of stars (vol. xviii. p. 292) he has again published some highly interesting details. The researches now in question refer specially to the changes of colour which characterise the scintillation of the red and orange stars. M. Montigny tried to solve the question whether the changes of colour in scintillation follow certain definite laws; whether, for instance, their relative frequency expressed in numbers, shows differences which depend on the nature of the star's own light, on the star's elevation above the horizon, or on the condition of the atmosphere.

Scientific Serials

Poggendorff's Annalen der Physik und Chemie, No. 10.—This number contains several papers of great interest: the first is by G. Quincke, on electric currents resulting from the non-simultaneous insertion of two mercury-electrodes into different liquids. The author bases his experiments upon those of St. Claire Deville and Troost, who found it probable that platinum absorbs hydrogen or other gases when being heated in a gas or alcohol flame, and then shows a different electric action towards water and dilute acids from that of platinum that has not been so heated. The paper contains a minute description of the apparatus used and tables of the results obtained; in an appendix the author treats of the relation between capillary and electrical phenomena, referring to G. Lippmann's paper (Pogg. Ann., vol. 149, p. 556), from whom he materially differs.—Experiments made with a magnetised copper wire, by Prof. Balfour Stewart and Dr. A. Schuster.—On the chemical action of the solar spectrum upon haloid salts of silver, by H. W. Vogel. Chloride, bromide, and iodide of silver, are not only sensitive towards the highly refrangible rays of the spectrum, but also towards the less refrangible ones, although in a much smaller degree; their sensitiveness does not only depend upon their optical power of absorption of the respective rays, but also upon the absorption power of other substances they may be mixed with. Coloured substances which assist the photographic reduction process and absorb certain spectral rays, highly increase the sensitiveness of the silver salt towards the absorbed rays; thus the sensitiveness of silver salts for red, yellow, and green rays can be greatly augmented. Certain colourless bodies are found to have a similar action. The light reflected from pigments shows a very different effect from that of spectral colours, on account of the varying optical composition of artificial colours and their smaller intensity.—On the question of velocity of magnetic action at distances, by H. Herwig; investigations relating principally to terrestrial magnetism. It is found that this velocity is at least half a million geographical miles (or about 2K millions of English miles) per second; in other words, that at any given spot on the surface of the earth terrestrial magnetism becomes fully active in less than the 300th part of a second.—On a modification of the magneto-electric revolution experiment, by the same.—On comparison of electric machines, by Mr. Mascart. The author describes experiments made to ascertain the actual quantity of electricity produced by eleven different machines in a given time and under the same conditions.—On the measuring of the electromotive power of voltaic piles in absolute units, by A. Crova.—The frequency of changes of colour in the scintillation of stars is generally related to the spectrum they show, by C. Montigny. Stars that twinkle strongly show few spectral lines, while those with little scintillation have many bands and lines in their spectra. —On the theory of organ-pipes, by H. Schneebeli.—Is the application of the vis viva justified in the mechanical theory of heat? by H. Fritsch. The author answers this question in the negative.—On induction-effects in magnets of different hardness, by L. Külp.