scholarly journals 46. The structure of the solar chromosphere from centimetre-wave radio observations

1957 ◽  
Vol 4 ◽  
pp. 263-268 ◽  
Author(s):  
J. P. Hagen
Keyword(s):  
Wave Length ◽  
Outer Part ◽  
Wave Radiation ◽  
Solar Chromosphere ◽  
The Sun ◽  
Radio Waves ◽  
Visible Radiation ◽  
Short Radio Wave ◽  
Wave Radio ◽  
Image Position

The atmosphere of the sun is transparent to visible radiation, is nearly transparent to millimetre and centimetre radio radiation, and becomes opaque to the metre and longer wave radiation. Information about the chromosphere can then be given by observing the radiation from the sun at short radio wave-lengths. In its outer part, the atmosphere of the sun is highly ionized. Absorption in any region is directly proportional to the square of the density and the wave-length squared and inversely to the temperature to the three-halves power This is the familiar equation for the absorption of radio waves in an ionized medium. By consequence of this, the longer wave radiation is absorbed in the outer layers of the sun's atmosphere and can escape only from these outer regions. The shorter wave-length radiation is absorbed very little in the outer part of the solar atmosphere where the density is quite low, and hence radiation from the chromosphere escapes as centimetre and millimetre radio waves. In fact, the principal radiation from the sun in the centimetre and millimetre region comes from the chromosphere.

scholarly journals 79. Radio emission from the moon and the nature of its surface

1957 ◽  
Vol 4 ◽  
pp. 406-407 ◽  
Author(s):  
V. S. Troitzky ◽  
S. E. Khaikin
Keyword(s):  
Radio Emission ◽  
Attenuation Coefficient ◽  
Wave Length ◽  
Degree Of Polarization ◽  
Lunar Phase ◽  
Radio Waves ◽  
The Moon ◽  
Subsolar Point ◽  
Image Position ◽  
Academy Of Sciences

A theoretical study of the integral radio emission of the moon, measured at the wave-length of 3·2 cm. (Zelinskaja and Troitzky[1]; Kajdanovsky, Turusbekov and Khaikin[2]), was carried out at the Gorky radio astronomical station ‘Zimenky’ and at the Physical Institute of the Academy of Sciences of the U.S.S.R. The following expression for the average radio temperature of the entire lunar disk, as a function of the lunar phase, Ωt, was obtained (Troitzky, 1954) [3]: Here tan ξ = δ/(1 + δ) and δ = β/κ, where β is the attenuation coefficient of the thermal wave, κ the power attenuation coefficient of the radio wave. Further, Tm = 374°K. is the temperature of the subsolar point, Tn is the temperature at the lunar midnight, Θ = Tm – Tn and k0 is the reflexion coefficient of radio waves for vertical incidence (k0 ≈ 0–1). The numerical coefficients in equation (1) were obtained as a result of averaging the Fresnel reflexion coefficients over the whole disk. The degree of polarization of the total radio emission was calculated and was found to be about 4 %.

2. On the Rotation of the Plane of Polarization by Quartz, and its relation to Wave-Length

1882 ◽  
Vol 11 ◽  
pp. 815-818 ◽  
Author(s):  
W. Peddie
Keyword(s):  
Wave Length ◽  
Angular Rotation ◽  
Light Rays ◽  
Image Position ◽  
Polarization Of Light

The angular rotation of the plane of polarization of light-rays in their passage through quartz is a function of the wave-length, and is roughly represented by the formulawhere A is a constant depending on the quartz. This formula is only approximate, however, and one object of the experiments described below was to ascertain how closely the rotation might be represented by three terms of the equation

scholarly journals The Bakerian lecture —Regularities and irregularities in the ionosphere—I

1937 ◽  
Vol 162 (911) ◽  
pp. 451-479 ◽  
Keyword(s):  
Specific Conductivity ◽  
Wave Length ◽  
Ground Level ◽  
Short Wave ◽  
The State ◽  
Total Conductivity ◽  
The Sun ◽  
Magnetic Studies ◽  
Short Wave Length ◽  
Radio Measurements

Our knowledge concerning the state of the atmosphere lying above about 80 km. in height has been derived from experiments on radio wave reflexion as well as from studies of terrestrial magnetism and of the aurora. The information derived from radio experiments is, fortunately, in the nature of a supplement to, rather than a duplicate of, information derivable in other ways. As one of the best examples in this connexion may be mentioned the question of electrical conductivity. Here the magnetic studies of Schuster and Chapman yield an estimate of the total conductivity for currents travelling horizontally, whereas the radio measurements give the state of ionization at different levels from which the specific conductivity at those levels may be estimated. One of the most striking things about the ionosphere is the marked solar control. Speaking generally it may be said that the ionization increases and decreases as the sun rises and sets. Again, speaking generally, we may say that the main part of the ionization is caused by solar-violet light. The rays from the sun meet the outer layers of the atmosphere first and the short wave-length radiation is absorbed there, causing ionization. It thus comes about that the study of the ionosphere becomes the study of an interesting part of the sun's spectrum which cannot be detected at ground level. It also becomes the study of certain atomic processes such as photo-ionization, recombination of ions and attachment of electrons to neutral molecules such as cannot be investigated at very low pressure in the laboratory, because of the influence of the walls of the vessel confining the gas.

3. On the Radiant Spectrum

1869 ◽  
Vol 6 ◽  
pp. 147-149 ◽  
Author(s):  
David Brewster
Keyword(s):  
The Sun ◽  
Image Position ◽  
Small Image

I have given the name of Radiant Spectrum to a phenomenon which I discovered in 1814, and which I described to this Society in the early part of that year.It will be understood from fig. 1, which represents the brilliant radiation which surrounds a very small image of the sun, when it is formed either by reflection or refraction, or otherwise.

scholarly journals Solar Spike Suggests a More Active Sun

Eos ◽  
2019 ◽  
Vol 100 ◽  
Author(s):  
Nola Redd
Keyword(s):  
Magnetic Field ◽  
The Sun ◽  
Radio Waves ◽  
The Magnetic Field

Radio waves are providing a new way to probe the Sun and suggest that the magnetic field of its corona may be stronger than long thought.

scholarly journals Solar spectral irradiance variability of some chromospheric emission lines through the solar activity cycles 21-23

2017 ◽  
pp. 71-86
Author(s):  
Ü.D. Göker ◽  
M.Sh. Gigolashvili ◽  
N. Kapanadze
Keyword(s):  
Solar Activity ◽  
Chemical Elements ◽  
Wave Length ◽  
Spectral Lines ◽  
Spectral Irradiance ◽  
Close Connection ◽  
Solar Chromosphere ◽  
Solar Spectral Irradiance ◽  
Activity Cycles ◽  
Solar Activity Cycles

A study of variations of solar spectral irradiance (SSI) in the wave-length ranges 121.5 nm-300.5 nm for the period 1981-2009 is presented. We used various data for ultraviolet (UV) spectral lines and international sunspot number (ISSN) from interactive data centers such as SME (NSSDC), UARS (GDAAC), SORCE (LISIRD) and SIDC, respectively. We reduced these data by using the MATLsoftware package. In this respect, we revealed negative correlations of intensities of UV (289.5 nm-300.5 nm) spectral lines originating in the solar chromosphere with the ISSN index during the unusually prolonged minimum between the solar activity cycles (SACs) 23 and 24. We also compared our results with the variations of solar activity indices obtained by the ground-based telescopes. Therefore, we found that plage regions decrease while facular areas are increasing in SAC 23. However, the decrease in plage regions is seen in small sunspot groups (SGs), contrary to this, these regions in large SGs are comparable to previous SACs or even larger as is also seen in facular areas. Nevertheless, negative correlations between ISSN and SSI data indicate that these variations are in close connection with the classes of sunspots/SGs, faculae and plage regions. Finally, we applied the time series analysis of spectral lines corresponding to the wavelengths 121.5 nm-300.5 nm and made comparisons with the ISSN data. We found an unexpected increase in the 298.5 nm line for the Fe II ion. The variability of Fe II ion 298.5 nm line is in close connection with the facular areas and plage regions, and the sizes of these solar surface indices play an important role for the SSI variability, as well. So, we compared the connection between the sizes of faculae and plage regions, sunspots/SGs, chemical elements and SSI variability. Our future work will be the theoretical study of this connection and developing of a corresponding model.

scholarly journals Galactic and extra-galactic radio frequency radiation due to sources other than the thermal and 21-cm emission of the interstellar gas

1958 ◽  
Vol 5 ◽  
pp. 37-43
Author(s):  
R. Hanbury Brown
Keyword(s):  
Thermal Emission ◽  
Wave Length ◽  
Black Body ◽  
Interstellar Gas ◽  
Ionized Gas ◽  
Radio Frequency Radiation ◽  
The Galaxy ◽  
Image Position ◽  
Galactic Radio ◽  
Frequency Radiation

At wave-lengths greater than about one metre the majority of the radio emission which is observed from the Galaxy cannot be explained in terms of thermal emission from ionized interstellar gas. This conclusion is widely accepted and is based on observations of the equivalent temperature of the sky and the spectrum of the radiation. The spectrum at metre wave-lengths is of the general form: where TA is the equivalent black-body temperature of a region of sky and A is the wave-length. The exponent n varies with direction but lies between about 2·5 and 2·8, and is thus significantly greater than the value of 2·0 which is the maximum to be expected for thermal emission from an ionized gas. Furthermore the value of TA is about 1050 K at 15 m and thus greatly exceeds the electron temperature expected in H 11 regions.At centimetre wave-lengths it is likely that the majority of the radiation observed originates in thermal emission from ionized gas; however, the present discussion is limited to a range of wave-lengths from about 1 m to 10 m where the ionized gas in the Galaxy is believed to be substantially transparent and where the origin of most of the radiation is believed to be non-thermal.

scholarly journals VII. Note on 'spectroscopic papers'

1879 ◽  
Vol 29 (196-199) ◽  
pp. 166-168
Keyword(s):  
Royal Society ◽  
Wave Length ◽  
The Sun ◽  
Decimal Point ◽  
The Earth

In a recent communication to the Royal Society, Mr. Lockyer has criticised our statement of Young’s wave-length identifications of certain chromospheric lines. As to the wave-length, we have throughout our table omitted all figures after the decimal point merely for the sake of not cumbering the table. The numbers, Young tells us, are not his own, but taken from Ǻngström’s catalogue. Moreover, as to Young’s identifications with metallic lines, he states expressly that they were taken from the maps of Kirchhoff, Ǻngström, and Thalén, and Watts’s “Index of Spectra.” But our object was not to criticise Young’s work, but only to use it for the purpose of comparing the behaviour of certain metals on the earth and in the sun, and the conditions under which certain lines appear, or do not appear, or are reversed.

scholarly journals Observations of Solar Continuum Emission at Decameter Wavelengths

1990 ◽  
Vol 142 ◽  
pp. 513-514
Author(s):  
Ch. V. Sastry
Keyword(s):  
Electron Temperature ◽  
Brightness Temperature ◽  
Large Scale ◽  
Continuum Emission ◽  
The Sun ◽  
Temperature Variations ◽  
One Dimensional ◽  
Wave Radio ◽  
Grating Interferometer ◽  
The Continuum

We observed the continuum emission from the radio sun when there is no burst activity at λ = 8.7 m with the large decameter wave radio telescope at Gauribidanur (Latitude 13° 36‘ 12“ N and 77° 27‘ 07“ E) with a resolution of 26'/40'. A compound grating interferometer with one dimensional resolution of 3' is also used. These observations are made during August 1983 and June 1986. The brightness temperature at the center of the sun varied from 0.2 106 K to 0.8 106 K during these periods on time scales of several hours to a day. Since the sun is absolutely quiet during these periods we believe that the radiation is purely thermal in nature. In this case the observed brightness temperature variations imply large scale density variations by more than a factor of three if the corona is optically thin at these wavelengths. Alternatively if the corona is optically thick the observations imply real electron temperature variations with or without accompanying density variations.

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