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1.
F. I. Shimabukuro 《Solar physics》1970,12(3):438-446
Center-to-limb brightness distribution measurements of the quiet Sun at a wavelength of 3.3 mm show that there is a slight
limb brightening at this wavelength. Within the measurement accuracy of the system used, the limb brightening function is
only radially dependent. At 3.3 mm, the measurements are consistent with a solar brightness curve that is flat to about r = 0.8 with a rapid increase to a peak value of about 1.3 at the limb. The results show that most of the central disk 3.3-mm
emission comes from a thin layer of relatively constant temperature about 1500–3500 km above the photosphere.
This work was supported by the U.S. Air Force under Contract No. F04701-69-C-0066. 相似文献
2.
Observations of the planet Saturn at wavelengths of 49.5 and 94.3 em are reported. The equivalent disk brightness temperatures were found to be 400 ± 65°K and 540 ± 110°K, respectively. It is suggested that the enhanced portion of the spectrum of the disk brightness temperature favours the idea that the observed long wavelength radiation comes from the planet's atmosphere.However, the possibility of a magnetic field associated with Saturn is not rejected by the observations. Part of the excess temperature could be attributed to weak synchrotron emission coming from a region outside the ring system. 相似文献
3.
We describe the technique and results of modelling the solar radio emission during the maximum phase of the solar eclipse
of March 29, 2006 on the RATAN-600. The aim of modelling is to refine the brightness temperature of the solar corona at the
distances up to two solar radii from the center of the optical disk of the Sun. We obtained the distribution of brightness
temperature in the vicinity of the coronal hole above the solar North Pole at the wavelength of 13 cm. The results of modelling
showed that brightness temperatures of the coronal hole at the distances greater than 1.02 RC (here RC is the radius of the optical disk of the Sun) is substantially lower than the expected average brightness temperature of
a typical coronal hole, and that of the quiescent Sun (below 30000 K) at the wavelength of 13 cm. The classical Baumbach-Allen
formula for electron density in a spherically symmetric corona agrees with the results of observations starting at distances
of (1.4–1.5) RC. 相似文献
4.
E. E. Reber 《Solar physics》1971,16(1):75-86
Absolute brightness temperatures and brightness temperature ratios of a quiet region near the center of the solar disk and the central region of the new moon were measured simultaneously at the 6 mm wavelength. The measured quiet sun/new moon brightness temperature ratios and reported central brightness temperatures of the new moon confirm the measured brightness temperature of the quiet sun at the 6 mm wavelength.Reported central brightness temperatures of the new moon are tabulated and graphed as a function of frequency and wavelength. The equation of a linear regression line for the reported measurements is given for estimating the brightness temperature of the new moon at any millimeter wavelength. Estimated brightness temperatures of the new moon and measured quiet sun/new moon ratios are used to estimate solar brightness temperatures at several millimeter wavelengths. The solar brightness temperatures, the regression line, and the Van de Hulst theoretical model are presented graphically as a function of frequency and wavelength. The regression line equation is given for estimating solar brightness temperatures at any wavelength in the 6 to 1 mm wavelength interval and is solved for the wavelength of the measured ratios.Reported solar brightness temperatures in the millimeter wavelength region are tabulated. The measured temperatures in the 6 to 1 mm wavelength interval and a linear regression line are presented graphically as a function of frequency and wavelength. The regression line equation is given and solved for the solar brightness temperatures at the 6 mm wavelength.This work supported by the U.S. Air Force under Contract No. F04701-69-C-0066. 相似文献
5.
１９９７年３月９日日全食８．６ｍｍ波段射电观测资料的分析表明：８．６ｍｍ波段射电太阳的半径为１．０１２Ｒ,总流量为２５４０ｓｆｕ（１ｓｆｕ＝１０－２２Ｗ／ｍ２Ｈｚ）,日面平均亮温度为９６３２Ｋ,径向亮温度分布,在日面光学边缘内侧０．９３６－０．９９２Ｒ处,存在临边增亮,平均增亮幅度相对于日面中心为９．７％． 相似文献
6.
We report observations of the solar radio radius at wavelengths between 1.2 and 11 cm performed with the Bonn 100 m-telescope. In combination with former measurements of the centre-to-limb variation of the solar brightness these observations are discussed in terms of atmospheric models. We consider the solar disk to be covered by arches at low latitudes, while at the poles coronal holes are located. The temperature dependence on height is taken from EUV-line intensities, hydrostatic equilibrium is adopted, spicules are assumed to be responsible for the relatively low brightening. The interpretation of our measurements demands certain values of the brightness temperature of spicules as a function of wavelength within a modest interval. 相似文献
7.
We present high-resolution interferometry of Uranus at 6 cm wavelength and single-dish observations of the disk-averaged brightness temperature, TB, at 2.8 and 4.8 cm wavelength. The 1978 measurements of TB of 228 ± 2,243 ± 9, and 259 ± 4 K at 2.8, 4.8, and 6 cm, respectively, support the finding of M. J. Klein and J. A. Turegano (1978, Astrophy. J.224, L31–L34) that the brightness temperature of Uranus has been rising. There is no evidence for radio emission from outside the visible disk at 6 cm. Radiation from a synchrotron radiation belt or from the Uranian rings is certainly less than 10% of the total radio flux. The interferometry shows a possible 55 ± 20 K difference in brightness temperature between the equator and the currently exposed pole. The pole appears to be ～275 K while the equator is ～220 K. However, a permanent gradient of this magnitude is insufficient to account for the rise in disk-averaged brightness by simple reorientation of Uranus' globe relative to our line of sight. The changing insolation probably triggers a redistribution of the trace constituent NH3 which is responsible for the radio opacity. The NH3 may be interacting strongly with H2S on Uranus. 相似文献
8.
Precise relative measurements of the disk brightness temperatures of Venus, Mars, Jupiter, and Saturn have been made at a mean wavelength of 1.4 mm. The rings of Saturn contribute significantly to the observed total emission. Other results include a better understanding of the properties of the NRAO 11-m antenna near its high frequency limit and of atmospheric degradation of observations in this wavelength range. 相似文献
9.
《Chinese Astronomy and Astrophysics》1999,23(2):237-243
COPY THE ORIGINAL Analysis of the total eclipse observation of 1997 March 9 at wavelength 8.6 mm, shows that, at this wavelength, the solar radius is 1.012 R⊙, the total flux density is 2540 sfu, the mean brightness temperature of the solar disk is 9632 K, and the brightness temperature distribution shows limb brightening at the inner edge of the solar disk, the average brightness at 0.936−0.992 R⊙ being 9.7% above the central brightness. 相似文献
10.
We report on observations of the full Moon brightness temperature covering the frequency range of 300-950 GHz, and also on observations of the lunar eclipse of July 16, 2000, though only covering the frequency range of 165-365 GHz due to poor atmospheric transmission at higher frequencies. All observations were performed from the summit of Mauna Kea (HI) using a Fourier Transform Spectrometer mounted on the Caltech Submillimeter Observatory and supplemented by measurements of the atmospheric opacity using a 183 GHz Water Vapor Monitor. The telescope was pointed to the center of the lunar disk (with a footprint of ∼45-15 km on the Moon at 300 through 900 GHz). In order to obtain the correct values of the Moon brightness temperatures at all frequencies we carefully corrected for the atmospheric absorption, which varies across the submillimeter domain. This correction is fully described. The measured pre-eclipse brightness temperature is around 337 K in the 165-365 GHz range. This temperature slightly increases with frequency to reach ∼353 K at 950 GHz, according to previous broader band data. The magnitude of the temperature drop observed during the eclipse at 265 GHz (central frequency of the band covered) was about ∼70 K, in very good agreement with previous millimeter-wave measurements of other lunar eclipses. We detected, in addition, a clear frequency trend in the temperature drop that has been compared to a thermal and microwave emission model of the lunar regolith, with the result of a good match of the relative flux drop at different frequencies between model and measurements. 相似文献
11.
We discuss the possible contribution of the thermal cyclotron radiation from hot coronal magnetic loops to the observed characteristics of the microwave emission from solar active regions. Based on the simplest three-dimensional model of a loop in the shape of a hot torus, we have calculated the expected peculiarities of the frequency and polarization structures of microwave emission sources associated with sunspots and containing coronal loops. Our model calculations of the two-dimensional brightness temperature distributions at various wavelengths for the ordinary and extraordinary modes and the wavelength dependences of the brightness temperatures are presented in the first part of the work. The loop size, the electron density, and the source position on the disk have been found to affect these characteristics. Our numerical calculations of the brightness temperature distributions and spectra have confirmed the well-known assumption that under certain conditions the spectrum of a hot filament can contain cyclotron lines and the sense of the polarization can change over the range. The results obtained here refer to the brightness temperature along the line of sight that crosses the photosphere at a point with given coordinates, i.e., these are the emission characteristics at a fixed point of the source. Integrated characteristics (the flux from the entire source and its polarization) and a discussion of the hot loop model will be given in the second part of the work. 相似文献
12.
The brightness distribution of the quiet sun on 9.1 cm wavelength is determined from the Stanford pencil-beam radioheliograms for three periods in the recent solar activity minimum, centred at July 15 and September 15, 1964 and at April 5, 1965. The brightness maxima near the limbs are not symmetric with respect to the central meridian, but are situated at 76 °E and 66 °W longitude, respectively. On the disk, the brightness temperature is likewise distributed asymmetrically, but the direction of this asymmetry changes as the new cycle starts. The asymmetries are tentatively explained by assuming the presence of inhomogeneous streamers in the solar atmosphere, which are tilted by the solar rotation. The eastward shift of the limb maxima with respect to the optical disk is confirmed by the 21 cm-heliograms obtained at Fleurs near Sydney, Australia. 相似文献
13.
Stephen J. Keihm 《Icarus》1984,60(3):568-589
A detailed model of the lunar regolith is analyzed to examine the feasibility of an orbital mapping of heat flow using microwave radiometers. For regolith thermal and electrical properties which are representative of Apollo findings, brightness temperature observations in the bandλ = 5–30 cm would be required for heat flow analysis. Spectral variations shortward of 5 cm are controlled primarily by the temperature dependencies of the thermal conductivity and electrical absorption within the diurnal-varying layer. For wavelengths longer than 30 cm, unwanted emission from high impedance subregolith layers can be significant and size limitations on spacecraft radiometers is a factor. Over the 5- to 30-cm band, lunation-averaged brightness temperature increases of 2–10°K are predicted for heat flow values representative of the Apollo measurements. The magnitude of this increase depends directly on the value of regolith microwave absorption. For absorption values consistent with Apollo laboratory measurements, a spectral increase of 5°K is predicted. This value is considered marginally sufficient for an orbital heat flow measurement. However, important non-heat flow effects must be accounted for. Spectral variations can occur due to surface topography and subsurface scattering. For nadir viewing, surface roughness effects are not expected to be significant and topographic effects are nearly constant with wavelength for λ > 5cm. Volume scattering due to subsurface rock fragments can cause emission darkening of 1–6°K. However, spectral variations will not be large unless the distribution of scatterer sizes is sharply skewed. For the Moon, the most serious spurious effect appears to be emissivity variations due to the near-surface density gradient. A brightness temperature decrease of 10°K is predicted from centimeter to decameter wavelengths. If the transition from porous surface fines to compacted regolith soil occurs rapidly (within the upper 3–5 cm), most of the emissivity decrease will occur in the 5- to 30-cm wavelength band. It is recommended that complementary radar measurements be utilized to augment constraints on regolith emissivity and scattering properties. 相似文献
14.
Dennis B. Ward 《Icarus》1977,32(4):437-442
The spectrum of Saturn and its rings between 45 and 115 μm has been measured at an average resolving power of 14 from the NASA Lear Jet. The combined brightness temperature of the rings and planetary disk decreases beyond 65 μm, in disagreement with previous results. A brightness temperature of 65 ± 10°K is obtained for the planetary disk in the 80–110-μm wavelength range if a large-particle, constant-emissivity model is assumed for the rings. The possible effects of small particles in the rings are briefly considered. 相似文献
15.
Solar intensity measurements at a mean wavelength of 1.2 mm were made using a 1.6 m Cassegrain telescope. The measurements included a series of scans made during the partial solar eclipse of May 20th, 1966.A high degree of solar limb brightening is inferred from the measured intensity distribution. The ratio of the disk-averaged brightness temperature to the central brightness temperature at 1.2 mm is calculated to be 1.11 ± 0.02.A fairly intense solar outburst, of approximate duration 50 min, was observed towards the end of the eclipse. 相似文献
16.
Eugene E. Epstein Michael A. Janssen Jeffrey N. Cuzzi William G. Fogarty John Mottmann 《Icarus》1980,41(1):103-118
We have used 3-mm Saturn observations, obtained from 1965 through 1977 and with Jupiter as a reference, to derive a ring brightness temperature of 18 ± 8°K. Thebrightness temperature of the disk of Saturn is 156 ± 9° K. Part of the ring brightness (≈62K) may be accounted for as disk emission which is scattered from the rings; the remainder (12 ± 8° K we attributed to ring particle thermal emission. Because this thermal component brightness temperatures is so much less than the particle physical temperature, limits are placed on the mean size and composition of the ring particles. In particular, as found by others, the particles cannot be rocky, but must be either metallic or composed of extremely low-loss dielectric material such as water ice. If the particles are pure water ice, for example, then a simple slab model and a multiple-scattering model both give upper limits to the particle sizes of ≈ 1 m, a value three times smaller than previously available. The multiple-scattering model gives a particle single-scattering albedo at 3 mm of 0.83±0.13. 相似文献
17.
The combination of seasonal and orbital changes in Martian insolation result in complex latitude dependent surface temperature variations that effect the total radiance of the planet as seen from the earth. These surface temperature variations have been calculated, based upon a computer simulation of the thermal environment of the planet. The temperature variations are then integrated to yield the total radiance of the planet as seen from the earth as a function of time. The absolute radiance of Mars was measured on April 4, 1971, with a balloon-borne radiometer system operating in the wavelength range between 10.5 and 12.5 μm. The average brightness temperature of the Mars disk determined from these measurements was 254°K with a 1 σ error of 4°K. 相似文献
18.
Ch. V. Sastry 《Solar physics》1994,150(1-2):285-294
We have mapped the continuum emission from the undisturbed Sun at a wavelength of 8.7 m during 1981–1985 using the large decameter-wave
radiotelescope at Gauribidanur, India with a resolution of 26 #x00D7; 38 arc min. During the period August 6–30, 1983, the
Sun was exceptionally quiet at meter and decameter wavelengths, and we were able to make maps on several consecutive days.
On these days the position of the centroid of the radio Sun agreed quite closely with the center of the optical Sun indicating
that there is very little or no contribution from active regions. But the observed peak brightness temperature varied from
100 000 to 700 000 K. The half-power widths of the brightness distribution were in the range of 3 to 4R
⊙. The variations of the brightness temperature and the half-power widths are not correlate. It is therefore suggested that
the variations of the brightness temperature are not caused by uniform density variations or due to scattering by an irregular
corona. 相似文献
19.
Titan has been observed with the 5-m Hale telescope at an effective wavelength of 1 mm. Adopting a value of 2700 km for the radius of Titan, we find a brightness temperature of 86±12°K at 1 mm. Comparing our results with previous measurements at longer wavelengths, we conclude that the satellite surface is the source of the 1-mm radiation. Since our measured brightness temperature is close to the equilibrium temperature of a blackbody at the distance of Saturn, we believe there is no significant greenhouse effect on Titan. 相似文献
20.
R.R. Daniel S.K. Ghosh K.V.K. Iyengar T.N. Rengarajan S.N. Tandon R.P. Verma 《Icarus》1982,49(2):205-212
We present far-infrared observations of Saturn in the wavelength band 76–116 μm, using a balloon-borne 75-cm telescope launched on 10 December 1980 from Hyderabad, India, when B′, the Saturnicentric latitude of the Sun, was 4°.3. Normalizing with respect to Jupiter, we find the average brightness temperature of the disk-ring system to be 90 ± 3° K. Correcting for the contribution from rings using experimental information on the brightness temperature of rings at 20 μm, we find TD, the brightness temperature of the disk, to be 96.9 ± 3.5° K. The systematic errors and the correction for the ring contribution are small for our observations. We, therefore, make use of our estimate of TD and earlier observations of Saturn when contribution from the rings was large and find that for wavelengths greater than 50 μm, there is a small reduction in the ring brightness temperature as compared to that at 20 μm. 相似文献