The 3.3-mm brightness distribution of the quiet sun

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.     

The brightness distribution of the sun at 2.8cm wavelength

Maps of the Sun at 2.8 cm wavelength, observed with the 100-m telescope in Effelsberg, on 1972, October 31 and 1973, February 10, are discussed. The brightness distribution over the Sun is, with the exception of active regions, approximately constant and nearly sharp-edged. Regions of small enhancements in the radiation can be identified with zones of weak activity in the solar magnetograms. Optical filaments could also be seen in absorption at 2.8 cm wavelength, the optical depth being of the order of 0.2. Several active regions have been analysed with respect to their position relative to their optical counterparts and to their brightness temperature: The latter was found to reach almost 10⁶K in one case. No noticeable limb brightening could be observed; if any exists, it should be smaller than 5%. Likewise no noticeable elliptical deformation of the Sun's disk could be found. The geometrical thickness of the coronal layer, contributing to the undisturbed radiation at 2.8 cm was estimated to be a maximum of 4000 km.     

Solar brightness distribution at 8.6 mm from interferometer observations

The radial brightness distribution of the quiet Sun at 8.6 mm is synthesized from observations using a sixteen element east-west interferometer in Nagoya. The observed brightness is flat from the disk center to 0.8R . A slight darkening appeared between 0.8R and the limb. No evidence of the bright ring near the limb is found. The radio radius at 8.6 mm is 1.015±0.005R . In addition there exists a coronal component just outside the radio limb.     

Interferometer observations of the solar brightness distribution at 8.6 mm wavelength

The brightness distribution of the quiet Sun at 8.6 mm wavelength is synthesized from off-meridian observations using an eight element east-west interferometer with a maximum base line of 16.38 m (1913). The observed brightness distribution is practically flat from the disk center to the optical limb. The effective radius of the nearly uniform component is 1.01 R . If the limb brightening is present, the brightening located between 0.95 R and 1.01 R , and the total flux density of the limb brightening is less than 1% of the total flux density of the Sun. In addition to the nearly uniform component there exists a coronal component just outside the optical limb.     

Comments on the quiet Sun brightness distribution at 1.2 mm wavelength

A re-analysis of the brightness distribution of the quiet Sun at 1.2 mm wavelength is made. It is concluded that there is no evidence for uniform or limb-brightened distribution at this wave-length.     

Planetary brightness temperature measurements at 1.4-mm wavelength

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.     

Solar brightness distribution at 3mm wavelength from observations of the eclipse of 1976 October 23

Observations of the Sun were made at 3 mm wavelength during the total eclipse of 1976 October 23. Analysis of the record obtained near third contact indicates that the Sun at this wavelength is slightly limb-brightened, and that the solar radius is 1.007 times the photospheric radius.     

Planetary brightness temperature measurements at 8.6 mm and 3.1 mm wavelengths

New measurements of the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn at 3.1 and 8.6 mm wavelengths are given. The temperatures reported for the planets at 3.1 mm wavelength are higher than previous measurements in this wavelength range and change the interpretation of some planetary spectra. For Mercury, it is found that the mean brightness temperature is independent of wavelength and that a temperature dependent thermal conductivity is not required to match the observations. In the case of Mars, the spectrum is shown to rise in the millimeter region as simple models predict. For Jupiter, the need to recalculate the spectrum with recent models is demonstrated. The flux density scale proposed by Dent (1972) has been revised according to a more accurate determination of the millimeter brightness temperature of Jupiter.     

The quiet sun brightness temperature at 408 MHz

The flux of the radio quiet Sun and the brightness temperature at 408 MHz (73 cm) are derived from measurements with the E-W Nançay interferometer and the E-W arm of the Medicina North Cross. It is shown that the lowest envelopes, which defined the radio quiet Sun, correspond to transits of extended coronal holes across the disk of the Sun.     

The sky brightness when the rising sun is in eclipse

Part of the “Xia-Shang-Zhou Chronology Project” is the study of a historical record of “double dawn” and its astronomical interpretation. We used the light meter on ordinary cameras to determine the sky variation during normal sunrises and sunsets, set up a way of calculating the variation when the rising sun is in eclipse, and identified the range and intensity of the double dawn phenomenon. For this, we organized a mass participation of the observation of the 1997-03-09 eclipse in Xinjiang Province. The observations are in good agreement with our model calculation and prove that an eclipsed sunrise could indeed give rise to the phenomenon of “double dawn”     

Further evidence for a complex limb structure in the solar radial brightness distribution at mm wavelengths

A computer program to convolve numerically any azimuthally symmetric, solar radial brightness distribution with standard antenna patterns of small half power beamwidths has been used to find a solar brightness distribution which is a good fit to the eclipse curve obtained during the 7 March 1970 partial solar eclipse with the NRAO 36-ft antenna at 3.5 mm. This brightness distribution is compared with the brightness distribution at 3.2 mm determined by the Pennsylvania State University Radio Astronomy Observatory group during the same eclipse but observed from Mexico where totality occurred. The two brightness distributions are very similar in shape, showing a double peak near the limb, but differing slightly in the positions of the peaks.     

Active region flare rates and 8.6 mm brightness temperatures

The relationship between the flaring rates and 8.6 mm brightness temperatures of active regions has been analyzed. We find that as the 8.6 mm brightness temperature of an active region increases, a larger proportion of the energy released by the region in the form of flares is contained in progressively larger flares. At all temperatures subflares are the most frequent event. At intermediate and high temperatures about 10% of the events are flares of importance 1 or larger with flares of importance 2 or larger contributing an increasing fraction of these events as the brightness temperature increases.     

Brightness temperatures of the quiet sun and new moon at the 6 mm wavelength

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.     

Longitudinal distribution of PCA sources on the sun

For 181 PCA's recorded during the years 1956–1969 the association with flares is studied. Both the number of events which cannot be associated with any flare on the visible hemisphere, as well as the longitude distribution of identified proton flares, lead to the conclusion that 25–30% of PCA's are caused by flares behind the western solar limb. PCA's of this kind are mostly small. During the investigated years no PCA > 13 dB and possibly no PCA > 8.5 dB were caused by flares behind the limb, while hardly 60% of PCA's < l dB had their origin on the visible hemisphere. While the sources of GLE's and of PCA's in general, are centered around 50°W which corresponds to the average curvature of the magnetic field lines in interplanetary space, the strongest PCA's (> 8.5 dB) show an anomalous longitude distribution centered around ∼ 20°W. It is suggested that this anomaly may be a consequence of the fact that in strong PCA events the kinetic energy density of protons below 100 MeV becomes comparable to the magnetic energy density in space, thus leading to a ‘straightening’ of the magnetic field lines.     

The distribution of interstellar extinction near the sun

Photometric data inuvbyß system from 3713 stars is used to map the distribution of colour excesses up to 500 parsec from the Sun, producing diagrams for a series of layers aligned with the galactic plane. Individual clouds are detected, with a mean diameter of 6 parsecs, while cloud complexes have a mean diameter of 100 pc. From the maps it seems that the interstellar medium near the Sun presents regions of non-negligible extinction, while the Sun itself is enbedded in a diffuse cloud, or slightly off its border. The large scatter in the distribution ofE(b-) is confirmed, with a mean extinction ofA _v=0 _. ^m 38 up to 500 pc.     

The bimodal spiral galaxy surface brightness distribution

We have assessed the significance of Tully and Verheijen's bimodal Ursa Major Cluster spiral galaxy near-infrared surface brightness distribution, focusing on whether this bimodality is simply an artefact of small number statistics. A Kolmogorov–Smirnov style of significance test shows that the total distribution is fairly represented by a single-peaked distribution, but that their isolated galaxy subsample (with no significant neighbours within a projected distance of ∼80 kpc) is bimodal at the 96 per cent level. We have also investigated the assumptions underlying the isolated galaxy surface brightness distribution, finding that the (often large) inclination corrections used in the construction of this distribution reduce the significance of the bimodality. We conclude that the Ursa Major Cluster data set is insufficient to establish the presence of a bimodal near-infrared surface brightness distribution: an independent sample of ∼100 isolated, low-inclination galaxies is required to establish bimodality at the 99 per cent level.     

The dependence of brightness distribution on the inclination of galaxies

A sample of 92 galaxies with published surface photometric data inB band and inclined randomly to the line of sight is selected and used to compute the photometric parameterQ _N . The dependence ofQ _N on the apparent flatteningq is found and discussed for different morphological groups.Q _N is more sensitive toq in earlier-type galaxies.     

Observations of global oscillations of the sun in the SOKOL experiment onboard the CORONAS-PHOTON satellite

The helioseismological experiment onboard the CORONAS-PHOTON satellite is intended for the study of characteristics and the internal structure of the Sun using the solar eigenmodes spectrum obtained by the measurement of fluctuations of the solar radiation intensity. This experiment is the continuation of investigations of solar global oscillations started onboard artificial satellites CORONAS-I and CORONAS-F. Measurements of fluctuations of the solar radiation intensity in seven optical ranges—from the near ultraviolet to infrared spectral regions—are carried out by the solar photometer SOKOL (SOlnechnye KOLebaniya (Solar Oscillations)) developed at IZMIRAN. Over an instrument operation period of more than 9 months, a large volume of the scientific information (more than 500 MB) has been obtained. The primary processing of obtained data was performed, and spectra of fluctuations of the solar radiation intensity were constructed. On the basis of part of the processed information obtained by the photometer SOKOL, and data of the experiment DIFOS (Differential Oscillations of the Sun) onboard the artificial satellite CORONAS-F, the dependence of the relative amplitude of oscillations on the wavelength of the observation was determined.