Observations of the 7 March, 1970 total solar eclipse at wavelengths of 3.2 and 8.3 mm

The 7 March, 1970 total solar eclipse was observed at wavelengths of 3.2 and 8.3 mm; the object being to use the knife edge of the Moon as it passed across the Sun to improve angular resolution on the Sun. This in turn would provide a radial brightness distribution of the Sun with an angular resolution of a few seconds of arc.Excellent eclipse curves were obtained at 3 mm; however, some external interference marred the 8 mm record near totality.The 8 mm brightness distribution is subject to some uncertainty, but tends to show limb brightening. The 3 mm brightness distribution shows a well defined complex limb brightening within about 1 arc min of the optical limb. The maximum brightening is approximately 30% above the average disc temperature.     

Brightness distributions of the Sun at 33 and 37 GHz

The brightness distributions of the Sun were observed at 33 and 37 GHz. Maximum limb brightening of about 10% was observed at both frequencies.     

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.     

The coarse structure of the solar atmosphere

Observations of the quiet sun at wavelengths from 3 Å to 75 cm show (with two exceptions: the Ovi line at 1032 Å and possibly the continuum at 1.2 mm) either no limb brightening or less than had been supposed. On the other hand, the brightness temperature is observed to increase with wavelength in the millimeter and centimeter range. If this increase is due to greater visibility of hot overlying material, that material ought to be evident at the limb at shorter wavelengths, resulting in limb brightening. The only possible explanation for the absence of limb brightening at almost all wavelengths is that the emitting surface is rough at all wavelengths, with a scale of roughness approximately equal to the scale height at each temperature. Contradictions with existing models, along with the additional observations required for an improved model are discussed.     

Motions and mass changes of a persistent coronal streamer

A coronal streamer was observed by the white light coronagraph on Skylab during 5 successive limb passages between 1 June, 1973 and 6 August, 1973. The Skylab data give independent measures of coronal brightness and polarization, as functions of time. These permit the distinction between changes in the coronal streamer's appearance due to solar rotation and actual structural changes. The streamer's visual appearance changed slightly between successive limb passages indicating that it was not a steady state feature. Measurements of the streamer's latitude, brightness, and polarization during 3 east limb passages show that: (1) the streamer's axis migrated southward from 25° N at first east limb passage to 11° N at second east limb passage to 8° N latitude at third east limb passage; (2) the streamer's mass (and mass gradient with height), varied by between 20 and 50% from one east limb passage to the next; (3) the streamer's longitudinal extent was also observed to be less on successive east limb passages; and (4) mass changes (distinct from coronal transients) occurring over hours were detected during at least two limb passages. Comparison of the outer coronal observations with observations from lower in the solar atmosphere indicate that the streamer was associated with a complex of solar activity consisting of active regions and filaments. This complex of activity shifted southward by the same amount as the streamer. The variations detected in the streamer preclude the detailed determination of its three-dimensional structure.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

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.     

Solar limb brightening and enhancement measurements at 1.2 mm

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.     

1997年3月9日日全食8.6mm波段射电观测

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％．     

Observations of the 1.4mm brightness distribution of the sun

Observations of the 1.4 mm center to limb solar brightness distribution show that there is little, if any, limb brightening at this wavelength. Knowledge of the antenna radiation pattern is vital in interpreting the radio measurements.This work was supported by the U.S. Air Force under Contract No. F04701-70-C-0069.     

The radio brightness of the undisturbed outer solar corona in the presence of a radial magnetic field

The radio brightness of the quiet outer solar corona at a frequency of 35 MHz in the presence of a radial magnetic field is computed. It is found that the brightness temperature of the ordinary radiation increases significantly. It is also found that in the presence of a radial magnetic field, coronal holes will appear as bright emission regions on the disk and as depressions at the 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.     

H-Alpha survey of the solar corona at Pic-du-Midi

A daily survey of cool material evolution in the inner parts of the solar corona is now performed at the Pic-du-Midi observatory with an H imaging coronagraph. The total field of the coronagraph allows the detection of emission regions all around the solar limb, up to 0.6 solar radius above the limb. This survey is devoted to the study of coronal events and mass motions in a large range of spatial and time scales. The observing modes are associated with a set of numerical treatment processes to produce images which are calibrated in intensity relative to the solar brightness. Position angles and height above the solar limb of the coronal features are determined. Methods of calibration, sky brightness subtraction, and detection of events are discussed.     

Variations of Magnetic Bright Point Properties with Longitude and Latitude as Observed by Hinode/SOT G-band Data

Small-scale magnetic fields can be observed on the Sun in high-resolution G-band filtergrams as magnetic bright points (MBPs). We study Hinode/Solar Optical Telescope (SOT) longitude and latitude scans of the quiet solar surface taken in the G-band in order to characterise the centre-to-limb dependence of MBP properties (size and intensity). We find that the MBP’s sizes increase and their intensities decrease from the solar centre towards the limb. The size distribution can be fitted using a log–normal function. The natural logarithm of the mean (μ parameter) of this function follows a second-order polynomial and the generalised standard deviation (σ parameter) follows a fourth-order polynomial or equally well (within statistical errors) a sine function. The brightness decrease of the features is smaller than one would expect from the normal solar centre-to-limb variation; that is to say, the ratio of a MBP’s brightness to the mean intensity of the image increases towards the limb. The centre-to-limb variations of the intensities of the MBPs and the quiet-Sun field can be fitted by a second-order polynomial. The detailed physical process that results in an increase of a MBP’s brightness and size from Sun centre to the limb is not yet understood and has to be studied in more detail in the future.     

Model-independent restoration of the brightness distribution across the disks of stars from high precision eclipsing light curves

Estimates are made of the accuracy with which the brightness distributions across the disks of stars can be reconstructed through analysis of data from high precision space-based photometry of classical eclipsing systems and observations of the transit of planets across stellar disks. The ill-posed reconstruction problem was solved on a compact set of monotonically nonincreasing, upwardly convex, non-negative functions. One of the difficulties with this method in the case of stars with thin photospheres is the poor convergence of the solution at the point where the brightness distribution has a discontinuity at the edge of the star's disk. Nevertheless, the use of this method for analysis of high precision observational data is justified, since it can be used to obtain an estimate of the limb darkening that is independent of any model assumptions. The reconstructed brightness distribution for the star HD 209458, for which the transit of a planet over its disk was observed with the HST space telescope, is in good agreement with the results of a nonlinear model fit. Translated from Astrofizika, Vol. 51, No. 4, pp. 595–606 (November 2008).     

Photometry of Venus: II. Theoretical brightness distribution over the disk

Theoretical brightness distributions over the Venus disk have been computed for homogeneous and multilayered cloud models. With homogeneous models, the relative brightness does not depend very much on the optical properties of the cloud, except near the limb or for small phase angles. For multilayered cloud structures, the relative brightness is nearly fixed by the structures and the relative brightness is nearly fixed by the scattering function of the uppermost cloud; the vertical distribution of the absorption is unimportant if the spherical albedo of the planet is given. If the horizontal inhomogeneities currently seen on Venus are due to a layered structure, with an optical thickness of the upper cloud varying from point to point, large simplifications seem possible, and measured contrasts at various wavelengths should permit a test of such a model.     

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.     

Observation of the 1997-03-09 total eclipse at 8.6 mm

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.     

A method for investigating the brightness distribution near the solar limb at millimeter wavelengths

The brightness distribution near the solar limb has been investigated by means of a technique in which derivatives of drift scans of the Sun were compared with derivatives of drift scans of the Moon. The results obtained at 88.3 GHz (3.4 mm) indicate that the Sun is limb neutral within the uncertainty of our measurement. If limb brightening or darkening is present, it represents less than 1.6 % or 1.2 %, respectively, of the total power received from the Sun at this wavelength.     

The Brightness Temperature of the Quiet Solar Chromosphere at 2.6 mm

The absolute brightness temperature of the Sun at millimeter wavelengths is an important diagnostic of the solar chromosphere. Because the Sun is so bright, measurement of this property usually involves the operation of telescopes under extreme conditions and requires a rigorous performance assessment of the telescope. In this study, we establish solar observation and calibration techniques at 2.6 mm wavelength for the Nobeyama 45 m telescope and accurately derive the absolute solar brightness temperature. We tune the superconductor–insulator–superconductor (SIS) receiver by inducing different bias voltages onto the SIS mixer to prevent saturation. Then, we examine the linearity of the receiver system by comparing outputs derived from different tuning conditions. Furthermore, we measure the lunar filled beam efficiency of the telescope using the New Moon, and then derive the absolute brightness temperature of the Sun. The derived solar brightness temperature is \(7700 \pm 310~\mbox{K}\) at 115 GHz. The telescope beam pattern is modeled as a summation of three Gaussian functions and derived using the solar limb. The real shape of the Sun is determined via deconvolution of the beam pattern from the observed map. Such well-calibrated single-dish observations are important for high-resolution chromospheric studies because they provide the absolute temperature scale that is lacking from interferometer observations.     

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.