Search

Measuring the solar diameter at all position angles gives the complete figure of the Sun. Their asphericities have implications in classical physics and general relativity, and the behavior of the optical systems used in the direct measurements is to be known accurately. A solar filter is a plane-parallel glass with given absorption, and here we study the departures from the parallelism of the faces of a crystal slab 5 mm thick, because of static deformations. These deformations are rescaled to the filter's dimensions. Related to the Solar Disk Sextant experiment and to the Reflecting Heliometer of Rio de Janeiro a simplified model of the influences of the inclination between the external and the internal surfaces of a glass solar filter, is discussed., Comment: 4 pages, 2 figures, presented at the PT5 parallel session of the XIV Marcel Grossmann Meeting of General Relativity, Sapienza University of Rome, on 17 July 2015

The interest on the solar diameter variations has been primary since the scientific revolution for different reasons: first the elliptical orbits found by Kepler in 1609 was confirmed in the case of the Earth, and after the intrinsic solar variability was inspected to explain the climate changes. The CCD Solar Astrolabe of the Observat\'orio Nacional in Rio de Janeiro made daily measurements of the solar semi-diameter from 1998 to 2009, covering most of the cycle 23, and they are here presented with the aim to evidence the observed variations. Some instrumental effects parametrizations have been used to eliminate the biases appeared in morning/afternoon data reduction. The coherence of the measurements and the influence of atmospheric effects are presented, to discuss the reliability of the observed variations of the solar diameter. Their amplitude is compatible with other ground-based and satellite data recently published., Comment: 13 pages, 7 figures, submitted to Solar Physics

The figure of the Sun reflects its inner structure and dynamics, influencing also the perihelion precession of close orbiting bodies, like Mercury. To study the solar figure from ground, the deformation on the solar image induced by the atmosphere has to be known up to one part over a million, and this is done through differential refraction models: a historical review of them is drafted. The solar oblateness has been investigated in order to validate alternative theories to General Relativity and to understand the internal dynamics of our star. The solar figure should possess only micro departures from sphericity according to the standard stellar structure theory and helioseismology data, though variations along the cycle has been observed. Ground-based and satellite data show contrasting observational results. The oblateness measured onboard RHESSI satellite, the one of SDS onboard a stratospheric ballon and that one of the Astrolabe of Rio de Janeiro are presented with their implications in classical and relativistic gravitation. The perspectives offered by the reflecting heliometer in the future measurement of the oblateness are depicted., Comment: 14 pages, 8 color figures, proceedings of VI IWARA Meeting, Rio de Janeiro 30 sept - 3 oct 2013, CBPF. To appear in SLAC eConf/C1309292

Monitoring the micro-variations of the solar diameter helps to better understand local and secular trends of solar activity and Earth climate. The instant measurements with the Reflecting Heliometer of Observatorio Nacional in Rio de Janeiro have minimized optical and thermal distortion, statistically reducing air turbulence effects down to 0.01 arcsec. Contrarily to satellites RHRJ has unlimited lifetime, and it bridges and extends the measures made with drift-scan timings across altitude circles with 0.1 arcsec rms with Astrolabes. The Astrolabe in Rio operated from 1998 to 2009 to measure the solar diameter and the detected variations have statistical significance., Comment: 1 page, 1 figure. Proceedings of LARIM XIV Latin American Regional IAU Meeting, Florianopolis 25-30 November 2013

Out of the three quantities that characterize the state of an isolated gaseous body: pressure, temperature and volume the radius is the only one directly measurable for the Sun, what is specially true in the optical window and for ground base measurements. The Heliometer of Observatorio Nacional, in Rio de Janeiro, measures the distance between two opposite limbs of the Sun in the same field of view, through the reflection on a 10 cm parabolic mirror split on its half and forming an appropriate angle. This configuration is free from optical aberrations and focal variations along the measurement direction. The mirrors are made on CCZ vitro-ceramic and the telescope structure is of carbon steel, resulting that there is no flexion or temperature deformation. The instrument is compact, and can perform hundreds of measurements per duty day, around all heliolatitudes. It attains an accuracy on the solar radius of 0.01 arcsec, becoming the ideal instrument to monitor from the ground the solar diameter, and to bridge satellites and astrolabes historical series of data. We discuss the first years of regular observation, with emphasis on the instrumental calibrations and on the statistic study of the derived time series, attitude series, and solar geometry series. On basis of these series we obtain how well the Heliometer and Solar Astrolabe results are matched., Comment: 2 pages, 2 figures, accepted for ICRC 2013 conference, Rio de Janeiro 2-9 July 2013

From 1997 the Observatorio Nacional has been observing the Sun with an astrolabe in order to study variations on the solar semi-diameter. Till now more than 20.000 observations were done. The observations taken in the year of 2001 were special because, for the first time, they can be compared with other equivalent series, and because the Sun passed by a second maximum of its cycle of activity. The observed data were at first selected, by leaving out the values relative to unsuccessful measurements. We dealt with the errors in the observed values originating from the instability of the objective prism, which increases the east values and diminishes the west ones. Then, it was possible to remove the errors by comparing the East and West series. Next, the observational conditions were investigated: the air temperature, the Fried's parameter, and the dispersion on the solar limb adjustment. Their influence on the results was accounted for. Finally we considered the errors arising from leveling defects, modeled by a dependence to the azimuth of observation. All the corrections are smaller than the standard deviation and the mean semi-diameter values stay unaffected. This means that the series have the same pattern with smaller deviations. After the correction of the prism instability the East and West series become more similar, what reinforces that they aim at the same target. The corrected series were compared with other observations of solar semi-diameter from the CERGA, Cote d'Azur Observatory in France and from Tubitak Observatoty in Antalya, Turkey. The comparison reveals alike features, which deserve further, detailed study. Also, the series was compared to the daily mean Sun spots number. It exhibited three maxima along 2001, that coincide on time with three maxima of the correct series delayed by 50 days. Again, this requires a further study., Comment: 72 pages, 33 figures in color. Projeto Final de Curso para a Obtencao do Titulo de Astronomo Universidade Federal do Rio de Janeiro - Maio 2004, Language: Portugues

From 1998 to 2003 the CCD Solar Astrolabe of the Observatorio Nacional in Rio de Janeiro made more than 20000 observations of the Solar Semidiameter. In the present work similar corrections for the observational results of 2002 and 2003 were determined. Initially, the values have been corrected in function of their mean quadratic offset to the local trend averages, therefore without modifying the measured variations. Finally, the values have been corrected for the bias, using coefficients obtained from the correlation between some observational parameters and the observational measures. Then the total series was compared with series of pointers of the solar activity. The hypothesis of variation of the semidiameter tied to the solar activity was examined through the correlations between the different pairs of pointers. Strong correlations between some pairs were obtained. Next, the same correlations were obtained now considering time delays of one series in relation to the other. Several pairs have shown an increase on the correlation, indicating the presence of a significant phase shift between them. For the pair solar semidiameter and irradiance the mode of the phase for maximum correlation was calculated for two distinct cases: either for the complete series of data, or leaving off the data relative to the epochs of the two summits of the solar activity cycle. The comparison shows that the solar semidiameter responds closely to variations of irradiance in the conditions where the peaks of activity are considered; inversely, it precedes the variations of irradiance, by at least one hundred days, when the peak values are discarded, thus indicating the existence of two distinct regimes. We also studied how the semidiameter of the Sun varies throughout its latitudes. It was noted that each band of latitude has a different response, even so there is a global variation in time., Comment: 147 pages, 95 figures in color. Tese de Mestrado apresentada ao Programa de Pos-Graduacao do Observatorio do Valongo como parte dos requisitos necessarios a obtencao do titulo de Mestre em Astronomia da Universidade Federal do Rio de Janeiro. Dezembro 2005. Language: Portugues

The solar astrolabe at Observatorio Nacional has been doing a series of solar semidiameter measurements, extending from 1998 up to 2009, to a total of 21640 observations of the Sun. Using the data series it was established the solar radius variation along that period, as well as determining results about the change of the solar ellipticity. To the work in perspective, the measurements of the solar radius in the past four centuries are reviewed, followed by a more detailed account of the contemporaneous measurements. The deviations of the observed values from the true values caused by observational and instrumental effects are studied and the strategies used to derive the corresponding corrections are shown. The relationships linking the variation of the semidiameter and the relevant indexes of the solar activity are analyzed. Finally, the time series from Observatorio Nacional was enchained to all the other similar astrolabe series, from which the data were graciously confided to this work. Using such much longer combined data set it was established the long term behavior of the solar semidiameter along the last three solar cycles. The outcome is a strong correlation to the long period features of the solar activity described by the annual mean of sunspots count. Putting together the long term semidiameter variation and other solar evidences we point out the near approach of a deep minimum of sunspots., Comment: 159 pages + 152 of appendix data, 114 figures. PhD Thesis in Astronomy, Observatorio Nacional, Rio de Janeiro, 1st March 2011. Language: Portuguese

The heliometer of Fraunhofer in Koenigsberg (1824) is a refractor in which the lens is split into two halves to which is applied a linear displacement along the cut. Later in 1890s a variation of the heliometer has been realized in Goettingen using a beam splitting wedge: these methods were both subjected to chromatic and refractive aberrations; the second configuration being much less affected by thermal fluctuations. The mirrored version of the heliometer conceived at the Observatorio Nacional of Rio de Janeiro overcome these problems: the two halves of the vitrified ceramic mirror split at a fixed heliometric angle produce the two images of the Sun exempt of chromatisms and distortions. The heliometer of Rio is a telescope which can rotate around its axis, to measure the solar diameter at all heliolatitudes. A further development of that heliometer, now under construction, is the annular heliometer, in which the mirrors are concentric, with symmetrical Point Spread Functions. Moreover the location of the Observatory of Rio de Janeiro allows zenithal observations, with no atmospheric refraction at all heliolatitudes, in December and January., Comment: 6 pages, 3 figures, 1 table; proc. of the XII Italo Korean Meeting on Relativistic Astrophysics, 4-8 July 2011, Pescara, Italy. To appear in Nuovo Cimento B