Solar diameter observations with the
Astrolabe at Observatório Nacional - Rio de Janeiro

Jilinski, E. G.; Puliaev, S. P.; Penna, J. L.; Andrei, A. H.; Sinceac, V.; Chollet, F.; Delmas, Christian

doi:10.1051/aas:1998228

Cited by 14 publications

(16 citation statements)

References 8 publications

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“…The program of CCD observations with the astrolabe of Observatório Nacional at Rio de Janeiro for monitoring variations of the apparent diameter of the Sun, has been described by Jilinski et al (1998Jilinski et al ( , 1999. Regular observations started in January, 1997, and they were in progress at least until May 2000.…”

Section: Solar Observations At Rio De Janeiro and Santiagomentioning

confidence: 99%

“…Regular observations started in January, 1997, and they were in progress at least until May 2000. In this astrolabe the small circle of altitude is defined by means of a reflecting prism with a variable angle which permits observations at several zenith distances from about 27 • to 58 • (Jilinski et al 1998). These zenith distances and the latitude of Rio de Janeiro (−22.…”

Section: Solar Observations At Rio De Janeiro and Santiagomentioning

confidence: 99%

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Visual and CCD astrolabe observations of the solar radius

Noel

2001

A&A

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Abstract.Here we discuss and compare two sets of solar semidiameter measurements made with Danjon astrolabes during the period 1997-1999. One is based on 10 522 CCD observations made at Rio de Janeiro, Brazil; the other one is based on 956 visual observations made at Santiago, Chile. Linear fits applied to both data sets give a standard deviation of ±0. 365 and ±0. 360 for each daily mean value of the solar radius for Rio de Janeiro and Santiago respectively. During the period of this analysis, the apparent solar radius had an annual variation of −0. 060 ± 0. 013 according to the CCD observations of Rio de Janeiro and of +0. 213 ± 0. 018 according to the visual observations of Santiago. We show here that this discrepancy could be due to systematic effects, probably of instrumental origin, that produce significant internal inconsistencies in the results of Rio de Janeiro. The drift of the apparent solar radius observed with the astrolabe of Santiago during 1997-1999 is consistent with former results obtained with this instrument since 1990. These results show that the apparent semidiameter of the Sun varies in phase with solar activity (Noël 1997(Noël , 2001).

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Section: Solar Observations At Rio De Janeiro and Santiagomentioning

confidence: 99%

Section: Solar Observations At Rio De Janeiro and Santiagomentioning

confidence: 99%

Visual and CCD astrolabe observations of the solar radius

Noel

2001

A&A

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“…For an observer at the surface of the Earth, the Sun has an angular radius of 0.266 • ± 1.7 % (Jilinski et al, 1998). CST systems have aperture half-angles larger than the angular radius of the solar disc but usually smaller than those of the measuring instruments .…”

Section: Introductionmentioning

confidence: 99%

Can AERONET data be used to accurately model the monochromatic beam and circumsolar irradiances under cloud-free conditions in desert environment?

et al. 2015

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Abstract. Routine measurements of the beam irradiance at normal incidence include the irradiance originating from within the extent of the solar disc only (DNI S ), whose angular extent is 0.266 • ± 1.7 %, and from a larger circumsolar region, called the circumsolar normal irradiance (CSNI). This study investigates whether the spectral aerosol optical properties of the AERONET stations are sufficient for an accurate modelling of the monochromatic DNI S and CSNI under cloud-free conditions in a desert environment. The data from an AERONET station in Abu Dhabi, United Arab Emirates, and the collocated Sun and Aureole Measurement instrument which offers reference measurements of the monochromatic profile of solar radiance were exploited. Using the AERONET data both the radiative transfer models libRadtran and SMARTS offer an accurate estimate of the monochromatic DNI S , with a relative root mean square error (RMSE) of 6 % and a coefficient of determination greater than 0.96. The observed relative bias obtained with libRadtran is +2 %, while that obtained with SMARTS is −1 %. After testing two configurations in SMARTS and three in libRadtran for modelling the monochromatic CSNI, libRadtran exhibits the most accurate results when the AERONET aerosol phase function is presented as a two-term HenyeyGreenstein phase function. In this case libRadtran exhibited a relative RMSE and a bias of respectively 27 and −24 % and a coefficient of determination of 0.882. Therefore, AERONET data may very well be used to model the monochromatic DNI S and the monochromatic CSNI. The results are promising and pave the way towards reporting the contribution of the broadband circumsolar irradiance to standard measurements of the beam irradiance.

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“…Since 1981 the Observatório Nacional/MCT (ON) group makes daily solar observations, in particular, since 1997, aiming to record and study the diameter variations (Jilinski et al, 1998). In 2002 an international network (Réseau de Suivi au Sol du Rayon Solaire -R2S3) was formed to combine the similar work pursued in five countries worldwide (Andrei et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

A solar cycle lengthwise series of solar diameter measurements

et al. 2009

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Abstract. The measurements of the solar photospheric diameter rank among the most difficult astronomic observations. Reasons for this are the fuzzy definition of the limb, the SNR excess, and the adverse daytime seeing condition. As a consequence there are very few lengthy and consistent time series of such measurements. Using modern techniques, just the series from the IAG/USP and from Calern/OCA span more than one solar cycle. The Rio de Janeiro Group observations started in 1997, and therefore in 2008 one complete solar cycle time span can be analyzed. The series shares common principles of observation and analysis with the ones afore mentioned, and it is complementary on time to them. The distinctive features are the larger number of individual points and the improved precision. The series contains about 25,000 single observations, evenly distributed on a day-by-day basis. The typical error of a single observation is half an arc-second, enabling us to investigate variations at the expected level of tens of arc-second on a weekly basis. These features prompted to develop a new methodology for the investigation of the heliophysical scenarios leading to the observed variations, both on time and on heliolatitude. The algorithms rely on running averages and time shifts to derive the correlation and statistical incertitude for the comparison of the long term and major episodes variations of the solar diameter against activity markers. The results bring support to the correlation between the diameter variation and the solar activity, but evidentiating two different regimens for the long term trend and the major solar events.

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Solar diameter observations with the Astrolabe at Observatório Nacional - Rio de Janeiro

Cited by 14 publications

References 8 publications

Visual and CCD astrolabe observations of the solar radius

Visual and CCD astrolabe observations of the solar radius

Can AERONET data be used to accurately model the monochromatic beam and circumsolar irradiances under cloud-free conditions in desert environment?

A solar cycle lengthwise series of solar diameter measurements

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