Solar Diameter Monitor: an instrument to measure long-term changes

Brown, Timothy M.; Elmore, D.; Lacey, L.; Hull, Howard K.

doi:10.1364/ao.21.003588

Cited by 22 publications

(11 citation statements)

References 10 publications

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“…In our view, this contrast could reflect the difference between the bahaviour of a very simple and quite compact metrological system like that of the Danjon astrolabe as can be seen in Fig. 1 (see also Danjon 1960;Noël 2003) and a far more complicate and less compact instrument such as the Solar Diameter Monitor (see Brown et al 1982).…”

Section: Other Results Of Solar Radius Measurementsmentioning

confidence: 97%

“…An eventual drift of the focal distance during this short lapse can be accurately controlled. This is a prime advantage, since long-term stability of the instrumental system is the most stringent requirement of other methods for measuring the solar diameter (Brown et al 1982). Since astrolabe observations are made at a constant altitude, the results are free of differential refraction, and according to the reduction method, eventual spurious effects in atmospheric refraction are cancelled (Noël 2003).…”

Section: Solar Radius Measurements With a Modified Danjon Astrolabementioning

confidence: 99%

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Solar cycle dependence of the apparent radius of the Sun

Noel

2003

A&A

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Abstract. Visual astrometric observations of the Sun covering the second and first part of solar cycles 22 and 23 respectively, have been carried out during the last 13 years with the Danjon astrolabe of Santiago, Chile. These observations give, among other solar parameters, an absolute value of the Sun's apparent radius. We report here the results obtained from 4092 homogeneous radius measurements at 30• and 60• zenith distances. The data set shows at both zenith distances a significant radius variation in phase with magnetic activity. Moreover, the observations at 30• , which are less affected by atmospheric noise, give a significantly higher correlation coefficient between radius variation and sunspot numbers. Other investigations of solar radius variations during the last decades based on different observing techniques, as well as two analyses of historical data, are commented. Most of them show also positive correlations between radius variation and solar activity. With the noted exception of Calern, France, the results obtained at other astrolabe stations during recent years are in agreement with Santiago. The discrepancy between Calern and Santiago and its probable cause are discussed.

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Section: Other Results Of Solar Radius Measurementsmentioning

confidence: 97%

Section: Solar Radius Measurements With a Modified Danjon Astrolabementioning

confidence: 99%

Solar cycle dependence of the apparent radius of the Sun

Noel

2003

A&A

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“…Moreover, variations have not always been noted from the observation series of the solar programs. Using the observations recorded with the solar diameter monitor (Brown et al 1982) during the period 1982 to 1987, Brown & Christensen-Dalsgaard (1998) did not observe any variations. In their work, they used special methods in order to eliminate some atmospheric effects.…”

Section: Introductionmentioning

confidence: 93%

Error due to atmospheric turbulence effects on solar diameter measurements performed with an astrolabe

Lakhal¹,

Irbah²,

Bouzaria³

et al. 1999

Astron. Astrophys. Suppl. Ser.

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Abstract. Diameter measurements performed with the solar astrolabe are affected by instrumental and atmospheric effects. The problem is to know how these effects contribute to the error on diameter measurements. Thus, a numerical simulation is developed to bring some responses to this problem. For this purpose, synthetic images of the Sun similar to the ones obtained by the instrument through the Earth atmosphere are simulated. A fractal model is used to generate randomly perturbed wavefronts and therefore optical response of the whole system, atmosphere and instrument. Many sequences of solar images are then simulated for various observation conditions (Fried's parameter r 0 , spatial coherence outer scale L 0 and atmospheric characteristic times). They are used to define the time of contact of the direct and reflected solar images which is fundamental in the solar astrolabe experiment. It is then studied as a function of the observation conditions relatively to the experimental characteristics (exposure time).

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“…The advantage of the FFTD method is that it is not sensitive to small amplitude variations of the center-to-limb darkening function slope (Hill, Stebbins, and Oleson, 1975;Brown, 1982;Stebbins and Wilson, 1983). Brown and Christensen-Dalsgaard (1998) have shown this advantage for the solar diameter measurement made with the SDM (Solar Diameter Monitor) instrument. This method consists in calculating the variation of solar radius as a function of the parameter a and then representing this variation by a linear fit.…”

Section: Fftd Property To Correct Small Slope Variations Of the Solarmentioning

confidence: 99%

Processing Method Effects on Solar Diameter Measurements: Use of Data Gathered by the Solar Disk Sextant

Djafer¹,

Thuillier²,

Sofia

et al. 2008

Sol Phys

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To determine the apparent diameter of the Sun, it is first necessary to measure the shape of the intensity profile of the solar limb with an imaging optical system (hereafter denoted as a solar-limb profile). The inflection point of the limb profile is usually used as a reference for calculating the diameter. Because this point may be difficult to determine in the presence of noise, it is necessary to define an appropriate filtering process that eliminates noise while preserving the position of the inflection point. In this paper we study two filtering techniques, one based on the compact wavelet transform and the other on the finite Fourier transform definition, that meet these requirements. The application of these two techniques to data gathered by the Solar Disk Sextant experiment shows that the solar radius increased from 1992 to 1996 by about 197 mas. However, a previous analysis of the same data and our present analysis provide a difference in the measured radii of about 92 mas. We show that this difference is entirely traced to the filtering process

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Solar Diameter Monitor: an instrument to measure long-term changes

Cited by 22 publications

References 10 publications

Solar cycle dependence of the apparent radius of the Sun

Solar cycle dependence of the apparent radius of the Sun

Error due to atmospheric turbulence effects on solar diameter measurements performed with an astrolabe

Processing Method Effects on Solar Diameter Measurements: Use of Data Gathered by the Solar Disk Sextant

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