Solar Radius Measurements at Mount Wilson Observatory

Lefebvre, S.; Bertello, L.; Ulrich, R. K.; Boyden, J. E.; Rozelot, Jean-Pierre

doi:10.1086/506134

Cited by 23 publications

(19 citation statements)

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“…We believe that there is here a key for understanding results obtained from ground-based measurements of the solar radius. We would also emphasize the role of the shallow photospheric layers (the leptocline; see Bedding et al (2007) and Lefebvre, Rozelot, and Kosovichev (2007)), which are the seat of many physical phenomena coupling the internal dynamics to the dynamics of the solar atmosphere. Further analysis of f -modes and space measurements are needed, but this study shows the great importance in observing solar eclipses.…”

Section: Discussionmentioning

confidence: 96%

“…If they are of solar origin, then, they will be caused by a magnification of the intensity at the limb owing to the magnetic field (Li et al, 2006). However, in the latter case, the solar variations of the diameter of 150 mas or more lead to limb radius variations irreconcilable with the results obtained from the f -mode observations (Lefebvre, Kosovichev, and Rozelot, 2007) and to incoherent astrophysical consequences (Rozelot, 2009). …”

Section: Introductionmentioning

confidence: 85%

“…Up to now, ground-based observations through astrolabes were only partially corrected for these effects (since they are also site dependent). Observations through other techniques (spectrography, transit drift time measurements, or heliometry) are more reliable; heliometer measurements at Pic du Midi Observatory (France) and spectrograph measurements at Mount Wilson (USA) are in good agreement (Lefebvre, Kosovichev, and Rozelot, 2007;Lefebvre, Nghiem, and Turck-Chièze, 2009). However, even if we include measurements from space (Kuhn et al, 2004;Gulbis et al, 2006), they suffer from the absence of an internally calibrated system, which would enable an unambiguous absolute determination of the solar radius.…”

Section: Introductionmentioning

confidence: 97%

“…Accurate measurements of the solar diameter at any heliographic latitude are very important for understanding the solar outer shape, that is, the free boundary of the gaseous envelope (Lefebvre et al, 2006). This shape must show deviations from a sphere, owing to the rotation of the fluid body under both the nonuniform mass and radial velocity distributions.…”

Section: Introductionmentioning

confidence: 99%

“…are time dependent. However, precise solar radius measurements are at the cutting edge of the techniques used: a difference of 20 mas (milliarcseconds) between the greatest solar radius (at the equator) and the lowest one (around 45 • -50 • of latitude) has been detected, and the mean radius does not change more than 15 mas, over time scales of eleven years or so (Kuhn et al, 2004;Lefebvre, Kosovichev, and Rozelot, 2007).…”

Section: Introductionmentioning

confidence: 99%

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Solar Radius Determination from Total Solar Eclipse Observations on 29 March 2006

et al. 2009

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Solar diameter measurements have been made nearly continuously through different techniques for more than three centuries. They were obtained mainly with ground-based instruments except for some recent estimates deduced from space observations. One of the main problems in such space data analysis is that, up to now, it has been difficult to obtain an absolute value owing to the absence of an internally calibrated system. Eclipse observations provide a unique opportunity to give an absolute angular scale to the measurements, leading to an absolute value of the solar diameter. However, the problem is complicated by the Moon limb, which presents asphericity because of the mountains. We present a determination of the solar diameter derived from the total solar eclipse observation in Turkey and Egypt on 29 March 2006. We found that the solar radius carried back to 1 AU was 959.22± 0.04 arcsec at the time of the observations. The inspection of the compiled 19 modern eclipses data, with solar activity, shows that the radius changes are nonhomologous, an ef-A. Kilcik ( ) 238 A. Kilcik et al. fect that may explain the discrepancies found in ground-based measurements and implies the role of the shallow subsurface layers (leptocline) of the Sun.

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Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 85%