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Solar diameter with 2012 Venus Transit

Published online by Cambridge University Press:  27 June 2012

M. Faurobert ,
C. Fang ,
T. Corbard  and
C. Sigismondi
C. Sigismondi*
Affiliation:
Sapienza University of Rome and ICRA, Italy; University of Nice-Sophia Antipolis, France; IRSOL and GPA-Observatorio Nacional Rio de Janeiro, Brazil. e-mail: [email protected]
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Abstract

The role of Venus and Mercury transits is crucial to know the past history of the solar diameter. Through the W parameter, the logarithmic derivative of the radius with respect to the luminosity, the past values of the solar luminosity can be recovered. The black drop phenomenon affects the evaluation of the instants of internal and external contacts between the planetary disk and the solar limb. With these observed instants compared with the ephemerides the value of the solar diameter is recovered. The black drop and seeing effects are overcome with two fitting circles, to Venus and to the Sun, drawn in the undistorted part of the image. The corrections of ephemerides due to the atmospheric refraction will also be taken into account. The forthcoming transit of Venus will allow an accuracy on the diameter of the Sun better than 0.01 arcsec, with good images of the ingress and of the egress taken each second. Chinese solar observatories are in the optimal conditions to obtain valuable data for the measurement of the solar diameter with the Venus transit of 5/6 June 2012 with an unprecedented accuracy, and with absolute calibration given by the ephemerides.

Type
Research Article
Information
European Astronomical Society Publications Series , Volume 55: 4th French-Chinese Meeting on Solar Physics - Understanding Solar Activity: Advances and Challenges , 2012 , pp. 393 - 395
Copyright
© EAS, EDP Sciences 2012

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