The variation of the solar diameter and irradiance : eclipse observation of July, 11, 2010

TL;DR

This paper discusses measurements of the solar diameter and irradiance variations using eclipse observations, highlighting new experimental approaches and the importance of precise lunar profiles for future accuracy.

Contribution

It introduces new eclipse-based measurement techniques and a refined definition of the solar edge, advancing the understanding of solar diameter variability.

Findings

Preliminary eclipse measurements of solar diameter using CNES photometer.

Development of a new solar edge definition less affected by scattered light.

Emphasis on lunar altimetry data for improved future solar diameter measurements.

Abstract

The variation of the solar diameter is the subject of hot debates due to the possible effect on Earth climate and also due to different interpretations of long period solar variabilities, including the total solar irradiance. We shortly review the topic and show that rather long term variations, corresponding to a length well over a a solar magnetic cycle, are interesting to consider. The very recently launched mission "Picard" is entirely devoted to the topic but will just permit a short term evaluation. At the time of the last total solar eclipse of 11/07/2010, several experiments were prepared to precisely measure the transit time of the Moon related to the precise value of the solar diameter. Preliminary results coming from the use of a specially designed CNES photometer, put on different atolls of the French Polynesia, are presented. In addition the results of new experiments devoted to fast observations of flash spectra, including their precise chronodating, are illustrated and discussed. A new definition of the edge of the Sun, free of spurious scattered light effects strongly affecting all out of eclipse observations, is emerging from these observations, in agreement with the most advanced attempts of modelling the outer layers of the photosphere. We also argue for a definite answer concerning the solar diameter measurement from eclipses based on a better precision of lunar profiles coming from lunar altimetry space experiments which will be possible in the following decades.