Solar radius change between 1925 and 1979

Abstract

By analysing numerous reports, from different locations, on the duration of totality of the solar eclipses on 24 January 1925, and on 26 February 1979, we have found that the solar radius at the earlier date was 0.5 arc s, or 375 km larger than at the later date. The correction to the standard solar radius found for each eclipse was different when different subsets of the observations were used (for example, edge of path of totality timings compared with central timings), suggesting the existence of systematic inaccuracies in our knowledge of the lunar figure. However, the differences between the corrections for both eclipses were very similar for all subsets considered, indicating that changes of the solar size may be reliably inferred despite the existence of the lunar figure errors, as long as the proper consideration is made of the distribution of the observations. We consider that these results are strong evidence in support of the occurrence of solar radius changes on shorter than evolutionary time scales.