In this talk we revisit from the perspective of science diplomacy the British astronomical expeditions which observed the 1919 total solar eclipse and tested Einstein’s prediction of light bending. It has been already analyzed in the literature how Eddington and British astronomers voiced arguments in favor or against the maintenance of relations between British and German scientists during the Great War. While the former case may be classified as informal science for diplomacy, we address in this talk another instance of informal science diplomacy, falling under the heading diplomacy for science. We refer to the actions practiced by expeditioners and/or communities of local/national astronomers in Brazil, associated with astronomical observations carried out by Charles R. Davidson and Andrew C.C. Crommelin in Sobral, the second city of the state of Ceará. We analyze the complex process of mediation involving not only formal channels of Brazilian diplomacy but also informal diplomatic relations between British and Brazilian astronomers (and even an American astronomer operating in Argentina) which prepared the ground for the astronomical observations. We detail how, orchestrated by Henrique Morize, director of the National Observatory of Rio de Janeiro, under the authoritative role of Charles Dillon Perrine, director of the National Observatory of Argentina, in Córdoba, collaboration between scientific experts of different nationalities was achieved. We also address the various dimensions of the mediation process’ outcome (political, diplomatic, scientific, etc.), focusing on its profound impact on the promotion of the Brazilian scientific community abroad and the affirmation of astronomy in Brazil.