2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/11062This question, which often comes in when discussing solar neutrinos, is not clearly analysed in any textbook, to our knowledge. In this note we give a simple estimate of the flow time, also reminding its (ir)relevance to the solar neutrino problem.3 pages, RevTeX, plus 1 postscripts figureAstrophysicstext