Kiril Popoff - a pioneer of Bulgarian Astronomy. Annual of Sofia University St. Kliment Ohridski. Faculty of Mathematics and Informatics, [S. l.], v. 98, p. 25–32, 2008. Disponível em: https://annual.uni-sofia.bg/index.php/fmi/article/view/126. Acesso em: 4 feb. 2026.