An early defender of the ideas of Copernicus, Kepler and Galileo, Ismael Bullialdus has been called "the most noted astronomer of his generation".

His older brother was originally named after their father Ismael, but died shortly after birth.

Enjoying the patronage of the de Thou family, Bullialdus worked for 30 years in Paris as a librarian associated with the brothers Jacques and Pierre Dupuy, who were working on the Bibliothèque du Roi (Bibliothe), France's first royal library.

Bullialdus was an active member of the Republic of Letters, the long-distance intellectual correspondence network that had emerged as an international community of self-proclaimed scholars and literary figures.

Arguably most notable were the ten volumes of original autographs addressed to Nicolas-Claude Fabri de Peiresc.

[4] The book widened the awareness of Kepler's planetary ellipses, however, whereas Kepler used a physical cause to explain planetary motion, and called on math and science to support his theory, Bullialdus offered an entirely new cosmology, the "Conical Hypothesis".