Astronomical books often contained an illustrated frontispiece especially designed for
the title in the 17th Century. The fact that several frontispieces were commissioned from distinguished artists,
and that the complicated pictorial program could be explained in an extensive introduction, indicate the importance
of this kind of illustration. This paper aims at investigating how the astronomer wanted to present himself and
his work, how issues of status and credibility were handled, and how a patron, other important persons or organizations
were acknowledged or refuted.