One of the most advanced astronomical works of its day, the Astronomicum Caesareum quickly became outdated. Its calculations and charts, although reasonably accurate, were based on the Ptolemaic system in which the sun revolves around the earth. Less than three years later, in 1543, Copernicus would publish his landmark De Revolutionibus Orbium Coelestium, defining the modern heliocentric model with the sun at the center of the solar system.
According to some estimates, approximately 120 copies of the Astronomicum Caesareum survive, probably the majority of the print run. The astronomer Tycho Brahe recorded that he paid twenty florins for his copy (roughly equivalent to $3,000 today).
High-resolution images from the Bodleian Library's copy of the Astronomicum Caesarium are available online at the Rare Book Room. A full pdf copy can be downloaded from the Digital Rare Book Collection of the Vienna University Observatory.
Owen Gingerich. Petrus Apianus, Astronomicum Caesareum.
S.A. Ionides. "Caesars' Astronomy (Astronomicum Caesareum)." Osiris vol. 1 (Jan. 1936), pp. 356-389. Contains a detailed analysis of the text and astronomical calculations.