A scion of the Castilian nobility, Juan de Rojas moved to Flanders with the court of Emperor Charles V (1500-1558) and studied with Reiner Gemma Frisius (1508-1555) in Louvain. He became famous in Europe mainly thanks to the dissemination of a new type of astrolabe that he developed using an orthographic projection of the celestial sphere. The instrument was unveiled in Commentariorum in astrolabium, a widely circulated treatise published in Paris in 1551.