Johannes Stadius

Johannes Stadius or Estadius (Dutch: Jan Van Ostaeyen; French: Jean Stade) (ca.

[citation needed] After receiving his education at the Latin school of Brecht, Stadius studied mathematics, geography, and history at the Old University of Leuven, where one of his teachers was Gemma Frisius.

An ephemeris (plural: ephemerides) (from the Greek word ephemeros, "daily") was, traditionally, a table providing the positions (given in a Cartesian coordinate system, or in right ascension and declination or, for astrologers, in longitude along the zodiacal ecliptic), of the Sun, the Moon, and the planets in the sky at a given moment in time; the astrological positions are usually given for either noon or midnight depending on the particular ephemeris that is used.

Frisius had in a letter written in 1555 urged Stadius not to be afraid of being accused of believing in a moving earth and a stationary sun (i.e. the theory of Copernicus) or of abandoning the medieval Alfonsine Tables in favor of his own observations.

In this letter Frisius further wrote that the system devised by Copernicus gave a better understanding of planetary distances, as well as of certain features of retrograde motion.