Cornelius Gemma or Cornelio Gemma (1535 1578) was a physician, astronomer and astrologer, and the oldest son of cartographer and instrument-maker Gemma Frisius. He was a professor of medicine at Louvain, and shared in his father's efforts to restore ancient Ptolemaic practice to astrology, drawing on the Tetrabiblos. As an astronomer, Gemma is significant for his observations of a lunar eclipse in 1569 and of the 1572 supernova appearing in Cassiopeia, which he recorded on November 9, two days before Tycho Brahe, calling it a "New Venus." With Brahe, he was one of the few astronomers to identify the Great Comet of 1577 as superlunary. Gemma is also credited with publishing the first scientific illustration of the aurora, in his 1575 book on the supernova