"did not accept the but evolved one of his own in which he makes the planets revolve about the Sun, but the Sun carries them with itself about the Earth. Part of his observations he reduced himself, publishing among other things a book on the , one on comets, and one on the lunar theory, and an important star catalogue. He had planned several other valuable works, but his early death cut short his projects. He was the first to perceive the importance of applying refraction to observations. He improved the values of the Sun's and Moon's , he discovered two variations in the Moon's longitude in addition to those already known, and one in latitude. In short he improved many values which depended on accurate observation for their determination."