 By this time , the apparent position of Ceres had changed ( mostly due to Earth 's orbital motion ) , and was too close to the Sun 's <unk> for other astronomers to confirm Piazzi 's observations . Toward the end of the year , Ceres should have been visible again , but after such a long time it was difficult to predict its exact position . To recover Ceres , Carl Friedrich <unk> , then 24 years old , developed an efficient method of orbit determination . In only a few weeks , he predicted the path of Ceres and sent his results to von Zach . On 31 December 1801 , von Zach and Heinrich W. M. <unk> found Ceres near the predicted position and thus recovered it . 
