Heinrich d'Arrest, a student at the Berlin Observatory, suggested the following. A newly drawn map of the sky in the region of Le Verrier's predicted area could be compared with the current sky. It was needed to look for the change of position of a planet, compared to a fixed star. Neptune was then discovered that very night on 23 September 1846, within 1° (one degree (angle)) of where Le Verrier had predicted it to be, and about 10° from Adams' prediction. Challis later found out that he had seen the planet twice in August, failing to recognize it due to his careless work approach.