 This notation was also used to indicate an observation error so it was not until the original records of the observatory were reviewed that it was established with certainty that the object was Neptune and the position error in the observations made two nights apart was due to the planet's motion across the sky.The discovery of these records of Neptune's position in 1795 led to a better calculation of the planet's orbit.John Herschel almost discovered Neptune the same way his father, William Herschel, had discovered Uranus in 1781, by chance observation.