Free Astronomy Magazine January-February 2020

14 JANUARY-FEBRUARY 2020 HISTORY tion was to compute a tempo- rary orbit. To contribute to this complex operation, Tombaugh quickly reviewed the plates taken both over the last year and in which the planet might have been present. That day, Lampland failed to calculate a satisfactory orbit, but foresaw the exact location where the planet would be found on the night between 19 and 20 Feb- ruary. At 11 P.M. on the 19 th , defying bad weather condi- tions, Tombaugh began to ex- pose a new plate. After developing and putting it in the blink, he saw the planet exactly in the expected posi- tion. Lampland suggested mak- ing a contact copy on film of the planet-centered star field to have a manageable map for a direct visual comparison. On the evening of the 20 th , the weather conditions were favor- able, and Lampland and Tombaugh, to- gether with Vasto Slipher, aimed the 24-inch refractor, symbol of the observa- tory, towards the new planet. Theirs were the first eyes to knowingly observe Planet X. The understandable initial emotion soon turned into disappointment when the team realized that not even at the highest mag- nifications of that powerful refractor was it possible to distinguish even a hint of a planetary disc. The appearance remained stellar, meaning that the planet was not faint due to a very low albedo, as initially supposed, but because it was very small. Ac- cordingly, its mass was not sufficient to ex- plain the residual perturbations observed in Uranus’ motion. The newly discovered plan- et could not therefore be the one forecast C lyde Tombaugh in the 1950s, when he worked at the White Sands Missile Range in New Mexico. [Bettmann/Getty] On the left, the demonstration of how our vision of Pluto has changed from discovery to today.