Tomorrow (23rd) marks the 176th anniversary of the discovery of Neptune (~ 1.07 years on Neptune; 164.8 Earth years).
Johann Gottfried Galle an astronomer at the Berlin observatory found Neptune at the behest of Urbain Le Verrier who calculated its position by hypothesizing that some body must perturb Uranus orbit to explain the distinct deviation from the predicted motion by Newton's law of universal gravitation.
Le Verrier couldn't find a single French astronomer willing to take a look out at the sky after presenting his extensive calculations to the French Academy on 31 August. On 18 September he then wrote a letter to the German astronomer Galle at the Berlin observatory.
After receiving the letter 5 days later Galle immediately set up his telescope the same night and found a +8 mag star (within 1 degree of the Le Verrier's calculation) not listed on the official Prussian star chart. The next night he managed to measure the star itself moving by 4 arcseconds, finally confirming Le Verrier prediction of a new planet (and to this day last).
At ~30 AU (30x the distance sun-earth; Uranus being at ~20 AU) the discovery instantaneously made the solar system 1.5x bigger ;)