Question on the history of calculating the orbital of planets

  1. I learnt on the textbook that human calculated the orbital of planets that near the Earth first then based on the difference of the actual data of the planet orbitaland that of human predicted, human calculated out other planets' orbital and predicted some planets like Neptune and Pluto. I think, however, shouldn't the actual data be already affected by planets that had not been found? Thus I think the first-hand data is not very precise. Could someone solve my confusion? Thx
     
  2. jcsd
  3. Drakkith

    Staff: Mentor

    The only planet that was predicted to exist before it was discovered was Neptune. The orbit of Uranus was calculated and after a time it was discovered that small errors were present. These errors could be explained by another planet further out exerting it's gravitation on Uranus. Calculations were done and the planet was subsequently found about 1 degree from its predicted location in the sky.

    I don't count Pluto because its discovery was a complete fluke. The orbit of Uranus was thought to be influenced by yet another planet further out, but it turned out that the mass of Neptune had simply been incorrect.

    And you are correct in that the our measurements and calculations are much more accurate now than they were in the 1800's and early 1900's. This is due to longer periods of time to measure the planets motions combined with a vastly higher quality of optics and the development of digital sensors.
     
  4. Thank you very much! It helps me a lot.
     
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