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Timeline · 4 events

Planet & Dwarf-Planet Discoveries

When the outer worlds of the Solar System were found.

  1. 1781

    Uranus discovered

    Found by William Herschel — the first planet discovered with a telescope.

  2. 1846

    Neptune discovered

    The first planet found through mathematical prediction.

  3. 1930

    Pluto discovered

    Found by Clyde Tombaugh; long counted as the ninth planet.

  4. 2006

    Pluto reclassified as a dwarf planet

    Following the IAU's formal definition of 'planet'.

Sources & references

The primary and reference sources this topic draws on.

  • NASANational Aeronautics and Space Administration

    Mission data, planetary science, space telescopes, and public-domain imagery.

    Most NASA-produced imagery is in the public domain; individual items are checked for usage terms before publication.

  • IAUInternational Astronomical Union

    Official naming, definitions, constellation boundaries, and astronomical nomenclature.