The controversial decision by the International Astronomical Union to strip Pluto of its status as a major planet was a surprise to many, but seemed long overdue to others. The purpose of this page is to explain how Pluto was given status as a major planet, and why it may not have been worthy of that status.
The redefined Solar System. Major planets above, "dwarf planets" below. (IAU, apod060828)
The Search for Planet X
(original post now in The Discovery of Neptune and Uranus; more to follow as time permits)
Discovery photos of Pluto (Jan 23, left, and Jan 29, right, 1930). (Lowell Observatory Archives)
The arrows point to the position of Pluto in each image.
Alternating between the discovery images, as if in a blink comparator,
makes it easier to see the change in position of the previously unknown planet.