Today marks 16 years when pluto stopped being a planet

August 24, 2006, is indeed a significant date in the history of astronomy. On this day, the International Astronomical Union (IAU) redefined the term "planet" and reclassified Pluto as a dwarf planet.

Prior to 2006, Pluto was considered to be the ninth planet in our solar system, but it was always a bit of an oddball. It was much smaller than the other planets, and its orbit overlapped with that of other objects in the Kuiper Belt, a region of icy bodies beyond Neptune.

The reclassification of Pluto was sparked by the discovery of several other objects in the Kuiper Belt that were similar in size and composition to Pluto. One of these objects, known as Eris, was found to be slightly larger than Pluto, which raised questions about the criteria for what constitutes a planet.

The IAU formed a committee to study the issue and develop a new definition of a planet. After much debate and discussion, the committee proposed a definition that would define a planet as an object that:

1. Is in orbit around the Sun.
2. Has sufficient mass to assume a hydrostatic equilibrium shape (i.e., it is nearly round in shape).
3. Has cleared the neighborhood around its orbit.

The third criterion, that a planet must have cleared the neighborhood around its orbit, was the key factor in the reclassification of Pluto. Pluto's orbit overlaps with that of other objects in the Kuiper Belt, and it is not a dominant gravitational force in its orbit. Therefore, it was determined that Pluto had not cleared the neighborhood around its orbit and did not meet the new definition of a planet.

Instead, Pluto was classified as a dwarf planet, a new category of objects that was created by the IAU. Other dwarf planets in our solar system include Eris, Ceres, Haumea, and Makemake.

While the reclassification of Pluto was a significant change, it has also led to a greater understanding and appreciation of the diversity of objects in our solar system. Pluto may no longer be considered a "full-fledged" planet, but it remains an important and fascinating member of our celestial neighborhood.