Pluto

Pluto was considered to be the ninth planet in the solar system from the time of its discovery by Clyde Tombaugh in 1930 until its reclassification as a dwarf planet in 2006.  There were good reasons for the reclassification, in spite of wide spread disagreement.  Regardless of what it is called, Pluto remains the largest known trans-Neptunian object (but not the most massive - that would be the dwarf planet Eris).

Pluto is not the first solar system object to have its status reassessed.  When Ceres was discovered in 1801 it was hailed as the eighth planet (Neptune was not discovered until 1846).  However, when many additional objects were discovered orbiting in the space between Mars and Jupiter, Ceres was demoted to a new class of objects called asteroids.  As part of the reclassification that demoted Pluto, Ceres was promoted to the rank of dwarf planet.

Pluto is currently located in the constellation of Sagittarius.  Its brightness of magnitude 14.5 requires a substantial telescope for visual observation.  I have photographed it many times, but don't recall ever seeing it through a telescope.  With objects that faint it can be a daunting challenge to pick them out from among the many similar background stars.

Here is an image of Pluto in its location on 5 Oct 2023:

E-P5 + Rokinon 135mm f2, ISO 1600, 60 s. 2-deg square.

Pluto is the faint dot in the exact center of the white circle.  Click on the image to gain access to the full-size version.

There is a road-side tribute to Clyde Tombaugh in the town of Burdett, KS, which we discovered during a cross-country trip this past summer:

 

Neptune, the farthest planet, is currently at magnitude 7.5 in the constellation Pisces.  It is 7824x more massive than Pluto, and 21.5x larger in diameter.  Triton, the largest moon of Neptune, has a diameter 1.2x larger than that of Pluto.  Neptune's apparent size is currently 2.5 arcsec, much smaller than a single pixel in the image below.

E-P5 + Rokinon 135mm f2, ISO 1600, 60 s. 2-deg square.