07 February 1979 : On this day, Pluto enters Neptune’s orbit for the first time since the planets’ discovery.
Most planets’ orbits are essentially circular, whereas Pluto’s is more elliptical in shape. Pluto’s orbit is more eccentric than that of the other planets.
A circle’s eccentricity is equal to zero. However, Pluto’s eccentricity is 0.251, implying that its orbit crosses that of Neptune from February 7, 1979 to February 11, 1999, bringing that planet closer to the Sun.
Pluto was thought to be the ninth planet from the Sun when Clyde Tombaugh discovered it in 1930.
Pluto temporarily entered Neptune’s orbit on February 7, 1979, making it the eighth planet from the Sun.
Following the discovery of numerous objects of comparable size in the Kuiper belt, Pluto’s classification as a planet was called into question after 1992, and Pluto was excluded and reclassified as a dwarf planet.
On August 24, 2006, the International Astronomical Union General Assembly designated Pluto as a “Dwarf Planet” (IAU).
