How many planets have ever completed an orbit around the sun: 8, since Pluto has such a long orbital period that in it’s entire time as a planet it did not even finish a single one.
Comment on Pluto is still a planet, just a dwarf one
diverging@piefed.social 3 weeks ago
How many planets are in orbit around the sun? 8
How many planets are in the entire universe? 8, because a planet has to orbit the sun.
DivineDev@piefed.social 3 weeks ago
- diverging@piefed.social 3 weeks ago
Pluto has completed millions of orbits around the sun.
At the time of the IAUs release of the definition of a planet, Neptune had not completed an orbit since its discovery, and yet they still called it a planet. Clearly, this weird and arbitrary statement that you have put forth did not matter.
teslekova@sh.itjust.works 3 weeks ago
Neptune has completed one though. So Pluto is the only planet to officially not complete an orbit while it was called a planet. It doesn’t affect whether it’s a planet or not, it’s just an interesting quiz question.
DivineDev@piefed.social 3 weeks ago
I think it was sufficiently clear to just be a fun fact, not the implication that pluto did not complete orbits around the sun before it was discovered or whatever
That’s just for our own solar system.
The draft proposal for the definition of a planet was debated vigorously by astronomers at the 2006 IAU General Assembly, and a new version slowly took shape. This new version was more acceptable to the majority and was presented to the members of the IAU for a vote at the Closing Ceremony of the General Assembly. By the end of the Prague General Assembly, IAU members voted that the definition of a planet in the Solar System would be as follows: "A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit. (p. 1)" More generally, a planet: a) orbits its host star, just as the Earth and Jupiter orbit the Sun, b) is large enough to be mostly round, and c) must have an important influence on the orbital stability of the other objects in its neighbourhood.
https://www.iau.org/IAU/Science/What-we-do/Pluto-and-the-Developing-Landscape-of-Our-Solar-System.aspx
The IAU resolution (pdf) that they voted on does not include what comes after “More generally”. The page that you link to is apparently the source and is not official.
That PDF says “Definition of a Planet in the Solar System” and “The IAU therefore resolves that planets and other bodies in our Solar System be defined into three distinct categories in the following way”.
I mean, what would you call the big, roughly ball-shaped thingies orbiting Kepler-62?
Because planets only exist in the solar system.
They attempted to create a definition for an “exoplanet” but that never passed, so aggregations of matter orbiting stars outside the solar system have no official name.