The definition of planet has changed much over the centuries; at first it simply meant “point of light in the night sky with a noticeable movement against the background of the seemingly fixed stars.” When that definition was current there were only 5: Mercury, Venus, Mars, Jupiter, & Saturn. (Earth was not considered a planet.) As our knowledge expanded we discovered about the nature of the solar system, including the fact that those bodies were all much nearer to Earth than the fixed stars, and qualitatively different from them, and that the first three bodies were more like one another (and Earth) than any of them were like the latter two. So the definition was changed to make the word planet something not quite so arbitrary. As we’ve learned more, the word as used by scientists has been adjusted.
Sure, if it maintains a spheroid shape due to gravitational attraction, has cleared its orbital neighborhood, and does not orbit another body (besides the Sun, of course). Why not?
The term 9th planet means 9th planet from the sun. If you were given interstellar directions and was told to go to the 9th planet from the sun during that time period that would mean Neptune.
There’s no proof it was a sapphire. You should have nitpicked THAT.
You’re right about the sun and moon being considered planets by the Greeks & Romans. And someone who isn’t me could make a good argument that Luna should still be considered a planet; I’ve emailed her with a request to join us.
Count me in the group that thinks they were right to declassify Pluto as a planet; I thought so as long as sophomore year astronomy. (By which I mean Brother What’s-his-name convinced me so.) But I also have a problem with calling the terrestrial planets the same sort of body as the gas giants.
Depending on how strictly you want to hang on the the “point” bit, the moon and the sun could also be considered to be planets (the moon was considered a planet in some Greek astronomical systems, AFAIK, though the sun might not have been). ETA: beaten by a mile by Chronos.
Chronos beat you to it. Hang your head in shame, as you also repeated my erroneous use of the word point in the definition. In the future we will expect better of you.
I’m one such person: You’ll note that I included Luna on my list of rockballs. It meets the criteria: It feels a stronger gravitational force from the Sun than from the Earth, it orbits (more or less) in the plane of the ecliptic (certainly closer to the ecliptic than to the Earth’s orbital plane), it’s big enough to maintain a spherical shape from gravity, it’s got a planet-like composition. It hasn’t cleared its orbit, but that’s a silly criterion anyway, since neither has Earth.
And good point about the sapphire. Some of the Elven-gems are explicitly said to have been made from mithril, but the Silmarils weren’t specified.
It’s not like the teachers ever taught something wrong by over simplifying it is it. This is why I asked the question. I thought there might be people, besides the author that considered Pluto would be the 8th planet during the stated period. I was interested in what was the point of view when the book was published.
