Was Pluto the 8th planet from 1969 to 2009 and Neptune the 9th?

Except that isn’t the case at all.

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.

Does it bother you that atoms aren’t indivisible?

So we can call them isildurs?

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? :wink:

That’s not very damned funny.

Next time I will point out that Venus is actually a guy in a flying sailboat with a magic sapphire on his forehead.

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.

So the generic term for all three would be spaceballs?

OK, “rockballus”, “gasballus”, and “iceballus”. Happy now? :wink:

And a nitpick to Skald, in classical times there were seven planets, not five. The Sun and Moon were also included in that category.

And it’s a flying aluminum sailboat with a magic sapphire.

Quoth Biffy:

No, by analogy a “spaceball” would be a spherical object composed primarily of space, which would presumably refer to a black hole.

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.

Well blast your eyes. :smiley:

Here’s a video of Sagan to make up for things.

So are you in the Terra & Luna are a double-planet system crowd too?

That was fantastic. What a spectacular idea, to take that photograph, and what a speech to go with it!

I vote we name it Goofy. Who’s with me?

Yeah, I thought everyone knew about it. It’s what I was taught in elementary growing up.

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.