"The Orbiting Object Formerly Known As Pluto!"
The name is still Pluto - it's just not considered a planet. I think they recategorized it as a "dwarf planet" or something odd like that.
It's because they found a new object larger than Pluto that would classify as a planet.
And for some strange reason which I cannot phantom, they don't want any more new planets in our solar system.
Seriously, what happened to the coolness of discovering new planets? Now it seems something to be avoided

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Anyways, back on topic:
Yeah, most games have to deal with scale at some point or another. A realistic scale usually just isn't any fun.
I remember playing Transport Tycoon, and you had to deal with ships vs road vehicles vs aircraft - if it were completely realistic, the differences in speed would make the game practically unplayable. Think about it: The distance an aircraft can cover in mere hours takes a road vehicle days or a ship weeks. The speeds were therefore fudged - enough, in fact, that a fast but subsonic train was actually faster than a supersonic aircraft, lol.
When talking about a space based game in Galactic Civilizations, we're talking vast differences in scale. Not just the size of the various objects, but the distance between them as well.Distances in our galaxy are vast.
So, yeah, it's a tradeoff of realism vs playability. Make the scale too realistic, and it's just not going to be fun anymore.
And an off-topic note about image quality - what in the world happened to those pics? It looks like somebody converted the file between several different lossy file formats before they finally saved it

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That's not Draginol's fault, though - looks like they were that way to begin with. I couldn't find the original images.