Sentence:  I need not say that from Neptune the earth is completely invisible, as well as Mercury, Venus, and Jupiter. Saturn is a little star which departs from the sun up to 18°. For the <WSD>Neptunians</WSD> the solar system appears to be composed of the sun, Saturn, Uranus, their own world, and the planet which doubtless gravitates beyond Neptune. 
Meaning of the word marked with <WSD> tags:  An (imaginary) inhabitant of the planet Neptune.