They would likely have no clue. First of all, the world didn't know about Neptune, Uranus, or Pluto. They were discovered in the 18th through 20th centuries. To them, the only planets that existed were Mercury, Venus, Mars, Saturn and Jupiter. And only the educated would know that much. Planets were thought to be wandering stars, and differing only in that respect from stars. So why would there be these few objects singled out from all of the lights in the heavens? And why would they be dark? What would the different colors mean? They didn't know Saturn had rings, so that would puzzle them. They believed that the Earth was the center of the universe so the drawing of the sun as the center of the solar system would puzzle them, too. The earth wouldn't have been in the same category as the 5 known planets, either, so it being put side by side with them would also be odd. The earth wasn't a planet, it was earth, to them. And they didn't know about moons. The earth had a moon, but the moons of other planets wouldn't have been known, so that would have been puzzling as well.