Old as the stars.
When I was in third grade, we had to memorize the planets by distance from the sun. The list was: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Sometimes, Pluto and Neptune were reversed, and it was always noted that the asteroid belt was between Mars and Jupiter. We would talk about the days of Galileo, when they thought moons of Jupiter (and later Saturn) were planets, as if the world were ruled by foolish superstition.
Today, that list would go: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Or, if you counted the dwarf planets: Mercury, Venus, Earth, Mars, Ceres (in the asteroid belt,) Jupiter, Saturn, Uranus, Neptune, Pluto and Eris. There are currently over 70 more candidates for classification as dwarf planet in the solar system, a few inside the asteroid belt, but most within the Kuiper belt. When I was a kid, we didn't even know there was a Kuiper belt. It's 20 times the width of the asteroid belt and about 100 times as massive, and we didn't even know it was there until I was 12.
Science was totally cool until it started making me feel old.
Today, that list would go: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Or, if you counted the dwarf planets: Mercury, Venus, Earth, Mars, Ceres (in the asteroid belt,) Jupiter, Saturn, Uranus, Neptune, Pluto and Eris. There are currently over 70 more candidates for classification as dwarf planet in the solar system, a few inside the asteroid belt, but most within the Kuiper belt. When I was a kid, we didn't even know there was a Kuiper belt. It's 20 times the width of the asteroid belt and about 100 times as massive, and we didn't even know it was there until I was 12.
Science was totally cool until it started making me feel old.