This guest post comes from Trevor Owens, Special Curator for the Library of Congress Science Literacy Initiative.
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune: These are the eight planets of the solar system displayed on diagrams in our educational resources today. Of course, many of us still remember Pluto, which was considered a planet for many years until it was recently reclassified. Pluto’s demotion isn’t the only dramatic change that’s happened to educational solar system diagrams over the years, though.
Diagrams like these are models, and an important part of creating a model is defining what counts. Looking at diagrams of the solar system from different eras is a great way for students to think through how models represent our understanding of the solar system.
This 1846 diagram of the solar system, intended for use by students, presents plenty of opportunities to explore the changes in our idea of the solar system. Count the objects that look like planets, then compare them to a current diagram and compare the names. How many of these objects are you surprised to see, and are there any objects missing?
Four of the mystery objects, Vesta, Juno, Ceres, and Pallas are today considered asteroids. In the 1800s some of these would have been called planets, but astronomers kept discovering so many of them they made more stringent requirements for planet-hood.
Vulcan, the other oddity on the diagram, turned out to not exist at all. Based on the orbit of Mercury, astronomers thought there had to be another planet in-between it and the Sun.
You might have noticed that the names of most of these solar system objects have a common origin. Try to identify that origin, and speculate about why the objects have the names they do, instead of being named after their creators or other people or places.
What other changes do you notice between this diagram and the solar system as we know it today?