(Every day until December 25, I’m posting a science-related image or video and description.)
An orrery is a mechanical way to visualize the positions of the planets in their orbit around the Sun. The most marvelous orreries are works of art in brass, geared so that a turn of a crank or other motive force provides a relatively accurate model of the length of time for each planet to complete its year. (Some of my school classrooms had orreries, but they were flimsy constructions of wire.) Some of the more complex models include Earth’s Moon, and maybe some of the other Solar System moons as well.
The video above is a kind of orrery, too, but for the exoplanets found by the Kepler mission. (I recommend making the video full-screen, since it has an incredible number of planets in it! I can’t find an exact number published anywhere, even on the video’s YouTube page, so I’ll update if I find that information out.) University of Chicago astronomer Daniel Fabrycky used observational data to reconstruct the relative sizes and periods of orbit for all the exoplanet candidate systems. The rocky (terrestrial) worlds are represented in gray, but you’ll have to squint to see them — they’re much smaller than the dramatic super-Jupiter planets. The other colors are a representation of how close each world is to its host star.
Note that the host stars themselves are not represented, nor is the size of the planet on the same scale with its orbit, since that’s not really possible to do. (Orbits are much larger than planets, so to represent both accurately requires a lot of space.) However, this orrery has a lot of information about exoplanet sizes and orbits — almost too much. As we continue to discover other planets orbiting other suns, it will not be practical to make a single orrery with all of them represented. But that’s fine by me: a visualization like this helps us realize how much we’ve learned about exoplanets in the last 15 years. If we are spoiled by wonder and overwhelmed by knowledge, it’s good to stop and reflect on how fortunate we are — and rededicate ourselves to learning still more.