October 6, 2016 - January 8, 2017
In 2006, the International Astronomical Union voted to reclassify Pluto as a dwarf planet. Demoting Pluto may have seemed drastic at the time, but it was not the first time astronomers have rethought what makes a planet a planet.
As scientists learn more about how the Universe works, they make discoveries that don't fit neatly into old ways of thinking. For ancient astronomers, any object that appeared to move relative to the stars was a planet. But that definition had to change once we realized it included very different objects like and asteroids and our Sun, but overlooked the most beloved planet of all: Earth!
The accepted definition of a planet has changed a lot in the past 500 years. In What is a Planet?, you'll explore artifacts from the Adler's collections that show how "planets" aren't what they used to be, witness how astronomers and the media reacted to Pluto's reclassification in 2006, and find out what makes a planet today.