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How many planets are in our solar system? Is it eight… or nine?

For a long time, children around the world were taught that our solar system had nine planets, including a small, distant one named Pluto. But in 2006, Pluto was reclassified. It was no longer considered a “real” planet, and the official number of planets dropped to just eight.

Why did this happen? Why was Pluto removed from the list of planets? And what exactly is a planet anyway?

In today’s episode of Thinking in English, we’ll look at what a planet actually is, why Pluto used to be a planet but isn’t anymore, and how science changes over time. We’ll also talk about the history of planet discoveries, like Neptune and Uranus, and how our understanding of the solar system has developed.

This episode is also a great chance to learn scientific vocabulary and practice thinking critically in English. We’ll explain important terms like orbit, gravity, dwarf planet, and clearing its orbit. And we’ll discuss some fascinating facts about space, science, and the nature of definitions themselves.

So… is Pluto really a planet? Or not? Let’s find out.

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TRANSCRIPT - https://thinkinginenglish.blog/2025/05/26/339-pluto-what-is-a-planet-english-vocabulary-lesson/

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EMJ December 2019