Thinking in English 339. Pluto: What is a Planet? (English Vocabulary Lesson)
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May 26, 2025 Delve into the intriguing debate surrounding Pluto's status as a planet. Explore the reclassification that occurred in 2006 and what defines a planet. Discover the history of planet discoveries, including Neptune and Uranus, and the criteria set by the International Astronomical Union. Learn important scientific vocabulary like orbit and dwarf planet, while grappling with public sentiment and new findings from the New Horizons mission. Is Pluto really a planet? Join the discussion and expand your understanding of our solar system!
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Pluto's Planet Status Changed
- Pluto was considered the ninth planet until 2006 when it was reclassified and removed from the planet list.
- This change lowered the official number of planets in our solar system to eight.
Neptune's Discovery By Prediction
- Neptune was discovered through predictions based on Uranus's movements, before it was ever seen.
- French astronomer Urban Leverrier calculated Neptune's location by math alone, leading to its discovery.
Planet Definition by IAU
- The IAU defined a planet by three criteria: orbit the Sun, be spherical in shape, and clear its orbit.
- Pluto fails the third test as it shares its orbit with other objects, so it's classed as a dwarf planet.