Pluto Demoted Day - After nearly 80 years as an official planet, Pluto was demoted down to a dwarf planet.

Pluto Demoted Day 2024 – August 24, 2024

National Pluto Demoted Day is on August 24 and we are busting out our telescopes to get in the spirit of planetary study! Can you believe that after nearly 80 years as an official planet, Pluto was demoted down to a dwarf planet? In 2006 the International Astronomical Union (IAU) determined that since Pluto is not the dominant object in its orbit around the sun, it could no longer be an official planet. Other large bodies — like Pluto’s own moon, are found in its region.

History of Pluto Demoted Day

Pluto was discovered in 1930 by astronomer Clyde Tombaugh, making it the ninth planet in our solar system. It’s a relatively cold planet that exists outside the orbit of Neptune. After its discovery, Lowell Observatory had over 1,000 suggestions for what to name the newly found planet. The eventual winner was Pluto, named after the Roman god of the underworld. In 1992, questions arose around Pluto’s legitimacy as a planet after the discovery of large objects in its region, including one that actually had a larger mass than Pluto itself. Eventually, in 2006, the International Astronomical Union (IAU) settled on a definition for ‘planet,’ which ultimately excluded Pluto. From that point forward, it has been known as a ‘dwarf planet.’ A dwarf planet is defined as is a celestial body that orbits the sun and has enough mass to assume a nearly round shape but that has not cleared the area around its orbit and is not a moon.

Pluto Demoted Day timeline

First Discovered

Pluto is first discovered by Clyde Tombaugh and is determined to be the ninth planet in the solar system.

Pluto’s Largest Moon

Charon — the largest of Pluto’s five moons, is discovered by the United States Naval Observatory.

Other Large Bodies

In 2005, Eris, another dwarf planet larger in mass than Pluto, is discovered in the Kuiper belt (a region of icy objects outside Neptune’s orbit, which includes Pluto).

The Demotion

The International Astronomical Union (IAU) officially downgrades Pluto from a full-size planet.

Pluto Demoted Day FAQs

How many moons does Pluto have? 

Interestingly, Pluto has five moons in its orbit. They are named Charon, Styx, Nix, Kerberos, and Hydra. 

Has a spacecraft ever made it to Pluto? 

Yes! In 2015 the New Horizons spacecraft completed a flyby of Pluto and recorded important information and readings about the planet and its moons.  

How big is Pluto?

Pluto is significantly smaller than planet Earth. With a diameter of 1,473 miles, it’s less than one-fifth the size of the Earth. 

How to celebrate Pluto Demoted Day

  1. Try some papier mâché!

    We all remember making volcanoes out of papier mâché as kids and trying not to make too much of a mess. What better way to celebrate Pluto than to bust out some flour, water, and old strips of newspaper and make the solar system! It’s a great way to entertain kids while at the same time providing some planetary education.

  2. Watch a space documentary

    Documentaries about murders or celebrities tend to get a lot of press, but there are countless interesting ones about planets and the solar system. There is quite literally an entire universe outside your window to discover. Take this day as an excuse to plop down on the couch and learn more about Pluto and all the planets.

  3. Try stargazing

    Most of us can’t afford a powerful telescope like the ones at fancy observatories, but that doesn’t mean we can’t try out stargazing. It’s even possible to see Pluto! You’ll need a decent telescope and a detailed star atlas to help guide your search.

5 Facts About Pluto That Will Blow Your Mind

  1. A day on Pluto is equivalent to six Earth days

    Due to its distance from the Sun, a day on Pluto lasts 153 hours.

  2. Where the name came from

    A youngster by the name of Venetia Burney (only 11 years old) came up with the name Pluto in 1930.

  3. Bring a winter jacket

    The surface of Pluto is super cold, with a temperature ranging from -378°F to -396°F.

  4. A long way from the Sun

    Pluto sits 3.6 billion miles away from the Sun.

  5. Planet X

    Prior to its official discovery in 1930, astronomers suspected that there was another planet, which would help explain Uranus’s orbit, known as Planet X.

Why we love Pluto Demoted Day

  1. Everyone likes an underdog

    As the smallest planet in the solar system, it’s easy to cheer for Pluto. For generations people were taught that there were nine planets, including Pluto, orbiting the sun. Its reclassification as a dwarf planet sparked renewed interest in Pluto and the other planets in our arm of the Milky Way galaxy.

  2. Fascination with the universe

    There is still much to learn about the solar system and the larger universe in which we live. Pluto’s demotion is a reminder that we are still always learning and investigating, not only our planet Earth but also its sister planets. As astronomers and scientists uncover new information, reclassifications like this may be necessary.

  3. Planets are fun

    Planets are a topic that interests everyone, young or old. Whether you are a child first being exposed to the solar system, or an adult with a passing interest in astrology. Much like dinosaurs, there is something inherently tantalizing about the prospect of planets and their study. Having a day to focus on the now dwarf planet Pluto is a fun excuse to geek out.

Pluto Demoted Day dates

Year Date Day
2023 August 24 Thursday
2024 August 24 Saturday
2025 August 24 Sunday
2026 August 24 Monday
2027 August 24 Tuesday