PLUTO DAY – February 17

Pluto Day - February 18
(Last Updated On: November 8, 2022)


Every year, Pluto Day on February 18th celebrates the discovery of the former planet. Up until 2006, the dwarf planet was considered one of the nine planets in the solar system.

Clyde Tombaugh, an American astronomer, discovered Pluto. He made the discovery at the Lowell Observatory on February 18th, 1930 84 years after the discovery of Neptune. Pluto was named for the Roman god of the Underworld.

The name also honors Percival Lowell. His initials are the first two letters of Pluto. Lowell was an American astronomer who believed there was another planet beyond Neptune. He initiated the search that led to the discovery of Pluto. On March 19, 1930, Lowell Observatory officially announced the discovery of a 9th planet.

Planet or Not a Planet?

On August 24th, 2006, the International Astronomical Union (IAU) reduced Pluto to a dwarf planet. The IAU determined that Pluto failed to meet certain criteria that defined it as a full-sized planet. A full-sized planet must:

  1. Orbit the sun
  2. Have sufficient mass to assume hydrostatic equilibrium
  3. Clear the neighborhood around its orbit

Pluto meets the first two criteria, but not the third. In other words, there are no other bodies of comparable size under its gravitational influence. Also, modern technology has allowed astronomers to discover other bodies in space that are the same size or larger than Pluto. While hundreds of dwarf planets exist, the IAU only officially recognizes five of them. They include Ceres, Pluto, Eris, Haumea, and Makemake.

Despite these facts, scientists and the general public, have had a hard time accepting the idea that Pluto is no longer a planet. Many people remember the mnemonic, “My Very Educated Mother Just Served Us Nine Pizzas.” The first letter in each world helped them to remember the order of the planets. The “P” in Pizza, referred to Pluto. The mnemonic was changed to “My Very Educated Mother Just Served Us Noodles.”

Just because it is no longer a planet, you can still learn interesting facts about Pluto:

  • Since its discovery, Pluto has not made a complete orbit around the sun.
  • It has five known moons.
  • Pluto’s extremely thin atmosphere consists mostly of nitrogen.
  • One day on Pluto equals 6.4 days on Earth.
  • It has ice mountains that are taller than the Rockies.


Planetariums, observatories, and other places that study the solar system hold special events on this day. To participate:

  • Set up your own telescope and try to find Pluto.
  • Learn more about planets and dwarf planets.
  • If you think Pluto should still be a planet, write about it or discuss it with others.
  • Watch a documentary about Pluto, such as The Year of Pluto, Mission Pluto, or Chasing Pluto.
  • Find educational videos about Pluto on the Internet.

No matter what you do, share your support of this dwarf planet on social media with #PlutoDay.


Pluto Day commemorates the anniversary of its discovery each year on February 18th, 1930.

Join the

Stay up to date on upcoming national days and Celebrate Every Day!