Today is officially “Presidents' Day” on your calendar, but February 18 is also the date in history when Pluto was discovered at Lowell Observatory in Flagstaff, Ariz.

Percival Lowell, the founder of the observatory that bears his name, had long postulated on the existence of a 9th planet in our solar system. And although he died in 1916 before it could be found, the search for additional planets and asteroids continued in Flagstaff.

One of those doing the looking was 20-year-old Clyde W. Tombaugh, a Midwestern farm boy who had always been interested in the stars, not the earth. His college plans were delayed after a hailstorm destroyed the crops on his parents’ Kansas farm, but he was undeterred.

When he’d exhausted the limitations of his Sears & Roebuck-purchased telescope, young Clyde built one of his own. He mailed the specs to the scientists at Lowell Observatory seeking feedback. Instead, the impressed astronomers offered him a job, and off he went.

After finding a 9th planet on Feb. 18, 1930, scientists in Flagstaff were in no hurry to name it. The celestial body had been around for billions of years, so waiting a few weeks to get the name just right seemed prudent.

As word of this exciting discovery flashed around the world, those in the science community began to offer their own nominations. At a breakfast table halfway around the world in Oxford, England, retired university librarian Falconer Madan read a story in the Times of London aloud to his 11-year-old granddaughter, Venetia Burney.

That article, which ran on Page 14, noted that the planet was still unnamed. “I think Pluto would be a good name for it,” Venetia opined.

Granddad agreed, and he passed her idea along to Oxford University astronomer Herbert Hall Turner, who pronounced it “excellent.” Turner sent a cable to Lowell Observatory: “Naming new planet, please consider PLUTO, suggested by small girl Venetia Burney for dark and gloomy planet.”

In Flagstaff, the name struck a chord with Clyde Tombaugh. Not only did it seem fitting for such a remote sphere, but Pluto’s first two letters offered subtle homage to Percival Lowell. And so, in May 1930, it became official.

Pluto’s name would stick, but as astronomers learned more about it, it would not keep its exalted status.

For one thing, Pluto is not always the most distant planet. It’s so far away that it takes 248 years to orbit the sun, and during part of that time, Neptune is actually closer to the sun. It was during one of these periods – the late 1970s to the late 1990s – that astronomers were able to learn much more about Pluto.

It has an atmosphere, which freezes and thaws depending on how far away it is from the sun; little or no magnetic field; and a very close and relatively large moon, which was discovered in 1978 and named Charon.

In 2005, the Hubble Space Telescope found two more moons, Nix and Hydra, both of which are part of what is now called the Kuiper Belt. (In 2006, NASA dispatched the New Horizons spacecraft to explore the asteroid field; the ship is expected to reach its destination in 2015.) Also, in 2006, Pluto was officially relegated to the status of “dwarf planet,” a designation it shares with Charon and which – let’s be honest – just sounds less prestigious.

Although he lived to be 90, Clyde Tombaugh, didn’t survive long enough to see his planet demoted. But his widow said he would have understood.

“He was a scientist,” she said. “He would understand they had a real problem when they start finding several of these [asteroids] flying around the place.”

Venetia Burney also lived to be 90, and she was also philosophical. She conceded she would rather have Pluto keep its designation as a planet, but late in life she was more vexed by another claim: that she’d gotten the name from Walt Disney’s cartoon character of the same name instead of her youthful studies of Roman mythology.

As it happened, “Pluto” the dog did indeed appear in 1930, but some Hollywood history sleuthing showed that his original name was “Rover” -- and he wasn’t renamed Pluto until the cartoon “Moose Hunt,” which wasn’t released until April 1931.

“It has now been satisfactorily proven that the dog was named after the planet, rather than the other way around,” Venetia told the BBC in 2006. “So, one is vindicated.”