Human Journey

Pluto’s 80th “Anniversary”


Pluto and its moon, Charon

—Picture courtesy Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI)

On January 23, 1930, a camera at the Lowell Observatory in Flagstaff, Arizona, took the first of two pictures that would add [at least for a while] a ninth planet to our solar system.

A few months earlier, Kansas native Clyde Tombaugh had been hired by the observatory to search for what was then being called Planet X.

The observatory’s founder, Percival Lowell, had theorized that Planet X was out there and would exert some sort of gravitational influence on Uranus and Neptune.

During his lifetime, Lowell calculated where he thought the mystery planet should be and funded three separate searches for its whereabouts.

Although Lowell died unsatisfied in 1916, his fellows at the observatory continued the search and even built a special camera in 1929 for that purpose.


Tombaugh and a telescope

—Photograph courtesy NASA

The idea was to take pictures of the night sky along what’s known as the ecliptic plane, the band in the sky where most of the other planets orbit, and see if anything moved.

Sure, stars do migrate across the sky as Earth rotates. But the points of light stay in fixed positions relative to each other—making, for example, constellations possible.

However, the ancients noted that some stars “wandered” across the sky, popping up in different constellations over time. These wandering stars, we now know, are the other planets orbiting the sun.

Tombaugh’s job was to compare one picture from the camera with another taken a few days later using what’s called a blink comparator.

This device toggles between two images, kinda like a person quickly closing one eye then the other, to reveal any differences.

When Tombaugh loaded up the January 23 picture of the constellation Gemini with another taken on January 29, this is roughly what he saw:


Did you see it? That itteh bitteh dot is moving.

Ironically, Pluto is so itteh bitteh that it doesn’t really affect Uranus or Neptune at all: Lowell was wrong on that count, which makes it even more amazing that Tombaugh found the darn thing.

Now technically our man Clyde didn’t look at the two January pictures until February 18, 1930, so that’s the true anniversary of Planet X’s discovery. Later that year the planet was officially named Pluto, on the suggestion of an 11-year-old British lass.

Of course, not too long ago Pluto was deemed no longer a planet—although a few die-hards continue to champion the ousted world.

No matter what you call it, Pluto is one interesting body, which is why NASA has a spaceship called New Horizons zooming toward it and its Kuiper Belt companions even now.

New Horizons, by the by, launched four years ago this past Tuesday, and is slated to arrive at Pluto in 2014.


New Horizons lifts off from Kennedy Space Center

—Photograph by Scott Andrews, NIKON via NASA

The mission should answer some lingering questions about just what is this Pluto thing anyway and how does it fit in the solar system’s family album?

In the meantime, I’m gonna take a moment of silence on Saturday to honor Tombaugh and his persistent blinking. Pluto may be a dwarf planet now, Clyde baby, but you’re still the first American to discover a planet in my book.

  • Laurel Kornfeld

    It is more than “a few diehards” who continue to reject the controversial IAU demotion of Pluto. Please do not blindly accept that decision as fact, as it was voted on by only four percent of the organization’s members, most of whom are not planetary scientists. It was immediately rejected by hundreds of professional astronomers led by New Horizons Principal Investigator Dr. Alan Stern. There are strong scientific reasons for keeping Pluto a planet, as it is in hydrostatic equilibrium and orbits the Sun. It is simply the first of a third class of planets, the dwarf planets (the first two being terrestrials and jovians).

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