February 18 – Pluto Day

nPostednon February 18, 2014

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nQuick!nLet’s quickly celebrate Pluto, today, on the anniversary of its 1930ndiscovery by Clyde Tombaugh, before we get to the silliness of New Mexico’s new holiday, on Marchn13: Pluto is a Planet Day. (That’s awfully reminiscent of PlutonDemoted Day, which I wrote about here.)

nPlutonwas once considered a planet, because we didn’t know about all thenother objects in the solar system that are about as large as Pluto,nand that also orbit around the sun far from the gas giants. Becausenwe have discovered so many of these objects (at least one of which isnlarger than Pluto, and several of which, like Pluto, are accompaniednby moons), the International Astronomical Union decided by vote tonrelabel Pluto as a [cue dramatic horror-movie music] dwarf planet. n

nWhichnis so not a big deal, right? Yet some people still get upset aboutnthis so-called demotion…

Othernlabels for Pluto are Plutoid and Kuiper Belt Object. Basically,nPlutoids are dwarf planets that lie beyond (or mostly beyond) the gasngiants (as opposed to the only dwarf planet in the asteroid belt,nCeres). Plutoids are the Kuiper Belt Objects that are large enough tonbe near-spherical—most KBOs are shaped more like potatoes or othernknobbly shapes.

nGooglensays about Pluto:

Plutonis the largest known object in the Kuiper Belt…

…thententh largest body observed directly orbiting the Sun (as opposed tonorbiting a planet)…

…andnthe second largest known dwarf planet…

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nOkay,nnow back to Pluto’s discovery:

nOncenupon a time there was a wealthy man who loved astronomy. His name wasnPercival Lowell. He had heard that scientists had carefully observednNeptune’s orbit around the Sun and had decided that it was possiblenthat yet another planet, even farther away than Neptune, was alsondisturbing Uranus’s orbit. Scientists speculated that there might bena ninth planet circling the Sun.

nLowellnwanted to discover that possible ninth planet, which he called PlanetnX. He founded the Lowell Observatory in Flagstaff, Arizona, and henstarted a project in search of Planet X. From 1906 to Lowell’s deathnin 1916, they searched but didn’t find a ninth planet.

WhennLowell died, he left a lot of money to his wife Constance (ofncourse), but he also left a million dollars to “his” observatorynto keep up the search for Planet X.

nButnConstance didn’t care a whit about Planet X. She wanted the millionndollars for herself! So she contested the will and dribbled away mostnof the money in court fees. She finally (ten years later!) lost thencase, and the director of the observatory asked a young astronomernnamed Clyde Tombaugh to resume the search for the ninth planet.

nTombaughnwas just 23 years old at the time.

nTombaughnused a machine called a blink comparator. He quickly shifted back andnforth between two photos of the night skies that were taken of thensame spot in the sky but two weeks apart. What he was looking for wasnsomething that had changed position or appearance in those two weeks.

nFinally,nafter more than a year of blink-comparator searching, Tombaughndiscovered a teeny light that had, as expected moved. More searchingnof other photographic plates revealed that the new thing did indeednmove as a planet should. The news shot around the world: a ninthnplanet had been discovered!

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nBynthe way, loads of suggestions for the new name poured in; evennConstance Lowell made suggestions! Even though she had almostnsingle-handedly wrecked the planet-finding project by taking thenLowell Observatory to court, she asked that the new planet be callednZeus (even though Jupiter is named after that same god—the planetsnuse the Roman, not the Greek, names for the ancient gods andngoddesses), and then she suggested Percival, and then she suggested –nwait for it! – Constance!

nGag!

nLuckily,nthe observatory director ignored her suggestions and chose a Romanngod who had not yet been assigned a planet: Pluto, god of thenunderworld, the Roman name for the Greek god Hades. n

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