June 22 – A Moon for Pluto!

Posted on June 22, 2015

What was up with Pluto?

That's what U.S. Naval Observatory astronomer James Christy was wondering as he studied Pluto through a telescope. It looked...bulgy!

Left, Pluto bulgy.
Right, Pluto round
and non-bulgy.

As Christy continued to make observations, he realized that the bulginess was different at different times. It didn't make sense that Pluto itself would be have a bulge that moved around its middle and sometimes disappeared. It made more sense that Pluto had a companion whose reflected sunlight seemed to merge with the sunlight reflecting from Pluto.

Christy made this discovery on this date in 1978. The discovery was announced to the world in early July.

Actually, others had a chance to make the discovery. Christy wanted to check his observation, and he was able to discover the periodic Pluto-bulges in photos taken of the planetoid as far back as 1965. For more than a decade, nobody had noticed the teeny elongation.

Pluto is tiny, but Charon is large.

You've probably heard that Pluto is so teeny that it lost its former label of planet and is now considered a dwarf planet, planetoid, or Plutoid. As a matter of fact, Pluto is the second largest of the Plutoids in our solar system (only Ceres is larger).

But Charon is a bit more than half the size of Pluto. (Compare this to Earth's moon, which is only a tiny fraction of the size of the Earth.) Charon isn't all that large compared to other solar system moons (even Pluto is smaller than Earth's Moon, let alone Charon!) - but the two are much closer in size than are other planet-satellite comparisons.

What's in a name?

Ancient peoples had various names for the five planets that they could see with their naked eyes, but European scientists ended up using the names used by Ancient Roman astronomers. Those names were the names of their gods and goddesses: Venus, Mars, Mercury, Jupiter, and Saturn. When more planets were discovered in the modern era, scientists decided to maintain the custom of naming the planets after Roman deities. That's how we ended up with Uranus, Neptune, and Pluto.

Pluto is the Roman name for the Roman god of the underworld, the god who the Greeks called Hades.

One of the beings associated with Pluto-the-Roman-god is Charon. Charon is the ferryman who transported the dead to the underworld. Coincidentally, the guy who discovered Pluto's moon—and therefore got to name it—had a wife named Charlene. He called her “Char.” Christy loved the nod to his wife while sticking to Roman mythological sources for the name of his discovery.

But the Greeks pronounced “Ch” as a hard “K” – and so the name of the Roman ferryman was pronounced Karon. And Christy's wife's name had “Ch” pronounced like “Sh” – “Shar” for “Sharlene.” This explains why many speakers of other languages, and also many English-speaking astronomers, call Pluto's moon “Karon,” but some English-speaking astronomers, the discoverer himself, and NASA all pronounce the name “Sharon.”

Actually, the two different ways of pronouncing the name has led to the “Sh” version being a shibboleth of sorts. A shibboleth is a version or pronunciation of a word that is used by an in-group, the people “in the know.”

Also on this date:

Anniversary of the patenting of a pin-making machine 

Midsummer in Sweden

Schoolteachers' Day in El Salvador

Anniversary of the lowering the voting age in the U.S.

Explorer George Vancouver's birthday

Plan ahead:

Check out my Pinterest boards for:

• June holidays

• June birthdays

• Historical anniversaries in June

And here are my Pinterest boards for:

• July holidays

• July birthdays

• Historical anniversaries in July 

February 18 – Pluto Day

Posted on February 18, 2014

Quick! Let's quickly celebrate Pluto, today, on the anniversary of its 1930 discovery by Clyde Tombaugh, before we get to the silliness of New Mexico's new holiday, on March 13: Pluto is a Planet Day. (That's awfully reminiscent of Pluto Demoted Day, which I wrote about here.)

Pluto was once considered a planet, because we didn't know about all the other objects in the solar system that are about as large as Pluto, and that also orbit around the sun far from the gas giants. Because we have discovered so many of these objects (at least one of which is larger than Pluto, and several of which, like Pluto, are accompanied by moons), the International Astronomical Union decided by vote to relabel Pluto as a [cue dramatic horror-movie music] dwarf planet.

Which is so not a big deal, right? Yet some people still get upset about this so-called demotion...

Other labels for Pluto are Plutoid and Kuiper Belt Object. Basically, Plutoids are dwarf planets that lie beyond (or mostly beyond) the gas giants (as opposed to the only dwarf planet in the asteroid belt, Ceres). Plutoids are the Kuiper Belt Objects that are large enough to be near-spherical—most KBOs are shaped more like potatoes or other knobbly shapes.

Google says about Pluto:

• Pluto is the largest known object in the Kuiper Belt...
• ...the tenth largest body observed directly orbiting the Sun (as opposed to orbiting a planet)...
• ...and the second largest known dwarf planet...

Okay, now back to Pluto's discovery:

Once upon a time there was a wealthy man who loved astronomy. His name was Percival Lowell. He had heard that scientists had carefully observed Neptune's orbit around the Sun and had decided that it was possible that yet another planet, even farther away than Neptune, was also disturbing Uranus's orbit. Scientists speculated that there might be a ninth planet circling the Sun.

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

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

But Constance didn't care a whit about Planet X. She wanted the million dollars for herself! So she contested the will and dribbled away most of the money in court fees. She finally (ten years later!) lost the case, and the director of the observatory asked a young astronomer named Clyde Tombaugh to resume the search for the ninth planet.

Tombaugh was just 23 years old at the time.

Tombaugh used a machine called a blink comparator. He quickly shifted back and forth between two photos of the night skies that were taken of the same spot in the sky but two weeks apart. What he was looking for was something that had changed position or appearance in those two weeks.

Finally, after more than a year of blink-comparator searching, Tombaugh discovered a teeny light that had, as expected moved. More searching of other photographic plates revealed that the new thing did indeed move as a planet should. The news shot around the world: a ninth planet had been discovered!

By the way, loads of suggestions for the new name poured in; even Constance Lowell made suggestions! Even though she had almost single-handedly wrecked the planet-finding project by taking the Lowell Observatory to court, she asked that the new planet be called Zeus (even though Jupiter is named after that same god—the planets use the Roman, not the Greek, names for the ancient gods and goddesses), and then she suggested Percival, and then she suggested – wait for it! – Constance!

Gag!

Luckily, the observatory director ignored her suggestions and chose a Roman god who had not yet been assigned a planet: Pluto, god of the underworld, the Roman name for the Greek god Hades.

Also on this date:

Cow Milked While Flying in an Airplane Day 

Battery Day 

Stained-glass artist Louis Comfort Tiffany's birthday

Anniversary of the invention of the modern vacuum

Plan ahead:

Check out my Pinterest boards for:

• February holidays 
• February birthdays 

• Historical anniversaries in February

And here are my Pinterest boards for:

• March holidays 
• March birthdays 
• Historical anniversaries in March

August 24, 2012 - Pluto Demoted Day

The news shocked the world. (Apparently.) 

Kids cried. Adults grumbled. People wrote irate Letters to the Editor. (Umm...really?)

All because poor little Pluto, so small and far away, and so incapable of defending itself, was kicked out of the planet family!

It was demoted to—gasp! the horror!—dwarf planet!!!

Back on August 24, 2006, when the International Astronomical Union voted to relabel Pluto based on many new findings in astronomy, I nodded my head. New data often requires us to re-sort, re-categorize, re-label. It's something to cheer, because it means we humans have learned more; we're closer to achieving an accurate picture of the universe.

But some people got very upset! Some children sent hate mail to astronomer Neil deGrasse Tyson. Legislatures of two states voted to refuse to recognize the IAU's decision. People “yelled” at each other on the internet (and you know how rarely THAT happens!).

One of the reasons that some people got upset, apparently, is because Pluto getting kicked out of planethood messes up the mnemonics that kids learn to remember the order of the planets in the solar system. One of the most common of these mnemonics is: “My Very Energetic Mother Just Served Us Nine Pizzas.” (Mercury – Venus – Earth – Mars – Jupiter – Saturn – Uranus – Neptune – Pluto.)

But this is silly. For one thing, Pluto sometimes dips inside Neptune's orbit, and making the sentence end with the words “served us pizzas nine” sounds pretty goofy. (If Pluto were a planet, it would have been the eighth, not ninth, planet from 1979 to 1999.) Also, surely we can easily come up with a new mnemonic? How about “My Very Energetic Mother Just Served Us Nachos,” or even “My Very Easygoing Mother Just Served Us Nothing”?

I gather that it is Americans, and American school children, that got especially upset about Pluto's demotion. The guy who discovered Pluto, Clyde Tombaugh, was an American astronomer, and Walt Disney named Mickey Mouse's dog “Pluto” after the planet to celebrate that discovery. Maybe a lot of people were upset by Pluto being kicked out of the planet club because it is the smallest planet (by far—it's really tiny, even compared to the very small Mercury), and people want to stick up for the little guy, and root for the underdog.

To which some people have replied, “Why are you getting so upset about this? You don't hear Pluto complaining, do you?”

And some people have pointed out that, it's not as if Pluto were blown up, or ejected out of the solar system. It's just where it always has been. We just have added the word "dwarf" to its category.

Hmmm...so what is a planet?

The IAU was struggling with the question of whether or not to call some newly discovered bodies planets. Eris, Makemake, and Haumea all orbit far from the Sun, like Pluto, they're spherical, like Pluto, and some of them are roughly the size of Pluto. If Pluto is a planet, shouldn't they be planets, too?

So, does the solar system have 10 planets? Or 12? Or more and more as we discover more and more?

(If so, we're gonna need a much bigger mnemonic!)

Some scientists reasoned that Pluto and these other Kuiper Belt Objects could be considered a new sort of thing in the solar system. Instead of being the last and littlest planet, Pluto could be thought of as the first and one of the largest Plutoids (KBOs that are large enough to be roughly spherical in shape).

See, it's not a DEmotion, it's a PROmotion!

The definition of a planet is:

• an object that circles a star (the IAU definition said “that circles the sun,” but that was a mistake that would leave out all of the planets we have discovered circling other stars)
• an object large enough to be spherical
• an object that has “cleared the neighborhood” around its orbit. That would exclude the largest asteroids in the asteroid belt as well as the largest Plutoids in the Kuiper belt.

Also on this date:

Independence Day in the Ukraine 

Anniversary of the eruption of Mt. Vesuvius 

February 4, 2011

Happy Birthday, Clyde Tombaugh

How would you like to be the first person to discover a dwarf planet? How'd you like to be the only person in the twentieth century to discover a planet? How about being the one who discovers the first Kuiper Belt Object?

Clyde Tombaugh, who was born on this day in 1906, got to be all three...all because he discovered Pluto!

During Tombaugh's lifetime, Pluto was considered the ninth planet.

Because of recent discoveries of many other objects from as far away as the orbit of Neptune out to 55 A.U. from the sun, astronomers decided that Pluto was just a large-sized example of an rocky/icy body in an entire wide belt of rocky/icy bodies. This belt is called the Kuiper Belt, and so Pluto is now considered a Kuiper Belt Object (KBO).

When I say that there are “many” KBOs...I'm talking thousands! There are more than 70,000 KBOs that are larger than 100 km (62 miles) in diameter. Several of these KBOs are large enough to be considered dwarf planets: Eris (which is larger than Pluto), Pluto, Haumea, and Makemake. Some of the moons of planets (such as Neptune's Triton and Saturn's Phoebe) are considered to have once been KBOs, and the dwarf planet Pluto has a relatively large moon, Charon, plus two smaller moons, Nix and Hydra, that are of course also KBOs.

So Pluto was a planet and is now a Kuiper Belt Object and a dwarf planet—and Clyde Tombaugh's guarantee of inclusion in the history books.

By the way...

• Another name for a dwarf planet that is in the Kuiper Belt is plutoid. So we could also say that Tombaugh discovered the first plutoid!

• Tombaugh was just 24 years old when he discovered Pluto.

• Tombaugh wanted to go to college, but hailstones ruined his family's crops and spoiled his hopes for being able to afford it. He didn't give up! He built several telescopes, grinding the lenses and mirrors himself, and he sent drawings of Jupiter, Mars, and the telescopes to the Lowell Observatory in Arizona. This bold move resulted in Tombaugh being offered a job in 1929. It was on the job as an astronomer that Tombaugh made his big discovery.

After discovering Pluto, Tombaugh was able to finally go to college (apparently while still keeping his job). He ended up getting both a bachelor's and a master's degree in astronomy.

• Tombaugh discovered nearly 800 asteroids, a comet, hundreds of variable stars, star clusters, galaxy clusters, and a galaxy supercluster.

• Tombaugh helped to choose the name Pluto, but he didn't think of the name himself. Instead, a little girl, age 11, who lived in far-away England, made the suggestion... Venetia Katharine Douglas Burney was excited about the discovery of a ninth planet and suggested the name Pluto, who was the Roman god of the underworld. It seems that Burney made that particular suggestion partly because the other planets are named for Roman gods and partly because Pluto-the-god had the power to turn himself invisible—and Pluto-the-planet had been so hard to discover, it was as if it had the power of invisibility.

One reason Tombaugh liked and chose the name Pluto is because the first two letters, P and L, are the initials of the astronomer who predicted that there would be a planet beyond the orbit of Neptune. Percival Lowell was a wealthy man who founded the observatory in which Tombaugh worked and who urged the search for “Planet X,” which, Lowell claimed, slightly displaced both Uranus and Neptune from their orbits. Unfortunately, Lowell died at age 61, fourteen years before Planet X was discovered and named Pluto.

Pluto has four known moons.

Poor Pluto?

A lot of people seem to be upset that Pluto has been “demoted” from being a planet to being a mere dwarf planet. They seem to feel hurt on behalf of poor Pluto, as if they were worrying about the feelings of Mickey Mouse's beloved dog Pluto. (By the way, the Disney pup Pluto was named after the planet/dwarf planet—the whole world was excited by its discovery!)

If you worry about poor Pluto, read this clear and accurate explanation why the new label for Pluto as a dwarf planet is better science. 

Remember, as Fraser Cain clearly points out in the link above, one of the recently discovered Kuiper Belt Objects is larger than Pluto. If Pluto were to still be considered a planet, Eris would have to be, too. No matter what, we can't hold onto a solar system with nine planets—at this point, we can either have 8 or we can have 10, 12, or more—depending on where you draw the cut-off line of size between planets and dwarf planets. Astronomers have decided on a good, solid definition for planet that dictates that the solar system has 8 planets.

• Another way to find out about the Pluto-planet controversy is by playing a game on the National Geographic Kids website. 

• NASA has a gallery of images of Pluto and KBOs. 

• For more on the Kuiper Belt, check out this earlier post.