Thursday, August 17, 2006

My Very Easy Mnemonic Just Summed Up Nine Planets…erm and a Xylophone? Curses! Curses!

From the Telegraph:

Like membership of the European Union, being one of the solar system's planets used to be a matter of great prestige. But now it seems they will let any old lump of rock in.

Ceres, Charon and Xena may sound like this season's most popular chav baby names, but they are in fact two asteroids (and a moon) that within the week will be rebranded "dwarf planets". Next Thursday, 2,500 of the world's most eminent astronomers gather in Prague, and it is expected that the nine planets that orbit the Sun will become the 12.

It was previously thought that the International Astronomical Union (IAU) would instead downgrade Pluto, which since its discovery in 1930 has never really shone on the inter-planetary stage. This is hardly surprising, since it is not just 3,600 million miles from the Sun, but so tiny that its equator could quite easily be fully circled by plane without even time to enjoy an in-flight movie.

The threat of Pluto's expulsion led to a "Save Pluto" campaign by supporters, largely near the home of its discoverer, Clyde Tombaugh.

I wonder if Pluto cares.


Blogger Duck said...

If you're going to inflict British slang on us you should provide a glossary at the end of your pieces. What exactly is a "chav"? This is the second post of yours using that term.

I vote on keeping the list at 9. Once you open it up to the asteroids then you'll have people lobbying for their favorite comet. It's political correctness run amok, if you ask me.

August 17, 2006 6:47 AM  
Blogger Brit said...

Chavs are the British version of White Trash/Trailer Trash/Jerry Springer guests.

Characterised by fake Burberry baseball caps, tracksuits and cheap 'bling' jewellery.

August 17, 2006 6:51 AM  
Blogger Brit said...

PS. Google is your glossary.

August 17, 2006 6:54 AM  
Blogger David said...

Count me in on the toss Pluto movement.

But are there any astrophysicists here who can explain exactly what the Moon is? As I understand it, our Moon is not really a moon, because the Sun's gravitation is the primary force acting on it, where the primary force acting on a moon should be its primary's gravity.

Does that make the Moon actually a planet?

August 17, 2006 6:59 AM  
Blogger Duck said...

Thanks. I googled Chav and found this lovely site

Now if you had just said Hoodies, Neds, Townies, Kevs, Charvers, Steeks, Spides, Bazzas, Yarcos, Ratboys, Skangers, Scutters, Janners, Stigs, Scallies, or Hood Rats I'd have known what you were talking about.

August 17, 2006 7:32 AM  
Blogger Brit said...

Even I hadn't heard most of those words, though I know that a Hoodie is a variant seeking to hide his identity from CCTV, Townies are the binge-drinking variant and Scallies are specifically chavs from Liverpool.

We used to use Kev when I was at school because of the then remarkable prevalence of chavy boys called Kevin.

August 17, 2006 7:46 AM  
Blogger Susan's Husband said...


I would love to see a cite for that claim, as everything I have ever read on the subject puts Earth's gravity as the primary gravitational force on the Moon. The center of mass for the pair lies well below the surface of the Earth. This is not the case with Pluto/Charon, where the center of mass is about half the diameter of Pluto outside of Pluto.

On the other hand, although I'm with the "demote Pluto" crowd, I will admit that logically, the new standard is more objective.

August 17, 2006 7:47 AM  
Blogger Brit said...

I heard that about the Moon too. If Jupiter were to disappear, its moons would go in all directions, so they are moons.

Whereas if the Earth disappeared, the Moon would continue orbiting the sun, so it is not really a moon, but the Earth and Moon are a 'double planet'. Or something. I have no idea if this is important or indeed true.

August 17, 2006 7:53 AM  
Blogger Hey Skipper said...


our Moon is not really a moon, because the Sun's gravitation is the primary force acting on it, where the primary force acting on a moon should be its primary's gravity.

In a trival sense, the Sun's gravity is the primary force acting upon all the objects in the universe maintain a nearly uniform distance to the Sun over time.

This is where it is time to remember the inverse square law. The gravitational attraction between two objects is directly related to the mass of the objects, and inversely proportional to the square of the distance between them.

Because the inverse term grows so quickly, the Sun's distance means that the Moon' orbit can be calculated to a pretty accurate approximation as if the Sun didn't even exist.

August 17, 2006 8:40 AM  
Blogger Susan's Husband said...


Clearly, the issue here is relative orbital velocities, that of the system about the Sun (“solar orbital velocity”) and that of the satellite about the primary. If the latter is close to or larger than the former, then you would have the scatter effect should the primary disappear. Conversely, if the satellite orbital velocity is small compared to the solar orbital velocity, removing the primary wouldn’t have much effect.

As it turns out, you're right your first point. Approximately, Lunar orbital velocity is 1 km/s, with a solar orbital velocity of 30 km /s. In contrast, Io has an orbital velocity of 17 km/s with a solar orbital velocity of 13 km /s. So Luna would orbit the Sun roughly the same without Earth, but Io could do just about anything from continuing unchanged to dropping straight in to the Sun.

However, I do not like that definition as it depends on factors that I don’t think should matter, such as the absolute (not relative) mass of the primary, and the distance of the primary from the sun. For instance, should Luna be labeled a planet or moon based solely on how far Earth is from the Sun? After all, if you moved Earth far enough out, its solar orbital velocity could be reduced to roughly 1 km / s, or equal to Luna’s orbital velocity, demoting Luna from planet to moon. I just don’t like that sort of property in my definitional rules.

August 17, 2006 10:08 AM  
Blogger Harry Eagar said...

Some people obviously don't have enough work to keep them busy.

I was slightly surprised to learn that chavs have babies. My impression had been that they were non-breeders.

Whatever happened to the Slackers?

August 17, 2006 11:45 AM  
Blogger Brit said...

"Some people obviously don't have enough work to keep them busy."

Are you referring to the Internatiomal Astronomical Union or the Duckians?

Chavs are uber-breeders, as the lowest social classes always are.

August 17, 2006 11:50 AM  
Blogger Brit said...

Incidentally, for those of an astronomical bent, AOG has picked up on this thread on Thought Mesh.

Since I was only repeating some magazine titbit I dimly recall reading some time ago, I'm quite out of my depth with the science.

August 17, 2006 12:13 PM  
Blogger David said...

Here's the relevent Wikipedia article. It turns out that we're being timely: the Earth and Moon are now officially a Primary/Satellite system because the IAU has just adopted (as part of the process noted in the main post) a rule that a Primary/Satellite system rotate around a point within the Primary, where a double planet system rotate around a point in space.

The definition I was alluding to, under which we would be part of a double planet with the Moon, comes from Isaac Asimov. Frankly, I think it would be much cooler if Earth and Moon were a double planet, so I've decided to dissent from the new IAU definitions.

August 17, 2006 12:17 PM  
Blogger Harry Eagar said...

And what about the invasion of the basking sharks quite near Brit's pub?

August 17, 2006 5:06 PM  
Blogger Brit said...


Not just basking sharks, we've got Great Whites off the coast of Cornwall. Of course, it's all down to global warming, which is making our sharks hotter and the beer in my pub colder.

August 18, 2006 1:07 AM  
Blogger Harry Eagar said...

Uh oh. That queers my theory that the basking sharks were fleeing the sweltering Western Isles for cool Cornwall.

But if the subtropical great whites are moving into rapidly warming Cornwall, that won't work.

August 18, 2006 4:53 PM  

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