Significant figures

[jdaw1]

Split from another form of drivel.

convinced the praticioners of certain religions that the Earth is, in fact, more than 6000 years old.

Traditionally dated to 4004 BC (see, amongst many others, AnswersInGenesis.org). As we’re now in 2015 AD, they accept almost two decades more than 6000 years. QED.

[Glenn E.]

convinced the praticioners of certain religions that the Earth is, in fact, more than 6000 years old.

Traditionally dated to 4004 BC (see, amongst many others, AnswersInGenesis.org). As we’re now in 2015 AD, they accept almost two decades more than 6000 years. QED.

Too many significant digits. I used one, you get one. Your decades are lost as rounding errors.

[jdaw1]

convinced the praticioners of certain religions that the Earth is, in fact, more than 6000 years old.

Traditionally dated to 4004 BC (see, amongst many others, AnswersInGenesis.org). As we’re now in 2015 AD, they accept almost two decades more than 6000 years. QED.

Too many significant digits. I used one, you get one. Your decades are lost as rounding errors.

Oh, you meant six millennia. In which case, very fair, even if slightly confused by you writing “6000 years”. Which, silly me, I took to mean 6000 years.

[Glenn E.]

convinced the praticioners of certain religions that the Earth is, in fact, more than 6000 years old.

Traditionally dated to 4004 BC (see, amongst many others, AnswersInGenesis.org). As we’re now in 2015 AD, they accept almost two decades more than 6000 years. QED.

Too many significant digits. I used one, you get one. Your decades are lost as rounding errors.

Oh, you meant six millennia. In which case, very fair, even if slightly confused by you writing “6000 years”. Which, silly me, I took to mean 6000 years.

No, I meant 6000 years. Not 6000.0 years.

Perhaps you do it differently in the UK, but here in 'Murica trailing zeros are not considered significant unless followed by a decimal point.

[jdaw1]

Perhaps you do it differently in the UK, but here in 'Murica trailing zeros are not considered significant unless followed by a decimal point.

Here on ThePortForum, if I sell you 600 bottles of Fonseca 1970 and deliver only 590, grumbling would be expected. Likewise with dates: offering for sale a 1980 but delivering a 1978 would also cause unhappiness.

(Should this conversation be split? Or just ended? Or both?)

[PhilW]

Perhaps you do it differently in the UK, but here in 'Murica trailing zeros are not considered significant unless followed by a decimal point.

Entirely correct, BUT you have to state how many significant digits are present, which you did not, otherwise all digits are assumed to be significant.

Here on ThePortForum, if I sell you 600 bottles of Fonseca 1970 and deliver only 590, grumbling would be expected.

Please do. Dependent on the price there could be no grumbling at all, even if you are 100 bottles short - though a diatribe on numeracy would be highly likely.

[Glenn E.]

Perhaps you do it differently in the UK, but here in 'Murica trailing zeros are not considered significant unless followed by a decimal point.

Entirely correct, BUT you have to state how many significant digits are present, which you did not, otherwise all digits are assumed to be significant.

Unless and until pedantry kicks in.

A neutral 3rd party expert witness has commented, so I withdraw. In the future jdaw1 may interpret my use of "planet" in reference to Pluto has a shorter and easier to type abbreviated form of "dwarf planet".

[jdaw1]

In the future jdaw1 may interpret my use of "planet" in reference to Pluto has a shorter and easier to type abbreviated form of "dwarf planet".

Now this off-topic drivel has been split from the topic from which it was off (aside to the aside of the aside: I’m loving the prepositional torture), we can do the Pluto-is-Pluto-isn’t rant. I’ll show my cards: the Stern–Levison parameter Λ is an excellent distinction between proper planets and things too small to be proper planets.

[PhilW]

But... is or is not a dwarf planet a subtype of planet?

[jdaw1]

But... is or is not a dwarf planet a subtype of planet?

Not.

[PhilW]

Daft naming convention then...

[jdaw1]

Daft naming convention then...

If you are going to spend your days remarking on what is stupid in the world, expect to be very busy. (Whether or not you contribute to the cricket/ashes thread.)

[Glenn E.]

In the future jdaw1 may interpret my use of "planet" in reference to Pluto has a shorter and easier to type abbreviated form of "dwarf planet".

Now this off-topic drivel has been split from the topic from which it was off (aside to the aside of the aside: I’m loving the prepositional torture), we can do the Pluto-is-Pluto-isn’t rant. I’ll show my cards: the Stern–Levison parameter Λ is an excellent distinction between proper planets and things too small to be proper planets.

When the definition of a "planet" requires a special clause to allow Earth, Mars, Jupiter, and Neptune to qualify - but not Pluto - then it is a bad definition.

[jdaw1]

When the definition of a "planet" requires a special clause to allow Earth, Mars, Jupiter, and Neptune to qualify - but not Pluto - then it is a bad definition.

If that were true, it would be a bad definition. But it isn’t.

Λ = k × M² / P, where M = mass, P = orbital period, and k is effectively a constant. For the real planets, it’s much much chunkier than 1. For the non-planets, much much smaller. Of the planets, smallest for Mars, at ≈942. Of the non-planets, largest for Pluto at ≈0.00295 then Eris at ≈0.00215. That’s robust.

[DRT]

When the definition of a "planet" requires a special clause to allow Earth, Mars, Jupiter, and Neptune to qualify - but not Pluto - then it is a bad definition.

If that were true, it would be a bad definition. But it isn’t.

Λ = k × M² / P, where M = mass, P = orbital period, and k is effectively a constant. For the real planets, it’s much much chunkier than 1. For the non-planets, much much smaller. Of the planets, smallest for Mars, at ≈942. Of the non-planets, largest for Pluto at ≈0.00295 then Eris at ≈0.00215. That’s robust.

I read the wiki and I agree with Glenn. I do not understand the detail of the maths, but the line has been drawn in a place where some things are planets and some things are not. That line could equally have well been drawn in a place where the gas giants were planets and the rocks like Earth were not. That is subjective judgement, not a fact.

This is a case of science trying to impose a meaningless rule and then trying to defend itself with flawed logic.

[jdaw1]

That line could equally have well been drawn in a place where the gas giants were planets and the rocks like Earth were not.

If true, a powerful argument. But not so. Things bigger than 1 are massively bigger than 1, things smaller are very much smaller. No close cases.

Λ determines whether things gravitationally dominate their neighbourhood. Only one thing can. For instance, Jupiter can have Trojans in its Lagrange point, and they’re stable. But if the Trojans should reach ≈10%ish of the mass of the dominant body, things become unstable. So three cases possible.
• Largest object in this orbit large enough for Λ>>1, and Trojans small. Stable. Largest object a planet. Hurray!
• Largest object in this orbit large enough for Λ>>1, and Trojans >10% of largest object. Unstable — quickly falls apart. Problem case doesn’t last long.
• Largest object in this orbit has Λ<<1, so has too little effect on other bodies to dominate them. Welcome to the asteroid belt / Kuiper belt / etc.

[Glenn E.]

We argue not with the math, but rather with the choice to use that particular line in the sand as the definition. There is no scientific reason to define a planet as an object that clears its orbit, or that when it fails to clear its orbit like Earth, Mars, Jupiter, Neptune, and Pluto, said orbit is stable which conveniently excludes Pluto.

[jdaw1]

I agree that the phrasing ‘clearing the neighbourhood’ is wrong. It should be ‘dominating the neighbourhood’.

Let’s start elsewhere. Do you agree that many asteroids are not planets? If you think that every pebble in solar orbit is a planet, then the nature of the disagreement is clear. If not, then there are some solar-orbiting natural things that are deemed planets, and some that are not. How would you draw the line?

The problem, as I understand it, is a shortage of more plausible lines. Suggest one.

[DRT]

I think the geological processes that affect an object is a more plausible argument.

Asteroids and most moons are inert lumps of rock and other stuff. The planets that we call planets plus Pluto are the only objects we know of that are (a) not a satellite of a planet and (b) are or once were geologically active.

I think that would be a better basis than arbitrary maths that don't really mean anything.

[jdaw1]

I think the geological processes that affect an object is a more plausible argument.

Asteroids and most moons are inert lumps of rock and other stuff. The planets that we call planets plus Pluto are the only objects we know of that are (a) not a satellite of a planet and (b) are or once were geologically active.

I think that would be a better basis than arbitrary maths that don't really mean anything.

The maths has meaning, but this also has merit. And problems.

• Is Eris a planet? Under the DRT definition, the answer has to be ‘no idea’. And no prospect of having an idea for what might be ages. Ditto lots of others.

• If a planet is shattered in an impact, is every pieces of shrapnel (all which have been formed or shaped or changed by geological processes) then a planet?

[Glenn E.]

I agree that the phrasing ‘clearing the neighbourhood’ is wrong. It should be ‘dominating the neighbourhood’.

I imagine the meeting where a bunch of astronomers suddenly realized that Earth was no longer considered a planet, and so frantically changed the definition to "dominating" from "clearing" the neighborhood.

"Planet" is a loaded term at this point. If gas giants and telluric objects can both be considered planets simply because they always have been, then there's no reason to create a "scientific" definition that explicitly excludes Pluto. Especially when said definition is explicitly restricted to our solar system. If Astronomers need such a definition (note: they clearly don't since the definition is restricted to our solar system, which isn't going to get any bigger during our lifetimes), they can use a different word. Feel free to make one up that everyone else can ignore.

Re: Eris - "we don't know yet" is a perfectly acceptable answer to "is Eris a planet?"

Further ramblings... what are all these things orbiting other stars? Can't use the IAU definition, so do we have to stop calling them planets? (Hint: yes. Which is dumb.)

[jdaw1]

I am defending the definition as it applies to our home. It should also apply to other solar systems, at least those with a single sun. Multiples, especially non-hierarchical multiples, might be weird.

[DRT]

I am defending the definition as it applies to our home. It should also apply to other solar systems, at least those with a single sun. Multiples, especially non-hierarchical multiples, might be weird.

Or you might just be supporting the making it up as we go along theory. Well done.

The Earth is not flat, and a planet has no scientifically meaningful definition.

Make it up from there.

[jdaw1]

and a planet has no scientifically meaningful definition.

A particular planet does not, but the word ‘planet’ could.

Re: Eris - "we don't know yet" is a perfectly acceptable answer to "is Eris a planet?"

Yes, sure. But in that case Pluto would not have been a planet until a few days ago. Is that what you want? Do you want there to have been only one planet until the space age?

[Glenn E.]

Re: Eris - "we don't know yet" is a perfectly acceptable answer to "is Eris a planet?"

Yes, sure. But in that case Pluto would not have been a planet until a few days ago. Is that what you want? Do you want there to have been only one planet until the space age?

You extrapolate; I did not. I'm perfectly happy saying "our understanding of the solar system is evolving, so for the time being we cannot say for sure whether or not Eris should be considered a planet or some other type of solar object."

I'm far from convinced that our evolving understanding of the solar system needs to have a new definition of a "planet" that seems to have been deliberately created to exclude Pluto. Please explain the need for this new definition before we argue whether or not it is correct. I see no need, ergo the question of whether or not it is correct is moot.

[jdaw1]

that seems to have been deliberately created to exclude Pluto.

What is the evidence of this deliberate exclusion? A bright line was found, a logical and natural bright line, and used. Eight things lay on one side of it, not nine. That’s not deliberate exclusion.

With the discovery of lots of large-ish KBOs, a definition was needed.
• That definition could have been the current definition of a dwarf planet: directly orbiting sun, big enough to be rounded by gravity. That would make Pluto and may other KBOs into planets. Sure. Would you have preferred that? (I don’t strongly object.)
• Or it could be the sensible definition involving gravitational domination.
• Or, perhaps my favourite, it could be the previous “plus the nine objects that were, prior to 2006, called planets”.
• Or a better bright line. What?

[Glenn E.]

that seems to have been deliberately created to exclude Pluto.

What is the evidence of this deliberate exclusion? A bright line was found, a logical and natural bright line, and used. Eight things lay on one side of it, not nine. That’s not deliberate exclusion.

IAU: "(1) A "planet"1 is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit."

Random Astrophysicist: "Uh... you do realize that the Earth is no longer a planet if you use that definition, right?"

IAU: "Oh crap! Um... I know, let's change it to say '(c) dominates the neighborhood around its orbit.' There! All fixed!"

Random Astrophysicist: "..."

[jdaw1]

Does cleared mean cleared like I clear the kitchen (earth has massively out-performed), or like my mother-in-law does (it’s a tie)?

[Glenn E.]

Does cleared mean cleared like I clear the kitchen (earth has massively out-performed), or like my mother-in-law does (it’s a tie)?

One must assume that since the IAU felt the need to clarify their definition from "cleared" to "dominated" that Mars, Earth, Jupiter, Neptune, and Pluto have all not "cleared" their orbits.

And for the record, I do not accept this as a given:

With the discovery of lots of large-ish KBOs, a definition was needed.

Why? Why does the discovery of lots of large-ish KBOs prompt a need for a new definition? Can they not be studied unless we know whether or not they are planets? Would the be studied differently if they were, say, comets or mere asteroids?

[jdaw1]

the IAU felt the need to clarify their definition from "cleared" to "dominated"

That was me, not the IAU. By cleared the IAU seems to mean that it is at least a dozen times chunkier than all other things in that orbit.

Why? Why does the discovery of lots of large-ish KBOs prompt a need for a new definition? Can they not be studied unless we know whether or not they are planets? Would the be studied differently if they were, say, comets or mere asteroids?

Because, I guess, folks asked whether they were planets, and the initial response — “vell, you know, planets are just these planety things” — was somehow thought unsatisfactory. So they wanted a bright-line as-clear-as-possible as-natural-as-possible definition. They didn’t start with “This is our chance to knife that Pluto thing in the back”; they started with a hunt for a seemingly natural definition.

IIRC, the original Stern–Levison paper used different words. It called ‘unterplanets’ things that the IAU calls dwarf planets; it called ‘überplanets’ things that the IAU calls planets. Same bright line; different labels.

[Glenn E.]

the IAU felt the need to clarify their definition from "cleared" to "dominated"

That was me, not the IAU. By cleared the IAU seems to mean that it is at least a dozen times chunkier than all other things in that orbit.

I believe I've seen that distinction being made prior to this conversation, so no I don't think it's just you.

Why? Why does the discovery of lots of large-ish KBOs prompt a need for a new definition? Can they not be studied unless we know whether or not they are planets? Would the be studied differently if they were, say, comets or mere asteroids?

Because, I guess, folks asked whether they were planets, and the initial response — “vell, you know, planets are just these planety things” — was somehow thought unsatisfactory. So they wanted a bright-line as-clear-as-possible as-natural-as-possible definition. They didn’t start with “This is our chance to knife that Pluto thing in the back”; they started with a hunt for a seemingly natural definition.

They're KBOs. Pluto happens to be a KBO that we also call a planet. Eris is a scattered disk object; we haven't decided whether or not to call it a planet yet. Planet has no scientific meaning; it's just a label.

Aside: still haven't answer the question of what we're supposed to call all those objects orbiting other stars. Can't call them planets anymore because the IAU screwed up the definition, as often happens when doing something that really isn't necessary.

IIRC, the original Stern–Levison paper used different words. It called ‘planets’ things that the IAU calls dwarf planets; it called ‘Über-Planets’ things that the IAU calls planets. Same bright line; different labels.

Unterplanets and Überplanets.

Personally, I'd have left "planet" as a broad category that includes them all, with 8 "major" planets and a few (at that time) "minor" planets.

Win-win. Pluto is still a planet, but it, Eris, Ceres, Haumea, Makemake, etc can be distinguished by the Stern-Levison Parameter for those who care.

[jdaw1]

Planet → Major planet;
Dwarf planet → Minor planet.

That would have worked excellent for me. It maintains the physically meaningful Stern–Levison distinction, and keeps you happy. Win-win.

[DRT]

Hurray!!

Does that mean Pluto is a planet again?

How are we going to break the news to the world?

[Glenn E.]

Planet → Major planet;
Dwarf planet → Minor planet.

That would have worked excellent for me. It maintains the physically meaningful Stern–Levison distinction, and keeps you happy. Win-win.

Yes. My problem with the IAU's decision is multifold, but one component is that a "dwarf planet" is not considered a sub-class of a "planet." With the original Stern-Levison distinction, they were all still "planets" with further sub-classes.

I think it is also notable that Stern himself does not support the IAU's definition.

[jdaw1]

The problem has shifted. It seemed previously to be the reasoning and formula behind the distinction. Whereas I thought the bright line to be in a well-judged place. Now it seems the problem is with the chosen names. Fine: names schmames.

[LGTrotter]

Glenn is right. Particularly as he has the astronomical correspondent on side.

But please, carry on.

[DRT]

The problem has shifted. It seemed previously to be the reasoning and formula behind the distinction. Whereas I thought the bright line to be in a well-judged place. Now it seems the problem is with the chosen names. Fine: names schmames.

I think you are completely missing the point of Glenn's argument. There is no need for a line, bright or otherwise.

Someone decided to draw a line and then convinced some people that the line had meaning. Now people worship the line and believe it to be true whilst others think it to be just an invention that suits the needs of the inventor and his followers.

This is not the first time this has happened, but that doesn't make the invention necessary.

Question: ignoring their distances from the Sun and relative differences in the vastness of their orbits, does Pluto have more in common with Mercury than it does with Jupiter?

[jdaw1]

Question: ignoring their distances from the Sun and relative differences in the vastness of their orbits, does Pluto have more in common with Mercury than it does with Jupiter?

Why ignore that manifest and long-lived fact?

[Glenn E.]

The problem has shifted.

Not really. I have simply revealed yet another aspect of the problem. I still have problems with the formula, as well, such as the fact that it includes distance from the Sun. This means that there could be a Jupiter-sized ball of rock somewhere out there that would be considered a dwarf planet. Jupiter. A dwarf. Right.

The elephant is still in the room. According to the IAU, what do we call objects that orbit other stars? We keep discovering them. If it's so important to be able to refer to objects in the Kuiper Belt correctly, surely it is also important to be able to refer to objects orbiting other stars correctly, too.

And this is the actual crux of the issue. The entire thing came up because of arguments about what to name newly discovered objects. The IAU has naming conventions for newly discovered objects, and it is apparently critically important that we only name objects after the appropriate IAU-designated mythological group. Otherwise the universe will implode. Or aliens won't be able to find our address. Or something.

This required a vote of 9000+ astronomers? (Of which reportedly on 424 actually voted?)

[jdaw1]

This means that there could be a Jupiter-sized ball of rock somewhere out there that would be considered a dwarf planet. Jupiter. A dwarf. Right.

Correct. If Jupiter were more than 98 light years from the sun (yes, that far) it would indeed be a dwarf planet. Except that such a Jupiter would be outside the sun’s Hill radius, and so not in orbit around the sun at all. Obviously Jupiter’s cutoff distance is largest, but even Uranus would need to be ≥102,000 A.U. from the sun, so, again, outside the sun’s Hill radius. For a lump of rocky as piddly as the Earth the cutoff is 2,870 AU, which is still not small.

The elephant is still in the room. According to the IAU, what do we call objects that orbit other stars? We keep discovering them. If it's so important to be able to refer to objects in the Kuiper Belt correctly, surely it is also important to be able to refer to objects orbiting other stars correctly, too.

Entirely agree. Needs doing. same definition — albeit different words — please. Major, minor. Except that we can’t yet detect mid-size ‘planets’.

Otherwise the universe will implode. Or aliens won't be able to find our address. Or something.

If you want a Dark Stuff versus MoND dispute, start a different thread. I like MoND, so want somebody competent to explain why it just ain’t so.

This required a vote of 9000+ astronomers? (Of which reportedly on 424 actually voted?)

Lordy! And now you want me to rant about electoral systems? Really?

[DRT]

Question: ignoring their distances from the Sun and relative differences in the vastness of their orbits, does Pluto have more in common with Mercury than it does with Jupiter?

Why ignore that manifest and long-lived fact?

Because they are irrelevant to what the objects are. All of these objects formed through the coalescence of material orbiting a star. Rather than avoiding the question you could perhaps try to answer it. Which is more like Pluto: Jupiter or Mercury?

[jdaw1]

Because they are irrelevant to what the objects are.

These things are not stationary lumps of rock under a deity’s microscope. Their movement is essential to the not-falling-into-the-sun trick. (Good trick if you can do it. Highly recommended.) The movement is part of what they are, where they are, how they formed, and the rest. So “irrelevant to what the objects are” is, at best, contentious.

[DRT]

I have often found in life that when someone repeatedly avoids answering a direct question it is because they know their argument is built on sand.

So, jumping to the next part of the argument, given that Mercury and Pluto are much more similar objects than either is to Jupiter (and both by an enormous margin), why would one not be a planet just because it is farther away from the Sun and therefore denied the opportunity to "clear its orbit"? It is a distinction that has less meaning the farther away an abject is from the Sun therefore the bright line is arbitrary and not related to the fundamental basis of what these objects actually are.

[DRT]

This required a vote of 9000+ astronomers? (Of which reportedly on 424 actually voted?)

Which gives the argument as much legitimacy and sense as a London Tube strike.

[jdaw1]

Which is more like Pluto: Jupiter or Mercury?

Body	Λ	Log[Λ]	Distance Pluto
Mercury	1.93E+03	3.29	5.82
Jupiter	1.30E+09	9.11	11.64
Pluto	2.95E-03	-2.53	0

So Mercury is more like Pluto than is Jupiter, says the Stern-Levison parameter Λ.

[jdaw1]

This required a vote of 9000+ astronomers? (Of which reportedly on 424 actually voted?)

Which gives the argument as much legitimacy and sense as a London Tube strike.

Different questions. Is the Stern-Levison much more sensible than you Luddites seem to claim? Yes, definitely.

Was the process behind the decision entirely satisfactory? Oh, is that the time? And my glass is empty. Oh! Must deal with these things. {Wipes sweat from brow.}

[jdaw1]

I have often found in life that when someone repeatedly avoids answering a direct question it is because they know their argument is built on sand.

The question explicitly makes an assertion — location irrelevant — which ain’t necessarily so.

So, jumping to the next part of the argument, given that Mercury and Pluto are much more similar objects

Except that the one that is the planet is 25 times chunkier, butt up against the sun and almost tidally locked to it, and has no moons; whereas the non-planet is 25 times less massive and so far from the sun that most things that are gases at Port-drinking temperatures are instead lumps of solid ice, has a moon a very large chunk of its own mass and smaller moons too (this being possible because further from the sun), and has an orbit controlled by a planet named after a watery god.

So, not quite the same. Mostly because of location.

And, while we’re on the Mercury-Pluto comparison, a lump of rock as massive as Mercury but in Pluto’s orbit would be a planet, albeit with not much spare.

[LGTrotter]

'The Sky at Night' has a Pluto special on now for the UK based side of the argument.

[DRT]

Your argument appears to be boiling down to size.

There are many examples in nature where size does not affect the consideration of whether or not two things are from the same class:

Is a Chihuahua a dog even though it might be 100 times less massive than a very large dog?

Is a Bonsai tree a tree?

Is Warwick Davis a person?

Is Ben Nevis a mountain?

Why would size be important to what can be considered a planet? Surely it would make more sense to define what properties a planet should have and then categories objects as planets if they have those properties? Being geologically active and not just a dead lump of rock covered in impact craters seems like a much better test than "small and far away".

I strongly suspect that if the pictures we have seen in the past few days had been available at the time of the vote Pluto would still be a planet.

[DRT]

'The Sky at Night' has a Pluto special on now for the UK based side of the argument.

I just watched it. It didn't change my view but did raise the question of whether or not Charon is also a Planet.