Technically, Earth Does Not Orbit Around the Sun (2014)

https://www.realclearscience.com/blog/2014/08/technically_the_earth_does_not_orbit_the_sun.html

by gojomo • 7 years ago

256 200 7 years ago

Causality1• 7 years ago

"Everything in the solar system orbits around that point."

Depends on exactly how pedantic you want to be. Technically everything in the solar system orbits the barycenter of the galaxy and intra-system movement is the same type of low-distance high-frequency wobbling the author chose to dismiss with regards to the motion of moons around planets.

tomglynch2• 7 years ago

Does this mean even the sun orbits around that point?

saagarjha2• 7 years ago

Yes.

arendtio• 7 years ago

Are you sure that the neighboring galaxies have no effect and it is just about our galaxy? ;-)

nabla9• 7 years ago

If you get that pedantic you must delve into relativistic center of mass and center-of-momentum frame. The speed of gravity is the speed of light. Sun's gravity affects earth with 8 minute lag.

I'm told that you do the math at that level it's almost the same as in the Newtonian model, which is surprising. I never understood the math but it's related to the fact that changes in stress-energy tensor of matter are continuous. Mass+energy moves gradually from place to place, there are no sudden jumps. Earth accelerates towards point point where the Sun is in future. Not the same point as Newtonian mechanics with instant gravity says it should be, but close enough to hide relativistic effects of gravity most of the time.

fenomas6• 7 years ago

In college I took a great "Philosophy of Physics" class, where on the first day the professor asked everyone to write one page on whether the Earth revolves around the sun, and the final project was another paper on the same topic, so we could see how nuanced a question it was and how our views had evolved over the course.

With that said, I don't think there's any valid answer besides "you can define your terms and points of reference such that it does or doesn't; there's no particular physical reality to the matter".

tempguy9999• 7 years ago

Claiming that "there's no particular physical reality to the matter" I don't understand at all. I can make sense of that to a limited degree as a variation on the saying "all models are wrong..", but you seem to have extended that to say that there is no 'right' possible (ie the 2nd part of that saying, that "...but some models are useful").

A naive reading of what you said suggests eg. no spaceflight is possible because no astronomical (or any...) calculation is reliable. Can you clarify?

jules• 7 years ago

What does it mean for the earth to orbit the sun or vice versa?

aluren• 7 years ago

What they mean is that you may take whatever point in space to be your immobile frame of reference and describe all motion with respect to that point. It happens to be convenient to take the center of the Sun as such a point when doing calculations relevant to the solar system but it's not more 'valid' than literally any other point in the universe. You just have to change the equations a bit.

fenomas6• 7 years ago

What I mean is, if two people disagree about whether the Earth orbits the sun, there aren't any experiments where we'd expect them to predict different results. They're both describing the same physical reality, viewed from different frames of reference.

It's analogous to talking about someone throwing a ball on a train. A person on the train can say the ball moves relative to the train, and someone outside can say the ball and train are both moving relative to the Earth, and a guy in a spaceship can say that all three are actually moving relative to the sun. But choosing one of those claims over the others is purely a matter of convenience or perspective, not of physical reality.

acqq6• 7 years ago

there's no particular physical reality to the matter"

Completely wrong. The physical reality is reflected by calculating Newton‘s formulas, which give the center of mass somewhere inside or very close to the Sun, as the article explains.

misnome• 7 years ago

By that argument we actually orbit the centre of the galaxy, with the sun causing a minor wobble on top of that orbit.

It depends on your frame of reference.

goto113• 7 years ago

An interesting tangent: At the time of Gallielo, the church used the Tychonian model of the solar system.

In the Tychonian model, the earth is the center and the sun revolves around the earth. But the other planets revolve around the sun! You will notice this is practicallty the same model as the Copernican model except for the arbitrary definition of what is "the center".

The only observable difference was the relation to the firmament which in the Tychonian model revolved around the earth but in the Copernican revolves around the sun. If the Copernican model was correct, some parallax to the stars should be observable. Now we know this is not observable due to the distance to the stars, but this was not known at the time.

fjsolwmv2• 7 years ago

It's not arbitrary. The only two choices that work are the real center of gravity, and the observer's position with the real center of gravity orbiting the observer and everything else orbiting the real center of gravity. If Tycho chose Jupiter as the center of the orbits, the planetary orbits would have the same problem of epicycles as the older models.

ndm0002• 7 years ago

An interesting read is On the Revolutions of Heavenly Bodies by Copernicus, even if you just read the introduction. It’s an appeal to the Pope regarding the scientific nature of his conclusions. Regardless, they still excommunicated him years later for going against what was thought the authority of scripture.

simplesleeper2• 7 years ago

this isn't entirely true. At the time of Galileo, Tycho was presenting his model (and was a militant enemy of Galileo). Tycho's model was either used or not depending on more local scientific stances, but it wasn't entirely popular.

baron_harkonnen• 7 years ago

points of reference such that it does or doesn't

It's too bad (but not surprising) that you couldn't have gotten a bit deeper into general relativity where even the idea of "points of reference" gets a lot tricker. Even though there's a lot of pop-science talked about "space time" I find most people don't really grasp how really challenging of an idea it truly is.

Newtonian physics and special relatively are quite happy to imagine one observer looking at another from a particular frame of reference. The classic example is of course watching someone driving while you are in a train. Special relativity seems really crazy at first because you realize the length of the car can change if either of them are going close to the speed of light.

But GR does away with this idea that you can understand the universe at all while sitting on a train. In GR frames of reference only exist locally in infinitesimally small units of space and time and are defined by being simple such that all particles being observed move in straight lines. The big insight of GR is that the question "which 'revolves' around the other" is the wrong question because the only way to understand the universe is in slices of space and time where everything moves straight (well you can't ever get 'everything' straight, so even then you just worry about getting it right for a few particles at time).

In GR when you jump forward and land on the ground in front of you, you moved in a straight line the entire time. This sounds impossible because we can't imagine a single frame of reference where we could observe this. And that's what makes GR so hard to understand because the jump forward can only be understood by looking at the way those infinitesimal local reference frames change, but there is no general frame of reference that we can find where we can clearly observe this. In the exact same way that calculus understands a curved line as an infinite sequence of perfectly straight lines, GR understands curved space time as an infinite sequence of perfectly straight frames of reference.

It is, in fact, much more complex than the simple case of trying to understand who is right from the two reports of two observers seeing each other on passing trains.

memling• 7 years ago

In college I took a great "Philosophy of Physics" class, where on the first day the professor asked everyone to write one page on whether the Earth revolves around the sun, and the final project was another paper on the same topic, so we could see how nuanced a question it was and how our views had evolved over the course.

A lengthy and enjoyable read of the original controversy is "The Great Ptolemaic Smackdown."[1] (I prefer to start there, as it's easy to tell whether you are interested in reading after the first few paragraphs, but he did put a ToC together, too.[2])

[1] https://tofspot.blogspot.com/2013/08/the-great-ptolemaic-sma...

[2] https://tofspot.blogspot.com/2013/10/the-great-ptolemaic-sma...

dahart• 7 years ago

With that said, I don't think there's any valid answer besides "you can define your terms and points of reference such that it does or doesn't; there's no particular physical reality to the matter".

Isn’t the article linked here exactly the correct and valid answer of whether the earth orbits the sun? Philosophy likes to make things all seem like perception and mental frame of reference, and sometimes it is with people, but the earth’s trajectory relative to the sun doesn’t change if we think about it different or define terms differently.

Maybe the whole problem is asking an invalid binary right/wrong question, when the actual valid answer is that it’s not binary. This one hinges on your definition of “orbit”, when the real valid answer is that there are more than 2 masses, so using orbit in the first place is misleading. Another valid answer to whether the earth orbits the sun might be 99.87% yes and 0.013% no.

fenomas6• 7 years ago

Philosophy likes to make things all seem like perception and mental frame of reference, and sometimes it is with people, but the earth’s trajectory relative to the sun doesn’t change if we think about it different or define terms differently.

That's exactly the point here - answering the question of which revolves around what boils down to deciding which body is stationary, and that depends entirely on your frame of reference. Viewed from the Earth the sun is moving, and viewed from the sun the Earth is moving, and viewed from somewhere else they both move relative to one another. But none of those viewpoints is any more physically real than the others - they're just choices for where to put the origin of the coordinate system, as it were.

That is, if you wanted to predict how the planets will move in the future, you could start from any of those assumptions and still make correct predictions. That's what I mean by saying there's no physical reality to the matter of which frame of reference you choose.

bardworx2• 7 years ago

Isn’t the article linked here exactly the correct and valid answer of whether the earth orbits the sun?

Is it though? I'm genuinely curious. For example, in our current reference, earth almost always is orbiting the sun, but what would happen if the entire system was not contained in the galaxy but in the middle of space (not attached to any galaxy), how would the planetary orbit change?

Another question would be if our solar system was closer to the center of the galaxy, would the orbits of the planets stay the same or would they be skewed because of gravitational forces from the center of galaxy + other solar systems?

Another valid answer to whether the earth orbits the sun might be 99.87% yes and 0.013% no.

I'm not sure if you're an astronomer or have a weather of knowledge or PhD in this topic but from the article, the answer is given as "Technically, what is going on is that the Earth, Sun and all the planets are orbiting around the center of mass of the solar system," writes Cathy Jordan, a Cornell University Ask an Astronomer contributor." That would be the only correct answer it seems. If the center of mass happens to be direct center of the sun or skewed one way or other is irrelevant to the fact. However, I could be wrong in my understanding.

AlEinstein• 7 years ago

If one is going to play the “well technically“ game then we need to describe the motion with relativistic physics rather than Newtonian physics.

taneq• 7 years ago

Also you can't just treat the solar system as a point mass if you're inside it. Earth does orbit the sun but it is also perturbed to some degree by every other mass in the universe.

zeofig• 7 years ago

An annoying and tedious game, played often by physicists...

stabbles• 7 years ago

In a 2-body system on the complex plane, can't you basically take any point as the origin and describe the motion of te bodies in terms of a complex Fourier series, with the interpretation that the bodies orbit a circle on a circle ... on a circle ... around your chosen point?

Edit: Basically Ptolomy did that the 2nd century AD.

layoutIfNeeded• 7 years ago

The word you’re looking for is: epicycles

tomglynch2• 7 years ago

"Everything in the solar system orbits around that point."

Does this mean even the sun orbits around that point?

ah27182• 7 years ago

Yep. Thats the cool thing about the center of mass: its always the center of rotation for a set of moving bodies.

pbhjpbhj• 7 years ago

Of course the point isn't a point, the solar system is moving relative to the galactic centre, which is moving relative to other galaxies. And space itself is changing.

So as, pointed out elsewhere, we choose our points of reference and they're pretty arbitrary when you consider the whole Universe.

praptak2• 7 years ago

The Moon also revolves around the center of mass of the solar system. In a sense more than it does around the earth. In particular Moon's orbit around the barycenter is convex - the popular picture of Moon's orbit having loops is wrong in that sense.

rocqua2• 7 years ago

the popular picture of Moon's orbit having loops is wrong in that sense.

Do you mean the moon never moves 'backwards'?

betenoire• 7 years ago

https://qph.fs.quoracdn.net/main-qimg-c8ca8c109ecb9dacdaa829...

Something like this

jpindar• 7 years ago

Yep. Here's a discussion with diagrams and numbers: https://astronomy.stackexchange.com/questions/10979/moons-or...

praptak2• 7 years ago

It never goes backwards and it never "bends in" towards Sun.

mncharity• 7 years ago

My illustrative story from a few years back, was that if Earth were to vanish, the Moon's orbit would merely smooth out a bit, losing a slight ripple. Whereas if Jupiter were to vanish, Io would zoom away, perhaps even leaving the solar system, or impacting the Sun.

vortico• 7 years ago

I don't know what definition of "orbit" the author is using, but what he explains is how scientists define it.

puzzledobserver• 7 years ago

I was actually surprised that if all the planets were lined up, the center of mass would be outside the surface of the Sun. I had always assumed that the Sun was so massive that the center of mass was almost fixed and certainly always within its surface. I guess I hadn't factored in the fact that the planets are so far away and the Sun so small that their masses could have such large measurable outcomes on the center of mass of the system.

thret• 7 years ago

Well, 'the Sun so small' is a phrase I have never seen before.

toyg• 7 years ago

There is always something bigger, isn’t it...

maxnoe• 7 years ago

No? Never saw videos like this one? https://youtu.be/i93Z7zljQ7I

LifeLiverTransp5• 7 years ago

I wonder wether this center of mass moving around in the sun, is producing - time delayed of course- the "sun-weather" aka, the dark spots and solarflares..

Something else:

Technical the orbit, is a spiral of the whole system around the center of mass, slightly deteriorated by remainders of old interactions.

Which got me thinking, if you run a astronomical simulation backwards- can you computate old interactions and "gone" missing bodys from that? Use celestial motion as a sort of archive-trail to go back along?

ses1984• 7 years ago

I think our ability to look backwards is limited by the precision of our instruments and the precision of floating point computation.

Any error in our measurements would be magnified as we look backwards to the point that the simulation would at some point significantly diverge from reality, I wonder how many years back you can look before that happens?

Also floating point error would compound on top of that.

TheAdamist• 7 years ago

This idea about solar weather affected by the planets was just in the news

https://www.sciencealert.com/the-sun-s-11-year-cycle-have-ma...

ghthor2• 7 years ago

I've had very similar thoughts concerning coronal hole locations on the suns surface. I've also wondered too if the 11 year sunspot cycle is related to a dark mass orbiting the sun, or the solar polar field alignment that flip flops a regular intervals.

I'd suggest lurking around the stream of thought and materials coming from Ben Davidson and the Suspicious Observers community if this interests you.

jgtrosh• 7 years ago

Well it is outside the surface right now, no need to imagine all planets being perfectly lined up.

narnianal2• 7 years ago

The center of gravitation is also just a simplification, or how scientists call it: "a model". Actually everything gravitates around everything else, as the article also explains.

Models, or simplifications, aren't bad though. Because what value can you get out of "everything gravitates around everything else"? Not much. But if you use a model, you can use the model to explain what happened in the past and use it to make an approximated assumption about the future. You can use it to guide decisions, and you can use it to focus on more details in other areas. E.g. if you don't use the actual trajectory of everything but a model, you can still calculate where Mars will be when you reach it if you start right now from point X on Earth. Of course the center of Mars will not be at exactly the same point, but it will be a good enough approximation that you can start planning resources required to get there, and it can help you decide if "now" and point X are good inputs to that travel plan.

Models are a good, helpful tool. They are just not explaining everything, and that on purpose, and as a human we always need to be aware of that models are just models and not reality.

azernik• 7 years ago

Because what value can you get out of "everything gravitates around everything else"?

Expensive numerical simulations!

groestl• 7 years ago

Or semi-esotheric bestsellers!

narnianal2• 7 years ago

Simulations with numbers are also models. You can make them indefinitely more complex and still have a model that is only an approximation of reality.

rolltiide2• 7 years ago

Actually everything gravitates around everything else, as the article also explains.

What helped me understand it the most was an answer to this question:

"Where does the Solar System end"

"When the dominant gravitational influence is not the Sun"

it seems like it is always a loaded question because it is relative to the body being talked about and not its own moons, but it really just comes down to gravitational influence.

matt-attack• 7 years ago

Let’s say all the planets’ orbits decayed and ultimately spiraled into the sun. Wouldn’t that be a possible end to the solar system? I mean it’s just be a sun at that point. But I think the Sun would still be the dominant gravitation force.

omazurov• 7 years ago

Models are a good, helpful tool. They are just not explaining everything, and that on purpose, and as a human we always need to be aware of that models are just models and not reality.

Do we have anything else but models?

dotancohen• 7 years ago

It is repeated in all these super-pedantic threads. All models are wrong. Some models are useful.

jaredklewis• 7 years ago

Indeed. As I learned from a link posted to HN the other day, apparently there is a name for this tension between the accuracy and comprehensibility of models: Bonini's paradox.

https://en.wikipedia.org/wiki/Bonini%27s_paradox

edoo• 7 years ago

Since gravitational waves travel at the speed of light there should be a delay as well where the gravity of one body is affecting another from where it was not where it is. For earth that is where the sun was 8 minutes ago. Technically the galaxy might be orbiting something too.

rocqua2• 7 years ago

I recall hearing that another effect in GR compensates for the delay of gravitational waves to make a binary system act according to newton's laws.

gbear6053• 7 years ago

In fact, this is not how it works. My understanding is that whatever the gravitational force is carried by (ie. gravitational waves) is also affected by the velocity and rotational velocity of the gravitating object (in this case, the Sun), so the Earth really is attracted to the Sun’s current position, not where it was 8 minutes ago. Of course, this only works if no net forces are applied to the sun in those eight minutes, but that’s almost definitely the case. I believe, although it’s been a while since I did the calculations, that if this were the case then the galaxy would gradually become funnel shaped before eventually dissipating after the center gets too far away from the rest. It would have similar effects on the solar system as well.

Simon_says3• 7 years ago

current position

Careful there, buddy.

projectramo• 7 years ago

This article will probably single handedly produce several hundred “well, actually” responses on Twitter.

TeMPOraL6• 7 years ago

There's nothing wrong with "well, actually", despite what the silly meme would have us think.

blurbleblurble• 7 years ago

I was looking for another comment expressing that this article is stupid so I wouldn't have to say it myself and get banned

acomjean• 7 years ago

One of my simulation software projects for a class last century was to try and recreate the slight “wobble” stars have from suspected orbiting planet pulling on them.

The simulation proved they could but it took a fairly large planet in a closish orbit.

Planet finding techniques have improved considerably.

One problem I remember having was Setting the initial state so the planets didn’t just slide off my coordinate system with a constant velocity.

TeMPOraL6• 7 years ago

As the saying goes: all models are wrong; some are useful.

toomuchequate2• 7 years ago

By the way, be careful who you tell this to.

The anti-intellectuals will spin this to prove their own points without any understanding of math or physics.

I've seen this happen, and they are very confident, their 'friends' don't know either. When it comes time, will anti-intellectuals trust scientists or their neighbor?

79522• 7 years ago

It doesn't help that model outputs are often put forward as the main reason for doing something. For example with climate change. But often the problem being discussed is more complex than the single dimension that the science based argument relies on. You have to consider ethics, economics, social effects, and a whole host of other disciplines. People intuitively get this.

You have to have an argument that will pursuade the uneducated, poorly informed neighbor first. And often model outputs just don't cut it.

__MatrixMan__5• 7 years ago

I disagree with the need for a warning. I think it would be better if this were _more_ commonly used.

So often debates arrive at a stasis like:

"You're wrong"
"No YOU'RE wrong"

And there they sit, each side certain that the other is an idiot.

The alternative is to admit that both parties are right according to their model, and that both models are wrong (because being right is not what models are for). I think this is better because the "which model is more useful" question sets up a lot more potentially fruitful interaction between opposite sides.

The danger you're referring to only occurs in a setting where science is implicitly authoritative in the first place. If we drop that assumption, science still produces the most useful models, but finding the most useful one for your project becomes less adversarial.

ska2• 7 years ago

“The map is not the territory”

This is a similar sentiment, but perhaps more useful initially in conversation with people who may get hung up on what “model” means. It can also lead to a fruitful analogy as people easily grasp why different kinds of maps are important.

marktani• 7 years ago

What is the meaning of being anti-intellectual and who are these anti-intellectuals you talk about?

abtinf• 7 years ago

That saying is wrong.

Newton’s Laws are absolute in a typical human context. A better model must explain everything covered by newton and more. Discovering that better model doesn’t make newton wrong.

FabHK• 7 years ago

Well, the saying is a model for the relationship between a model and reality. Being a model, it's wrong, but it is useful.

TeMPOraL6• 7 years ago

No, the saying is not wrong here. Newton's Laws are wrong, period. They explain some observational evidence to some degree of accuracy. That they're "absolute in a typical human context" is literally the point of the saying I quoted.

chongli• 7 years ago

No, they're also wrong in a typical human context.

Most people have a phone with GPS these days. GPS would flat-out fail to work entirely without correcting for time dilation effects in the satellites. Newton had no concept of time dilation (nor should he have, given his context).

__MatrixMan__5• 7 years ago

Pointing out that Newton sill isn't wrong doesn't mean he was ever right in the first place. It's simply not about right and wrong.

He spun a good tale about the universe. Later somebody else spun a good tale that was better in at least one way. That's all.

dragonwriter4• 7 years ago

As the saying goes: all models are wrong; some are useful.

It's important to also recognize that everything we believe about the world except raw sensory perception is a model and, ipso facto, wrong, though perhaps useful.

javert8• 7 years ago

The fact that sensory information is limited, does not make it wrong. It's a certain perspective on reality, and we can easily accommodate for that.

For instance, we know that a stick isn't actually bent when it goes into water, even if it looks like it is.

More generally, we have no practical problem dealing with reality using the information given by our senses. It's not a problem in our daily lives and it's not a problem for going to the moon, Mars, creating microprocessors, etc.

Sorry for busting up the "deny knowledge to make room for faith" parade.

tomp2• 7 years ago

Surely you mean "including raw sensory perception" ;)

Anon84• 7 years ago

and some are wronger than others.

trhway• 7 years ago

As the saying goes: all models are wrong; some are useful.

models being wrong/right/useful/etc. is just a model of a relation between a model and [an aspect] of reality [or whatever else] the model is supposedly modeling.

TeMPOraL6• 7 years ago

Sure. It's also very useful.

dwighttk• 7 years ago

Every single object in the solar system, from the gargantuan sun to the tiniest speck, exerts a gravitational pull on everything else.

Actually: in the universe, not just solar system.

nothrabannosir• 7 years ago

Fascinating. Basic physics question: the linked Wikipedia page on barycentre suggests that the further away a planet (in a 1 sun 1 planet system), the further the barycentre is from the centre of the sun. How does that work in the context of the declining force of gravity as a function of distance? I would have thought that the further a planet , the less pull it can exert on the sun. Does gravity not work that way?

https://en.m.wikipedia.org/wiki/Barycenter

afiori3• 7 years ago

The barycenter determines the point around which the system rotates, the intensity determines the speed.

irchans3• 7 years ago

I believe this is false in the sense that Mercury's orbit is more centered about the center of the Sun rather than the barycenter of the solar system (center of mass).

Retra• 7 years ago

The barycenter is a balancing point. If you were trying to balance two objects on the ends of a see-saw, if you move one object farther away, the balance point has to move toward it (you're actually balancing moments of inertia, which are functions of radial distance.)

If your gravitating objects are in an orbit, they also have angular momentum and moments of inertia.

jessaustin• 7 years ago

Think of it like this: if the planet were inside the sun, at the very center, that's where the barycenter would be. If the planet were then to move steadily away from the center of the sun, the barycenter would also move steadily (though more slowly) away from that point. As that planet steadily moves away from the sun, there is no point at which the barycenter will stop and start moving back toward the sun.

__MatrixMan__5• 7 years ago

You're right that a nearer small body pulls the large body with a greater force, but after one full orbit the large body has been pulled rightward just as much as it has been pulled leftward. The missing piece is: for how long is the force exerted before the situation repeats?

A distant small body exerts a smaller force for a longer time, and a nearby one exerts a greater force for a shorter time.

It comes down to how much time and how much force. The law of graviton plus Kepler's third law plus some algebra ought to show that you get a larger circle with a weaker force over a longer time (not an obvious result).

petschge2• 7 years ago

It has less pull, but it orbits slower and therefore has a longer time to pull on the Sun.

irchans3• 7 years ago

You hit upon a very important point.

Suppose that you have a 2 planet system: A sun type star (mass 210^30 kg), an Earth type planet 1 AU from the sun (weight 610^24 kg), and a Jupiter type planet (mass 2*10^27 kg) that is 1000 AU away from the sun.

The distance between the Earth type planet the center of the star could be nearly constant.

The distance between the Earth type planet and the barycenter would not be nearly constant -- it would not "orbit" the barycenter in a circular orbit.

I may be wrong and I would be very happy if someone corrected me.

(Note: I think the barycenter would be about 5 AU from the star!)

lmm• 7 years ago

The planet's pull on the sun and the sun's pull on the planet decline at the same rate (they're both proportional to 1/r^2). So the barycenter will always be the same proportion along the line between their centers of mass.

Merrill• 7 years ago

The sun moves at about 828,000 km/hour around the glactic center. Thus, it moves about 7250 million km each year.

The distance from the earth to the sun is about 150 million km.

Therefore, the earth's "orbit" is actually a very elongated helix.

EForEndeavour• 7 years ago

With respect to the galaxy's frame, sure. With respect to the earth or sun, not so much.

LifeLiverTransp5• 7 years ago

Imagine if you had a really, really fine tuned sensor for gravity, you could move a mass on one side of the system, and detect that move on the other side, communicating with gravity waves.

xgulfie• 7 years ago

You could, but it wouldn't move faster than light anyway.

LifeLiverTransp5• 7 years ago

Yes, but it would behave like a wave. You could make a gravity sonar for planets with it.

fourier_mode• 7 years ago

Isn't the title incorrect? As in: it does orbit around the sun, but the center does not coincide exactly with the center of the sun. Or maybe there are other used definitions of the term "orbit around"?

acjohnson55• 7 years ago

I suppose there's no hard line between a single object being the actual center of orbit and a many-body problem. I think the interesting thing to me is that the barycenter is often far enough from the center of the sun to not be within the sun at all. But that's about it.

kingkawn• 7 years ago

Not technically, only actually

TallGuyShort• 7 years ago

Then technically, nothing orbits any other single thing.

nurettin• 7 years ago

How much, in terms of percent variation, could this be? 1%? 2%? When is it going to become significant?

geoalchimista• 7 years ago

Only someone without basic physics literacy would jump from the fact that "planets revolve around the center of mass of the solar system" to the clickbait conclusion "earth does not orbit around the sun". They missed that approximation is a prerequisite for a scientifically meaningful representation of the real world.

methodover• 7 years ago

I liked it. The clickbaity title leads the reader to learn what a barycenter means.

irchans3• 7 years ago

The article quotes Cathy Jordan,"Technically, what is going on is that the Earth, Sun and all the planets are orbiting around the center of mass of the solar system".

I believe that the statement is a good approximation for the orbits of trans-Neptunian objects or any other orbiting object that is more than 40 AU from the Sun, but I think it is a bad approximation for Mercury, and not a good approximation for the Earth. When I say it's a bad approximation, I mean that it would be more accurate to say "the Earth and Mercury orbit the center of the Sun" than it is to say "the Earth and Mercury orbit the barycenter of the Solar System (center of mass)".

Any comments by someone more qualified that me would be appreciated (I took about 6 courses in physics and 2 courses in astronomy in college and I graduated over 20 years ago).

RickJWagner• 7 years ago

Wow, is that catnip-clickbait for the Flat Earth Society...

lisper2• 7 years ago

All scientific theories are approximations, but some are better approximations than others.

For example: one of the reasons that the flat-earthers get as much traction as they do is that "the earth is flat" is actually a reasonable approximation in some circumstances. "Flat" is actually just a special case of "round" where the radius is infinite. If the distance scale that you are concerned with is small (e.g. the size of your own body) and you don't care about small errors, then infinity is a not-entirely-unreasonable approximation of the radius of the earth.

Of course, this all falls apart as soon as you start to care about anything that is more than a few thousand body-lengths away from you. But it's a mistake to say that the flat-earthers are wrong in any absolute sense. They aren't. They're just using a bad approximation for the realities of modern life.

Unless you're sending a spacecraft to another planet, "the earth orbits around the sun" is a perfectly fine approximation.

zuminator• 7 years ago

But it's a mistake to say that the flat-earthers are wrong in any absolute sense. They aren't.

I'd say they're absolutely wrong in the sense that they make the flawed claim that people who assert that the Earth is an oblate spheroid are absolutely wrong, or worse, are engaged in some kind of conspiracy to hide the truth.

lisper2• 7 years ago

Fair enough. My point is just that the claim that the earth is flat is not entirely indefensible under the right circumstances, and so any proclamation that a particular position is wrong (e.g. "The earth does not orbit the sun") calls for a certain amount of humility and awareness of context.

nocturnial• 7 years ago

Fine, it orbits sagittarius A'*' with some very small wobbles caused by sol.

option• 7 years ago

every person who finished some school should understand that speaking about motion without reference frame is meaningless.

Is such frame is proper to Earth (yeah, go google what proper frame is) then the Sun does revolve around Earth. If the frame is not proper to Earth or Sun then they both rotate around common center of mass which is (relatively) near Sun’s center but does not coincide with it.

kbutler• 7 years ago

Well, actually, it isn't orbiting just around the center of mass of the solar system (solar system barycenter), but that is just one of the two foci of the earth's elliptical orbit. The error is of a similar magnitude as assuming the center of the sun vs barycenter of the solar system.

If you're going to be pedantic, get it right.

This article is a much better technical explanation of the orbit, including both the moving center of mass and the elliptical orbit: https://socratic.org/questions/is-the-sun-directly-in-the-ce...

Oh, and the earth's orbit is also distorted by proximity to other gravitational masses, most notably the moon, but we're not going to be /that/ pedantic.

Side note: the phrase "Well, actually," was banned at my house. Not sure why...

Technically, Earth Does Not Orbit Around the Sun (2014)

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