16 ms·
Technically, Earth Does Not Orbit Around the Sun (2014)
- Causality1 7y 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.
- tomglynch 7y agoDoes this mean even the sun orbits around that point?
- saagarjha 7y agoYes.
- arendtio 7y agoAre you sure that the neighboring galaxies have no effect and it is just about our galaxy? ;-)
- nabla9 7y agoIf 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.
- fenomas 7y agoIn 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 7y agoClaiming 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 7y agoWhat does it mean for the earth to orbit the sun or vice versa?
- aluren 7y agoWhat 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.
- acqq 7y agoNo, they actually dispute the „physical reality“ which is completely wrong: the actual words: “there's no particular physical reality to the matter”
- AlEinstein 7y agoIf one is going to play the “well technically“ game then we need to describe the motion with relativistic physics rather than Newtonian physics.
- stabbles 7y agoIn 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 7y agoThe word you’re looking for is: epicycles
- tomglynch 7y ago> "Everything in the solar system orbits around that point." Does this mean even the sun orbits around that point?
- ah27182 7y agoYep. Thats the cool thing about the center of mass: its always the center of rotation for a set of moving bodies.
- pbhjpbhj 7y agoOf 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.
- praptak 7y agoThe 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.
- rocqua 7y ago> the popular picture of Moon's orbit having loops is wrong in that sense. Do you mean the moon never moves 'backwards'?
- betenoire 7y agohttps://qph.fs.quoracdn.net/main-qimg-c8ca8c109ecb9dacdaa8295c535d2bab.webp https://qph.fs.quoracdn.net/main-qimg-c8ca8c109ecb9dacdaa829... Something like this
- jpindar 7y agoYep. Here's a discussion with diagrams and numbers: https://astronomy.stackexchange.com/questions/10979/moons-orbit-around-the-sun https://astronomy.stackexchange.com/questions/10979/moons-or...
- praptak 7y agoIt never goes backwards and it never "bends in" towards Sun.
- arnarbi 7y agoI think it's better to say it never "bends out" away from the sun, which is a different way to statue that it's orbit around the sun is convex.
- mncharity 7y agoMy 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 7y agoI don't know what definition of "orbit" the author is using, but what he explains is how scientists define it.
- puzzledobserver 7y agoI 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 7y agoWell, 'the Sun so small' is a phrase I have never seen before.
- toyg 7y agoThere is always something bigger, isn’t it...
- TeMPOraL 7y agohttps://en.wikipedia.org/wiki/List_of_largest_stars#/media/File:Star-sizes.jpg https://en.wikipedia.org/wiki/List_of_largest_stars#/media/F...
- maxnoe 7y agoNo? Never saw videos like this one? https://youtu.be/i93Z7zljQ7I https://youtu.be/i93Z7zljQ7I
- LifeLiverTransp 7y agoI 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?
- narnianal 7y agoThe 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 7y ago> Because what value can you get out of "everything gravitates around everything else"? Expensive numerical simulations!
- groestl 7y agoOr semi-esotheric bestsellers!
- narnianal 7y agoSimulations with numbers are also models. You can make them indefinitely more complex and still have a model that is only an approximation of reality.
- wdewind 7y ago> In that Empire, the Art of Cartography attained such Perfection that the map of a single Province occupied the entirety of a City, and the map of the Empire, the entirety of a Province. In time, those Unconscionable Maps no longer satisfied, and the Cartographers Guilds struck a Map of the Empire whose size was that of the Empire, and which coincided point for point with it. The following Generations, who were not so fond of the Study of Cartography as their Forebears had been, saw that that vast map was Useless, and not without some Pitilessness was it, that they delivered it up to the Inclemencies of Sun and Winters. In the Deserts of the West, still today, there are Tattered Ruins of that Map, inhabited by Animals and Beggars; in all the Land there is no other Relic of the Disciplines of Geography. https://en.wikipedia.org/wiki/On_Exactitude_in_Science https://en.wikipedia.org/wiki/On_Exactitude_in_Science
- edoo 7y agoSince 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.
- rocqua 7y agoI 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.
- gbear605 7y agoIn 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_says 7y ago> current position Careful there, buddy.
- gbear605 7y agoOkay, yes, current position is not quite correct, but you can replace each instance of it with “the position of the Sun after the same amount of time as it takes for light to get to the Earth from the Sun, according to an observer that is stationary and on neither,” but that’s a mite clumsy (and still not totally correct, but good enough)
- projectramo 7y agoThis article will probably single handedly produce several hundred “well, actually” responses on Twitter.
- acomjean 7y agoOne 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.
- TeMPOraL 7y agoAs the saying goes: all models are wrong; some are useful.
- toomuchequate 7y agoBy 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?
- 7952 7y agoIt 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.
- toomuchequate 7y ago>You have to have an argument that will pursuade the uneducated, poorly informed neighbor first. An emotional/moral argument will be a coinflip with these people. Will they side with the sad story of X, or the anti-intellectual sad story of Y? I do not know the solution, I've seen others propose everything from hiding difficult to understand topics to calling them 'stupid' infront of their peers, etc... Engaging them with logic and argument makes the problem worse. Would be willing to hear ideas if people have them.
- jacobush 7y agoThere are no shortcuts. You have to meet where they are, find common ground and build trust, both ways. It’s incredibly expensive and hard.
- dwighttk 7y 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 7y agoFascinating. 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 https://en.m.wikipedia.org/wiki/Barycenter
- afiori 7y agoThe barycenter determines the point around which the system rotates, the intensity determines the speed.
- irchans 7y agoI 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).
- afiori 7y agoThat might be, but the real statement would be more like that the solar system rotates around the barycenter of the solar system, for sure the moon revolves "more" around the barycenter of the earth-moon pair than that of the whole solar system.
- Retra 7y agoThe 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 7y agoThink 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.
- Merrill 7y agoThe 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 7y agoWith respect to the galaxy's frame, sure. With respect to the earth or sun, not so much.
- deleted 7y ago[deleted]
- deleted 7y ago[deleted]
- LifeLiverTransp 7y agoImagine 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 7y agoYou could, but it wouldn't move faster than light anyway.
- LifeLiverTransp 7y agoYes, but it would behave like a wave. You could make a gravity sonar for planets with it.
- fourier_mode 7y agoIsn'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 7y agoI 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 7y agoNot technically, only actually
- HocusLocus 7y agoIf you try to win a bar bet with this fact you will get 'physically' beaten. That is what I call the Practical Smart-Ass Test. Unless you're doing it to start a fun fight you know you'll win. Either way it's violence all the way down.
- TallGuyShort 7y agoThen technically, nothing orbits any other single thing.
- mrtweetyhack 7y agoTechnically, the Earth does orbit around the sun and orbits around other objects.
- nurettin 7y agoHow much, in terms of percent variation, could this be? 1%? 2%? When is it going to become significant?
- geoalchimista 7y agoOnly 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 7y agoI liked it. The clickbaity title leads the reader to learn what a barycenter means.
- irchans 7y agoThe 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 7y agoWow, is that catnip-clickbait for the Flat Earth Society...
- lisper 7y agoAll 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 7y 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.
- lisper 7y agoFair 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 7y agoFine, it orbits sagittarius A'*' with some very small wobbles caused by sol.
- option 7y agoevery 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.
- com-mecom 7y agowow
- kbutler 7y agoWell, 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-center-of-earth-s-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...