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Your mom's so fat, she pushes the barycenter of the solar system outside of the diameter of the Sun
i mean, with that logic, nothing orbits anything
No, this is actually really relevant. This is part of the logic applied to labeling Pluto a dwarf planet. Pluto and it's moon do this, Earth and our moon do not. Yes, obviously the center of mass of the two isn't the exact center of the earth but it's still within the earth.
Asking a physicist about the center of an object is like asking a Tumblr user about thr color of the sky. The only response will be "which one?" And a sigh of exhaustion
Center of volume ≠ center of mass ≠ center of systemic gravity ≠ center of lift…
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You're not wrong. Everything orbits the center of mass of the system, meaning the mass of the star and the body in orbit. And that is handy for astronomers, many exoplanets have been found using the Doppler spectroscopy method. Doppler spectroscopy measures the Doppler shift in the star's light as it is pulled towards and away from us by planets in orbit. The newest spectrographs are sensitive enough to detect a star's wobble caused by an Earth sized body in orbit. The barycenter is still within the star, but not at the center of the star's mass.
Fun fact: You actually pull the Earth up with the same force it pulls you down.. Newton’s Third Law.
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In a field of study where it’s not just acceptable, but prudent to round pi to “1” because the numbers are that big….
I gotta say, it’s close enough to say Jupiter orbits Sol. Just saying.
Nah, there is no way any astronomer studying orbital mechanics in our solar system is rounding pi to 1. There is virtually no practical calculation you could do on the mechanics of the sun or planets where rounding a known constant by a factor of 3 would yield any useful result whatsoever.
Rounding pi to 1 only makes sense when the uncertainty in the numbers is large, not the magnitude of the numbers, and we know the masses and distances of the objects in our solar system to an amazing level of precision!
Plus, the fact that Jupiter is massive enough to actually exert an influence that large on the sun is pretty fucking cool!
The reason being, that once you go large enough, a multiplier of three is irrelevant, and they only really care about orders of magnitude. You might be tempted to argue that that doesn't happen inside the solar system, and you'd be right. Mostly.
Except that astronomy doesn't concern itself with just our system. So yes. Astronomers do frequently round to 1 because it really doesn't matter that much in the scheme of things. (particularly talking about distances.) it's even more so for cosmology.
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Is it more true to say that Jupiter (and the other planets and asteroid belts and dust clouds in our solar system) orbits the Sun, and the Sun orbits the barycenter? The barycenter that the sun revolves around is influenced (marginally) by the other bodies in the solar system and not just Jupiter. If the definition of a barycenter is to be interpreted as this image suggests, that would mean that no material object orbits another material object and they instead orbit their collective center of mass somewhere in space.
Edit: to clarify, I understand the physics and motion at play. The phrasing just seems misleading/incorrect to me.
no material object orbits another material object and they instead orbit their collective center of mass somewhere in space.
That’s exactly what happens. Why do you think this is incorrect?
It seems to fundamentally change what it means “to orbit” something.
As I understood the term, orbiting would be used correctly in these cases:
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A lighter object orbits a heavier object, and both of their paths of motion are elliptical about their barycenter
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Two objects of identical mass orbit each other, and their paths of motion are circular about their barycenter
In contrast, the image above implies the following:
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A lighter object does not orbit a heavier object; they both orbit their barycenter with an elliptical path of motion
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Two objects of identical mass do not orbit each other; they both orbit their barycenter with a circular path of motion
Even the Wikipedia page for barycenter, which OP linked to, opens with the following:
“the barycenter… is the center of mass of two or more bodies that orbit one another and is the point about which the bodies orbit.”
Perhaps “orbit” as a verb has two meanings, depending on the specificity of the context.
I guess your conclusion is right. In situations where the barycenter of two (or more) objects is not sufficiently different from the center of mass of the heaviest object, we simplify the description by assuming that the barycenter and the center of mass of the heavier object are equal.
Just because I’ve already edited it, here’s an animation of Earth orbiting the Earth–Moon barycenter:
No, your earlier definitions are incorrect. All orbits happen around the barycenter. The only question is whether one of the bodies is large/massive enough that the barycenter is located within it
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I found it super helpful to have the Sun's center of mass labeled!
I only wish Jupiter's center of mass was also labeled in this graphic. I've been trying to puzzle it out myself, but I'm stumped!
I think if it's to scale, Jupiter is way offscreen, like in another room in your building far away.
Do all the planets also orbit around that same barycenter, or does each planet have a different one?
I guess they all orbit around the solar system's center of mass (negligibly affected by the universal CoM), but that CoM probably moves around as the planets themselves move.
Relative to what, you might ask? That depends who you're asking 😉
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Jupiter is so massive, if you give it more hydrogen, it gets smaller.
My dumb friend wants to know why adding more mass would make Jupiter smaller, can you help explain it to him?
I misrembered, it remains roughly the same volume, until 1.6 juipiters of mass, at which point the effect of gravity from each additional hydrogen is greater than the intermolecular forces and additional hydrogen would cause it to compress more than it would grow.
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The increased mass increases the force of gravity on the outer particles which ends up reducing the radius more than the increase due to the layer of new hydrogen, IIRC.
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Fun fact: if I threw a rock hard enough, it and the sun would orbit around their "barycenter" which would happen to be just about the center of the sun (probably, i dont work here).
That’s why I lose my balance!
this post was submitted on 03 Sep 2025
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