Movement of the Sun?

[Borodog]

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It is orbiting the center of the galaxy, and the galaxy itself is moving relative to its neighbors.

The earth is of course "along for the ride" - but the galaxy is so wide, and takes so long to orbit, that we don't notice the sun's acceleration unless we look really, really hard for it.

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Is there any work which states the speed of the sun through the galaxy? If so, how is this speed relative to the earth's movement? Thanx.

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I did a back-of-the-envelope calculation using numbers I recall off the top of my head and got the earth's orbital velocity about the sun to be of order 4 times the sun's orbital velocity about the center of the galaxy. YMMV.

Edit to add: 4 times is the maximum; the real number will be less because of the flattened, non-Keplerian velocity profile of the galaxy.

[carlo]

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Someone probably already answered this (IDNRTT), but the Sun orbits the galactic center about once every quarter of a billion years or so, and on its way round bobs up an down throught the DISK. I famously screwed up this very calculation in this very forum because I neglected the mass in the DISK, and "derived" that the period of oscillation was the same as the orbital period, when the correct answer is that the Sun bobs up and down about 7 times each orbit; the truly embarrasing part is that my research involves the simulation of gaseous disks. I can only plead that in my research the mass of the disk is completely negligible compared to the mass of the object it is orbiting. Plus stupidity.

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Thanx, Boro. Please can you clarify the "Disk" for no matter how I consider it the galaxy as if in a flat "Disk" is amazing. Can you expand on this and in particular what is above and below the "Disk"?

[PLOlover]

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Yea, because in the first case they had the bible and all telling them that the Earth was the center of the universe and in the latter case all we have is centuries of observation and mathematical models that have matched those observations. Both seem pretty equal to me...

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learn how to read please. I was responding to the barycenter post above mine. they go round common center of gravity. also there's a frame of reference thing, there's no universal or best frame of reference although that would really only apply for two bodies i guess.

to respond to your post, people ago had authorities telling them revolve aroundearth (not true) (btw, this is not found in the bible it is just church teaching), and today people have authorities telling them revolve around sun (also not true).

my point was people today think they're so much smarter, but they're really not in almost all cases they are thinking exactly the same way.

[madnak]

Well, not really. The sun is orders of magnitude more massive than the earth, so the center of rotation (if we ignore everything else in the solar system/universe) is actually probably inside the sun. Someone correct me if I'm wrong. So the sun moves back and forth, while the earth does rotate the sun. Of course, you could use the earth as your frame of reference, but the whole universe gets complicated that way. The simplest, most intuitive (and therefore by human considerations, most accurate) view is that the earth revolves around the sun.

[Borodog]

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Someone probably already answered this (IDNRTT), but the Sun orbits the galactic center about once every quarter of a billion years or so, and on its way round bobs up an down throught the DISK. I famously screwed up this very calculation in this very forum because I neglected the mass in the DISK, and "derived" that the period of oscillation was the same as the orbital period, when the correct answer is that the Sun bobs up and down about 7 times each orbit; the truly embarrasing part is that my research involves the simulation of gaseous disks. I can only plead that in my research the mass of the disk is completely negligible compared to the mass of the object it is orbiting. Plus stupidity.

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Thanx, Boro. Please can you clarify the "Disk" for no matter how I consider it the galaxy as if in a flat "Disk" is amazing. Can you expand on this and in particular what is above and below the "Disk"?

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The Milky Way galaxy is composed of several general parts. There is a flattened disk of gas, dust and stars where the spiral arms are located, that is mostly in circular orbit around the central bulge. There is a lot more variance in the velocity (in terms of both direction and speed) of the bulge stars than the disk stars, which is why it is bulged in the first place. Then there is a more or less spherical "halo" of old population globular clusters that surrounds the whole she-bang. There is also the infamous "dark matter"; most of the mass of the galaxy cannot be seen, and we can only infer its existence based on the velocity curve of the disk stars, which is far too flat to be accounted for by only the visible matter.

I believe the latest theory is that the Milky Way is actually a barred spiral, in that the bulge is elongated along one axis forming a more or less linear "bar" across the center of the galaxy.

The reason that a galaxy wants to form a disk is that as it condenses out of the pregalactic gas, the volume of gas that eventually became the galaxy has some non-zero net angular momentum. Since angular momentum is conserved under the action of a central force like gravity, as the gas collapses to smaller radii, it rotates at higher speed around an axis whose direction depends upon the net angular momentum of the gas.

[PLOlover]

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The simplest, most intuitive (and therefore by human considerations, most accurate) view is that the earth revolves around the sun.

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you're kinda proving my point. simplest, most intuitive ... not most correct. I mean heck the simplest and most provable is that everyting revolves (not rotates) around the earth because I can go outside and watch stuff in the sky go around.

my point ultimately is that people today parrot the party lline just as they did way back, without real understanding.

I mean, just like they had to introduce things like epicycles to make earth center work, (because you run into trouble if you don't), you have to introduce other stuff into sun center if you want to be real accurate.

I mean, if earth revolves around sun, then jupiter must revolve around sun too, right?

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In the two body problem, each body orbits the common center of gravity (the barycenter). Jupiter is large enough that the Sun actually orbits a point slightly above its own surface. The Earth makes it wobble a tiny amount too (a few hundred kms I think), as do the other planets, but Jupiter's effect probably accounts for >99% of the Sun's wobble.

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uh oh, better get geico.

[madnak]

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you're kinda proving my point. simplest, most intuitive ... not most correct. I mean heck the simplest and most provable is that everyting revolves (not rotates) around the earth because I can go outside and watch stuff in the sky go around.

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It's not the simplest hypothesis that accounts for all the observable data. If the sun revolves around the earth, then explain the other planets and their movements in spatial terms. Not so simple now, is it?

Thousands of years ago, belief that the sun revolves around the earth was probably justified, given the limited information they had at the time. Now that we have more information, it's another story.

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my point ultimately is that people today parrot the party lline just as they did way back, without real understanding.

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Sure, most do. The difference is that there's understanding to be had today. In the past, people merely assumed that the sun revolved the earth, and accepted it due to myth. When someone actually gathered data that suggested otherwise, they were opposed as a result of superstition. The idea that the earth orbits the sun, on the other hand, was the best conclusion based on the data that they had. So the sun belief is "superior" in that sense.

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I mean, just like they had to introduce things like epicycles to make earth center work, (because you run into trouble if you don't), you have to introduce other stuff into sun center if you want to be real accurate.

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Aren't you confusing precision and accuracy?

Most of the statements people make about the world are actually not universally true at a very precise technical level. In fact, many basic statements would require revision from a physicist (including advanced concepts and terms) to be "really" true. I can say "the sky is blue" and be accurate, even if it's a simplification. The truth would be closer to, "due to the refraction of sunlight as it passes through the atmosphere, the wavelengths of light that reach my eye are concentrated around the 470nm part of the spectrum." But is it wrong to say "the sky is blue?"

[PLOlover]

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you're kinda proving my point. simplest, most intuitive ... not most correct. I mean heck the simplest and most provable is that everyting revolves (not rotates) around the earth because I can go outside and watch stuff in the sky go around.



It's not the simplest hypothesis that accounts for all the observable data. If the sun revolves around the earth, then explain the other planets and their movements in spatial terms. Not so simple now, is it?

Thousands of years ago, belief that the sun revolves around the earth was probably justified, given the limited information they had at the time. Now that we have more information, it's another story.

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my point ultimately is that people today parrot the party lline just as they did way back, without real understanding.



Sure, most do. The difference is that there's understanding to be had today. In the past, people merely assumed that the sun revolved the earth, and accepted it due to myth. When someone actually gathered data that suggested otherwise, they were opposed as a result of superstition. The idea that the earth orbits the sun, on the other hand, was the best conclusion based on the data that they had. So the sun belief is "superior" in that sense.

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I mean, just like they had to introduce things like epicycles to make earth center work, (because you run into trouble if you don't), you have to introduce other stuff into sun center if you want to be real accurate.



Aren't you confusing precision and accuracy?

Most of the statements people make about the world are actually not universally true at a very precise technical level. In fact, many basic statements would require revision from a physicist (including advanced concepts and terms) to be "really" true. I can say "the sky is blue" and be accurate, even if it's a simplification. The truth would be closer to, "due to the refraction of sunlight as it passes through the atmosphere, the wavelengths of light that reach my eye are concentrated around the 470nm part of the spectrum." But is it wrong to say "the sky is blue?"

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that was all a prologue to my example: what about jupiter?

[PLOlover]

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Accuracy is the degree of veracity while precision is the degree of reproducibility.

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Aren't you confusing precision and accuracy?

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I'm guessing 85% no, 15% yes, with 10% uncertainty.

[PLOlover]

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But is it wrong to say "the sky is blue?"

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if you're making fun of people who say the sky is aqua it is. ( a little weak I know I'm a guy so I don't know a lot of names for colors, I'm sure there's a lot closer colors than aqua)