# What does the sun orbit around? **URL:** \ **Category:** Factual Questions\ **Created:** [April 11, 2012, 2:13pm UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464 "2012-04-11T14:13:52Z")\ **Posts on this page:** 15\ **Page:** 3
**Author:** ![Anne\_Neville](https://avatars.discourse-cdn.com/v4/letter/a/b9e5f3/32.png) [@Anne\_Neville](https://boards.straightdope.com/u/Anne_Neville)\ **Post date:** [April 25, 2012, 5:44pm UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464/41 "2012-04-25T17:44:08Z")
> [@JBDivmstr](#): > > (bolding mine) > > They won’t? :dubious: > Although I am in no way qualified to dispute your statement, (my) simple logic says that they would. > I mean, in the event of a galactic collision it stands to reason that there are going to be at least a few stars that will meet head on, if for no other reason than their immense gravitational pull. > Or am I missing something? 😕 Yes. You’re missing the scale of the distances between stars in most of the galaxy. The Sagan Planet Walk in Ithaca, NY, is a scale model of the solar system, with distances and sizes of each object represented on the same 1:5,000,000,000 scale. The Sun in this model is 27.8 cm in diameter, a little less than 11 inches. If they were to show the nearest star, Alpha Centauri, on the same scale, it would be somewhere in Hawaii. No kidding. Even if the stars are exerting a gravitational force on each other, they’re just so far apart as compared to their size that they are not likely to collide. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [April 25, 2012, 9:41pm UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464/42 "2012-04-25T21:41:11Z")
I remembered in an earlier thread, someone had calculated a probability of two stars colliding for an Andromeda/milky Way collision. Turns out, [it was me](http://boards.straightdope.com/sdmb/showthread.php?t=628695). Who knew? (The calculation is in Post 22, with some discussion in later posts. I got a 0.16 percent chance, but that’s a very rough number.) ---
**Author:** ![Robot\_Arm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robot_arm/32/18280_2.png) [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)\ **Post date:** [April 25, 2012, 11:31pm UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464/43 "2012-04-25T23:31:40Z")
> [@XT](#): > > IIRC, it take approximately 200 million years to complete an orbit, and is approximately 26000 light years from the center… > [@kferr](#): > > Here’s the [Obligitary Monty Python link](http://www.youtube.com/watch?v=NQu_RRLbVDA) _We’re thirty-thousand light years from galactic central point. We go 'round every two-hundred-million years._ The face that it’s roughly accurate puts that song squarely into the realm of genius. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [April 25, 2012, 11:49pm UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464/44 "2012-04-25T23:49:51Z")
> [@Carl\_Pham](#): > > The frame in which the CMB has zero dipole moment certainly qualifies: all observers will agree on whether or not a particular observer is in that frame – it is therefore unique, and you can define “absolute” velocity as velocity measured in this frame, if you like. Is this true? I thought that two widely separated observers, each measuring a zero dipole moment in the CMB, will have a velocity relative to each other (due to Hubble expansion). Sure, you could define a rest frame that works for a single galaxy, but that’s still not “absolute”. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [April 26, 2012, 12:38am UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464/45 "2012-04-26T00:38:54Z")
What you want is the [Comoving coordinate frame.](https://en.wikipedia.org/wiki/Comoving_distance#Comoving_coordinates). ---
**Author:** ![JBDivmstr](https://avatars.discourse-cdn.com/v4/letter/j/b4bc9f/32.png) [@JBDivmstr](https://boards.straightdope.com/u/JBDivmstr)\ **Post date:** [April 26, 2012, 10:07am UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464/46 "2012-04-26T10:07:57Z")
> [@Anne\_Neville](#): > > Yes. You’re missing the scale of the distances between stars in most of the galaxy. The Sagan Planet Walk in Ithaca, NY, is a scale model of the solar system, with distances and sizes of each object represented on the same 1:5,000,000,000 scale. The Sun in this model is 27.8 cm in diameter, a little less than 11 inches. If they were to show the nearest star, Alpha Centauri, on the same scale, it would be somewhere in Hawaii. No kidding. > > Even if the stars are exerting a gravitational force on each other, they’re just so far apart as compared to their size that _ **they are not likely to collide** _. (bolding mine) I concur with you that it’s _ **very unlikely** _ that two stars will directly collide. Thanks **ZenBeam** , for posting the link to the earlier discussion on the subject. 🙂 The reason I originally posted was because I parsed **dtilque** ’s statement to mean that there was a reason (other than the vast distances involved) that no collision(s) would occur. ---
**Author:** ![Jragon](https://avatars.discourse-cdn.com/v4/letter/j/e19b73/32.png) [@Jragon](https://boards.straightdope.com/u/Jragon)\ **Post date:** [April 26, 2012, 10:42am UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464/47 "2012-04-26T10:42:55Z")
How big is the “orbiting hierarchy” between the sun and the galaxy’s CM? Somebody also said the Sun is orbiting the center of mass of the solar system (which in turn is orbiting the center of mass of the galaxy). So we have Luna-\>Earth-\>Sol-\>Solar System’s CM-\>?..-\>Galaxy CM-\>Local Group CM-\>… How many non-trivial “?” are in there? Is there any formal hierarchy like “group of solar systems”-\>“cluster of solar system groups”-\>“group of clusters” etc in between? The terms themselves I made up, but I hope they kind of illustrate what I’m getting at. ---
**Author:** ![Anne\_Neville](https://avatars.discourse-cdn.com/v4/letter/a/b9e5f3/32.png) [@Anne\_Neville](https://boards.straightdope.com/u/Anne_Neville)\ **Post date:** [April 26, 2012, 12:57pm UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464/48 "2012-04-26T12:57:44Z")
> [@JBDivmstr](#): > > The reason I originally posted was because I parsed **dtilque** ’s statement to mean that there was a reason (other than the vast distances involved) that no collision(s) would occur. **dtilque** didn’t say it _can’t_ happen, only that it _won’t_. An asteroid _could_ fall on my house today. There’s nothing in the laws of physics that says that can’t happen. But I can pretty confidently predict that it won’t happen. > [@Jragon](#): > > Luna-\>Earth-\>Sol-\>Solar System’s CM-\>?..-\>Galaxy CM-\>Local Group CM-\>… Earth is not orbiting the Sun, Earth is orbiting the solar system’s center of mass, as is the Sun. The solar system’s center of mass is close enough to the Sun that saying “the Earth orbits the Sun” isn’t too far off. ---
**Author:** ![Malden\_Capell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/malden_capell/32/5274_2.png) [@Malden\_Capell](https://boards.straightdope.com/u/Malden_Capell)\ **Post date:** [April 26, 2012, 1:48pm UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464/49 "2012-04-26T13:48:14Z")
In the Solar System, Venus orbits in a different direction from the other planets, and Uranus ‘rolls’ on its side as it orbits. Do any stars copy such a thing on a galactic scale? As in, orbiting against the trend or ‘rolling’ around Galactic Central Point? ---
**Author:** ![Anne\_Neville](https://avatars.discourse-cdn.com/v4/letter/a/b9e5f3/32.png) [@Anne\_Neville](https://boards.straightdope.com/u/Anne_Neville)\ **Post date:** [April 26, 2012, 1:53pm UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464/50 "2012-04-26T13:53:14Z")
> [@Malden\_Capell](#): > > In the Solar System, Venus orbits in a different direction from the other planets It _rotates_ on its axis in a different direction from the other planets. It orbits the Sun in the same direction as everything else. > [@](#): > > Do any stars copy such a thing on a galactic scale? As in, orbiting against the trend or ‘rolling’ around Galactic Central Point? The plane in which the planets orbit, called the ecliptic, is tilted at a 60 degree angle to the plane of the galaxy. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 26, 2012, 4:55pm UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464/51 "2012-04-26T16:55:30Z")
There are a few stars that orbit in wild and crazy directions, though. Barnard’s Star, the next closest star after the alpha Centauri system, is a halo star that just happens to be passing through our neighborhood right now, making it the galactic equivalent of a comet. ---
**Author:** ![Anne\_Neville](https://avatars.discourse-cdn.com/v4/letter/a/b9e5f3/32.png) [@Anne\_Neville](https://boards.straightdope.com/u/Anne_Neville)\ **Post date:** [April 26, 2012, 5:04pm UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464/52 "2012-04-26T17:04:06Z")
Every galaxy has a halo component, which includes stars and globular clusters orbiting the center of mass of the galaxy in a spherical distribution (ie, not confined to the disk). In our solar system, there are some moons that orbit their planets retrograde (the other way around from how the planets orbit the Sun). If you were looking at the solar system in such a way that the planets seemed to be going around the Sun counterclockwise, these moons would be going around their planets clockwise. We think these moons were captured into orbit around their planets- they weren’t formed in orbit around the planets, the way the Earth’s moon and most other large moons in the solar system were. Galaxies capture stars and smaller galaxies, too, so there’s no reason to think there wouldn’t be stars orbiting our galaxy the “wrong way”. ---
**Author:** ![Capt\_Kirk](https://avatars.discourse-cdn.com/v4/letter/c/779978/32.png) [@Capt\_Kirk](https://boards.straightdope.com/u/Capt_Kirk)\ **Post date:** [April 26, 2012, 6:54pm UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464/53 "2012-04-26T18:54:10Z")
> [@JBDivmstr](#): > > And on a different note… Whose insurance is going to have to pay for damages? 😛 Obviously Andromeda Galactic Insurance as we obviously have the right of way, look at the crazy angle they are speeding at us from!:smack: ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [April 26, 2012, 7:41pm UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464/54 "2012-04-26T19:41:43Z")
> [@JBDivmstr](#): > > Whose insurance is going to have to pay for damages? 😛 Nobody’s. They’ve got several billion years to find a reason for rescission! 😃 ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [April 27, 2012, 8:28am UTC](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464/55 "2012-04-27T08:28:19Z")
> [@Jragon](#): > > So we have > > Luna-\>Earth-\>Sol-\>Solar System’s CM-\>?..-\>Galaxy CM-\>Local Group CM-\>… > > How many non-trivial “?” are in there? Is there any formal hierarchy like “group of solar systems”-\>“cluster of solar system groups”-\>“group of clusters” etc in between? The terms themselves I made up, but I hope they kind of illustrate what I’m getting at. None. The Sun orbits the center of mass of the Galaxy. Note however that it’s not a simple elliptical orbit, but then you can’t appoximate the Galaxy as a point mass, which is a prerequisite for an elliptical orbit.. The Sun kind of bobs up and down “above” and “below” the plane of the galactic disk. If you plotted the path with respect to that plane, it would look like a sine wave with a period of (I think) about 80 million years. Much less than the orbital period, anyway. You can think of this bobbing motion as something vaguely like an orbit about the galactic disk. While there are star clusters, the Sun is not in one. In general, star clusters are either extremely old (globular clusters, which pre-date the galactic disk) or very young (open or galactic clusters). In general, stars form in clusters, but those evaporate as interactions between the various members eject stars. The Sun left its natal cluster a very long time ago. Globular clusters evaporate too, but they started with many more stars than open clusters do, so they haven’t completely evaporated yet. The stars that are left are orbiting very close to each other compared to stars in the galactic disk. And sometimes they do collide. When they do they form [blue stragglers](http://en.wikipedia.org/wiki/Blue_straggler). **JBDivmstr** Sorry for any confusion I caused. I suppose I should have said “almost certainly won’t collide” or something like that. [Previous page](https://boards.straightdope.com/t/what-does-the-sun-orbit-around/618464.md?page=2)