orbits

[Darnok]

21 minutes ago, cubinator said:

Well, according to the laws of gravity (which have proven themselves to be pretty consistent with what we see in the universe) it shouldn't really change direction. There are plenty of simulations that suggest it will merge with us in a few billion years. If your Duna rocket is on an interplanetary collision trajectory, it's rather unlikely for that to change if you don't do a correction burn, even if you leave it to the last minute, giving it plenty of time to decide to go somewhere else. The same principle applies to your Andromeda argument. Sure, we can't observe where it is today, but we can predict it's motion because we know where it was in the past. 

But we are able to observe and "draw paths" of Andromeda for 50? 100 years? While we are talking about orbits of galaxies which can be really huge. For example https://en.wikipedia.org/wiki/Galactic_year it should be called "day", because it is single turn around galaxy axis, takes 225 to 250 million terrestrial years... so "galactic year" time need for our galaxy to orbit whatever it could orbit should be much greater like orders of magnitude greater. And with our 100 years of precise observations we would see this galactic orbit as straight lines instead of orbits.

Another thing is that we have no idea what physics laws apply on galaxy level objects... that is why we have dark matter and dark energy hypothesis to explain movement of galaxies?

 

PS Simulation is not evidence nor observation it is imaginary world based on things we think we know (believe that are correct), not on things that makes universe work, that makes simulations closer to faith than science.

Edited March 24, 2016 by Darnok

[p1t1o]

4 minutes ago, Darnok said:

PS Simulation is not evidence nor observation it is imaginary world based on things we know, not on thing that makes universe work, that makes simulations closer to faith than science.

 

8 minutes ago, Darnok said:

...based on things we know...

 

They didn't pull those simulations out of thin air. And they are not even supposed to represent a perfect view of physical reality, but our best guess to-date. And our guesses in these kinds of matter *can be shown by observation and evidence to be quite accurate indeed*.

Simulations may not be 100% philosophical-grade *proof*, but they *are* evidence, and they are based on observation.

Though I do agree that life in the scientific world does require a certain degree of faith, but IMO that does not invoke any mystical or metaphysical inconsistencies akin to those that are associated with, say, religion.

[cubinator]

9 minutes ago, Darnok said:

But we are able to observe and "draw paths" of Andromeda for 50? 100 years? While we are talking about orbits of galaxies which can be really huge. For example https://en.wikipedia.org/wiki/Galactic_year it should be called "day", because it is single turn around galaxy axis, takes 225 to 250 million terrestrial years... so "galactic year" time need for our galaxy to orbit whatever it could orbit should be much greater like orders of magnitude greater. And with our 100 years of precise observations we would see this galactic orbit as straight lines instead of orbits.

We don't use the actual movement of the galaxies to see how they're moving; we use the Doppler effect. Light has a longer wavelength when it's moving away from the observer (red shift), and a shorter wavelength when moving towards the observer (blue shift) due to relativity and the speed of light. Most galaxies have a red shift, so they are moving away from us. But Andromeda has a blue shift, so it must be moving towards us. From this, we can hypothesize that our galaxy will merge with Andromeda in a few billion years.

[PB666]

12 hours ago, Xyphos said:

everything is orbiting something, the moon orbits the earth, earth orbits the sun, the sun orbits a black hole, but what does the black hole orbit? and what does that object orbit? and so on, and so fourth....

The galactic black hole is just a small amount of energy in our galaxy, we would orbit pretty much the same if you replace the black hole with an equal amount of energy close to the center of the galaxy, there are galaxies that lack black holes of any signficant size and there are galaxies that have black holes much larger than expected, its a galactic theme but not a necessity.

[KAL 9000]

40 minutes ago, p1t1o said:

Its helpful to remember the basic premise behind the operation of the Total Perspective Vortex^TM, which contains at its heart, a small piece of fairy-cake. As every object in the universe influences, and is influenced by, every other object, a complete picture of the universe can hypothetically be derived from any piece of matter - in this case, some cake.

Unfortunately, any beings not significantly developed enough to appreciate their insignificance in the cosmos go completely insane upon operating the TPV. (P.S. You got that from Hitchhiker's Guide To The Galaxy, didn't you )

[p1t1o]

Just now, KAL 9000 said:

Unfortunately, any beings not significantly developed enough to appreciate their insignificance in the cosmos go completely insane upon operating the TPV. (P.S. You got that from Hitchhiker's Guide To The Galaxy, didn't you )

Hitchhikers what? I based it all off my own work.

JK of course it is from HGTTG 

[wumpus]

12 hours ago, GoSlash27 said:

It breaks down at the Earth orbiting the sun. Beyond that, the solar system is traveling around the supermassive black hole at the center of the galaxy, but it's not "orbiting", at least not due to gravity. Everything in the galaxy revolves about the center at the same angular rate, like a phonograph record (or a CD for you young'uns), They think this is due to the halo of dark matter that surrounds our galaxy.

The galaxy doesn't seem to be orbiting anything at all as far as they can tell.

Best,
-Slashy

That's weird.  I'll have to look into this, as when I first read your post I assumed it was wrong (an independent body traveling around a mass has only a few options: all of which are described by conic sections.  If it is on an ellipse it has to be orbiting).  The kicker is that as Slashy mentioned, orbiting bodies don't travel at the same angular velocity, but by Keplar's laws.

The idea of dark matter acting as irregular clumps of mass is weird enough, the idea of it acting as some sort of rigid body that drags stars along regardless of gravitational forces is something else.  For those wondering, the easiest way to determine the speed of the stars is by measuring the red/blue shift they emit as they burn.  I'd suspect that our understanding of the spectrum the stars emit is a little wonky before I believed that dark matter acted as a rigid body.  I'd also wonder how much time those few physicists who are really good at tensor calculus spend trying to work such things into general relativity ("the ether grabs things and carries it along" sounds like exactly what relativity is supposed to solve).

[fredinno]

17 hours ago, Ksp Slingshooter said:

Moon orbits earth, earth orbits the sun, the sun orbits milky way's black hole, this black hole orbits andromeda's black hole, these orbit within our universe, our universe could be orbiting other universes within our dimension and our dimension could be orbiting other dimensions (my mind blew away ).

THE MILTY WAY DOES NOT ORBIT ANDROMEDA

6 hours ago, p1t1o said:

Its helpful to remember the basic premise behind the operation of the Total Perspective Vortex^TM, which contains at its heart, a small piece of fairy-cake. As every object in the universe influences, and is influenced by, every other object, a complete picture of the universe can hypothetically be derived from any piece of matter - in this case, some cake.

I don't get it....

[Ksp Slingshooter]

18 hours ago, Aloriel said:

I am not sure about the Andromeda orbit that Slingshooter proposes.

I was just kiding when I said that our galaxie's super massive black hole orbits the one from Andromeda galaxie and so on, because bodies that interact gravitionally outside their SOI's aren't actually orbits.

1 hour ago, fredinno said:

THE MILTY WAY DOES NOT ORBIT ANDROMEDA

I don't get it....

I was just kiding

[pincushionman]

5 hours ago, wumpus said:

…The kicker is that as Slashy mentioned, orbiting bodies don't travel at the same angular velocity, but by Keplar's laws…

Not in the case of the galaxy. Keplers laws only apply to isolated systems with concentrated masses, like within a star system. Stars in a galaxy are certainly isolated point masses, but in the large scale it's pretty much a continuous distrubution of mass from edge to edge. So Newtonian (or better yet, GR) explanations are much better models. The star orbits are mostly circular/elliptical (in the large scale), but not Keplerian, and perturbations from neighboring stars are the norm.

As for the OP's question, "objects" orbit "the barycenter of the system in question." Every object in the Solar System orbits the SS's center of mass, including the Sun, and mainly because of Jupiter that point isn't actually within the Sun.

Does the rest of the galaxy have an effect? Yes, but at the scale of the solar system that's pretty much just noise. Likewise, the Milky Way is isolated enough it can be modeled by itself. Similarly, the entire Local Group is isolated enough to explain the interactions, especially the smaller galaxies that are clearly bound to the combined mass of Milky Way and Andromeda and are clearly orbiting.

Beyond that scale, objects are still gravitationally bound, but "orbit" stops being so clearly defined and it becomes more that "things get pushed (pulled) around a little" due to the vast distances, timescales, and speeds.

[GoSlash27]

2 hours ago, fredinno said:

 

I don't get it....

fredinno,

 Try removing your peril- proof sunglasses

[fredinno]

23 minutes ago, GoSlash27 said:

fredinno,

 Try removing your peril- proof sunglasses

What's that?

[GoSlash27]

fredinno,

 These are all references to the Hitchhiker's Guide to the Galaxy "trilogy". Kind of a cult classic in nerd circles.

https://en.wikipedia.org/wiki/The_Hitchhiker's_Guide_to_the_Galaxy

Best,
-Slashy

[Aloriel]

1 hour ago, Ksp Slingshooter said:

I was just kiding when I said that our galaxie's super massive black hole orbits the one from Andromeda galaxie and so on, because bodies that interact gravitionally outside their SOI's aren't actually orbits.

I was just kiding

Except that in reality, there are no spheres of influence.

In reality, every particle is gravitationally drawn to every other particle in the entire universe. The catch is that so much of the universe is so completely far away that it has virtually zero effect on us.

In actuality, the Milky Way and Andromeda are headed for each other because they are drawn to each other's gravity. They are non-trivial sources of gravity for one another. However, they aren't orbiting each other (hyperbolic trajectory), and technically could miss depending on how erroneous our calculations are.

As an example of the effects of distant gravity, there is the Great Attractor that is drawing all of the neighboring superclusters towards it. Its effect on us is minuscule, but it exists, and eventually - in probably many trillions of years - will draw our galaxy so closely that it is absorbed into it.

[YNM]

16 hours ago, kerbiloid said:

The Sun revolves around the galaxy center with 200 mln period.
Its (and the Solar System's) appearance took about 50-100 mln years.
Does it mean that the first 100 mln years of its existence (i.e. until the first orbit turn) it had no orbit?

Earth does spiral around the Sun, while the Sun does spiral around the Sag A*, while Sag A* flies its own way.
No same place can be here at all. In any moment of time all this pieces are far away from the point of the Universe where they had been a turn ago.

So, any tracjectory is just a superposition of orbits.

Well, at least in some un-weird reference frame it's going back to the same place. Hyperbolic and parabolic orbits, on the other hand, never returns to the same site in whatever reference frame.

[Bill Phil]

What's even weirder is the cylindrical structure near the center of the Galaxy...

17 hours ago, YNM said:

There're no orbits, there's only trajectory. Trajectories can be said as orbits only when they comes back to nearly the same place, so hyperbolic and parabolic trajectory shouldn't be called orbit at all.

For your question... Hmm, hyperbolic trajectory to Andromeda's SMBH ?

An orbit is defined as a curved path followed around celestial objects.