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Forum » SpaceEngine » Science and Astronomy Discussions » Science and Astronomy Questions
Science and Astronomy Questions
RockoRocksDate: Monday, 31.03.2014, 17:24 | Message # 241
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Quote Laine115 ()
Why are galaxies flat instead of being spherical?

If you are talking about spiral galaxies there is no such thing, spiral galaxies are always "flat".
The thought that spiral galaxies are spherical is a common misconception.
Just look at this picture of the NGC 891 galaxy, which we see from it's side (it's 'flat')

If we were looking at this galaxy from it's top, it would appear round.
Unless you mean ellptical galaxies like Messier 87, which are indeed spherical to ovoid.





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Edited by RockoRocks - Monday, 31.03.2014, 17:25
 
Laine115Date: Monday, 31.03.2014, 17:36 | Message # 242
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Quote RockoRocks ()
If you are talking about spiral galaxies there is no such thing, spiral galaxies are always "flat".

I know that they are always flat, but my question was why are they flat.





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SalvoDate: Monday, 31.03.2014, 18:54 | Message # 243
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This video explains it very well!






The universe is not required to be in perfect harmony with human ambition.

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(still don't know why everyone is doing this...)
 
johnson_linDate: Thursday, 03.04.2014, 06:27 | Message # 244
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Something just struck to my mind, and it can be completely noob to ask:

The Universe itself is a time machine, because everything we observe is in the past, and the further we see the earlier it gets. So how do we know what we observe actually looks like that, when seeing from a seemingly all-knowing point of view?

Let's say in Space Engine, we look up from a planet, and see some distant stars in the containing galaxy. Then you press "Go to" and get there. But in fact you shouldn't be able to get there, as there should be nothing or have something totally different, because what you see on the original point of view is something from the past, like tens of thousands years ago.

And the galaxy illustration we see everyday, or the universe structures we are told -- are in fact inaccurate (or at least we should say, have different significance of time-lag relative to the distance you map).

How do we deal with this? Or because of the fact that information can't travel faster than light, so it won't matter in any way, anyway.







Edited by johnson_lin - Thursday, 03.04.2014, 06:28
 
SpaceEngineerDate: Thursday, 03.04.2014, 10:24 | Message # 245
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We can't do anything with it, unless we build a warp drive or tachyon telescope.
SE don't model light travel delay for now. In future versions this may be implemented.





 
neutronium76Date: Thursday, 03.04.2014, 10:53 | Message # 246
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Quote johnson_lin ()
Something just struck to my mind, and it can be completely noob to ask:
The Universe itself is a time machine, because everything we observe is in the past, and the further we see the earlier it gets. So how do we know what we observe actually looks like that, when seeing from a seemingly all-knowing point of view?


Our galaxy has a dimaeter of around 100k lys. Within that time frame the changes involved are pretty small: A few thousand stars have gone nova (and similarly some new ones have formed that we don't yet see because light hasn't reached us yet), some nebulae have probably different shape or don't exist at all but in general the galaxy looks pretty much very similar to our current observation. At larger distances, the details we see from our position are less visible so even if we go there magically we would see things that we couldn't see fro here anyway.

Quote RockoRocks ()
Unless you mean ellptical galaxies like Messier 87, which are indeed spherical to ovoid.


Why these galaxies end up being spherical? Also why globular clusters are globular and not flat? Similarly why irregular galaxies are irregular? Why not all structures in the universe end up flat?





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johnson_linDate: Thursday, 03.04.2014, 11:19 | Message # 247
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Thanks for answering SpaceEngineer & neutronium76

So can I say that because the rotation period for, say, Milky Way, is like tens of millions of years, so the time delay would be too small to cause any noticeable discrepancies between our understanding of the galaxy and what is "actually happening"?

But what about on an even larger scale? It's not just what we see or what we can't see. Isn't there any possibility that our understanding of the structures can be wrong, because of the time delay?

Or it's like, the effect of any kind of transition of energy and information can't be faster than light (e.g the effect of gravity or the energy of light itself), so it probably won't matter anyway?





 
neutronium76Date: Monday, 07.04.2014, 08:20 | Message # 248
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Quote johnson_lin ()

Or it's like, the effect of any kind of transition of energy and information can't be faster than light (e.g the effect of gravity or the energy of light itself), so it probably won't matter anyway?


Probably this and also the fact that the rest of the matter (matter that is travleeing at much lower speeds than the speed of light because it is clumped in larger structures e.g gas clouds in a nebula, planets, stars etc..) doesn't change its position too much during large amounts of time, so even at very large distances the structures don't change much. They change in appearance - yes. But too much - No.

Added (07.04.2014, 11:20)
---------------------------------------------
I recently watched this documentary, regarding planets and planet formation and evolution:

and I have a couple of questions:

1. Why Venus has a thick atmosphere despite a) having no magnetic field and b) being closer to the sun while Mars doesn't. (The fact that it is larger i.e. heavier than Mars and hence has a stronger gravity shouldn't compensate IMO)
2. Why our solar system has rocky planets in its interior orbits and gas/ice giants in its outer, whereas other stars have been found to have gas giants orbiting at very close distances to their parent star? It seams that heat is not the only/main reason to prevent gas giant's from forming close to a star. After all gas giants are failed stars so they have their own internal heat. Also the fact that discovered exolpanetary gas giants are many orders of magnitude larger than jupiter and are probably closer to brown dwarf classification.
3. Why only Saturn has wide ring structure, while Jupiter, which is more massive, has only very pale/weak ring structure. I mean, according to the documentary, Saturn rings were formed when Saturn's immense gravity ripped apart a moon that was orbiting nearby. If that was true than wouldn't Jupiter's gravity be strong enough to rip apart Io or the closer small moons (amalthea group)? I believe that Saturn's rings were formed when one moon that was orbiting in that distance, was hit by a comet/asteroid or two moons collided.
4. Saturn's Magnetic field looks light blue in the video whereas in the photos that Harb posted in Saturn's system thread, it looks reddish.
5. The core of gas giants is presumed to be metallic hydrogen which is a conductive and hence generates the gas giant's immense magnetic field. The core of a star is also composed of hydrogen but that hydrogen is converted to helium via fusion which generates the heat and light of the star. In what state is this H? I mean a star has also a very powerful magnetic field so its core must be conductive in some way.




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SalvoDate: Monday, 07.04.2014, 15:31 | Message # 249
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Ok guys, I have some questions for you, hope you can aswer them smile

1. How much a Nebula (like Carina Nebula) could change in something like... 7000 years? (for example, if we could directly teleport there)

2. Can a tidal locked planet have plate tectonics? (and so even mountains or other structures)






The universe is not required to be in perfect harmony with human ambition.

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(still don't know why everyone is doing this...)


Edited by Salvo - Monday, 07.04.2014, 15:51
 
HarbingerDawnDate: Tuesday, 08.04.2014, 05:47 | Message # 250
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Quote Salvo ()
How much a Nebula (like Carina Nebula) could change in something like... 7000 years?

Locally there might be some changes, but overall the nebula would be mostly unchanged. But of course it depends on the specific nebula.

Quote Salvo ()
Can a tidal locked planet have plate tectonics?

Sure. This depends on convection rather than rotation.

Quote neutronium76 ()
Why Venus has a thick atmosphere despite a) having no magnetic field

Gravity, atmospheric composition, and temperature are more important factors than solar wind exposure.

Quote neutronium76 ()
b) being closer to the sun while Mars doesn't

The two planets have very different histories and very different atmospheres. The atmosphere of Mars has never been nearly as thick as that of Venus. Venus is losing its atmosphere, but it has so much atmosphere that it doesn't make a significant difference. The same was not true for Mars.

Quote neutronium76 ()
The fact that it is larger i.e. heavier than Mars and hence has a stronger gravity shouldn't compensate IMO

But it does. The laws of physics do not care about your opinion or anyone else's.

Quote neutronium76 ()
Why our solar system has rocky planets in its interior orbits and gas/ice giants in its outer, whereas other stars have been found to have gas giants orbiting at very close distances to their parent star?

Perhaps coincidence. Perhaps not. The answer is not known with certainty.

Quote neutronium76 ()
After all gas giants are failed stars

No more so than any other planet type. Even even very small stars are still a hundred times more massive than Jupiter.

Quote neutronium76 ()
they have their own internal heat.

So do all planets.

Quote neutronium76 ()
Why only Saturn has wide ring structure, while Jupiter, which is more massive, has only very pale/weak ring structure.

Mass is not the deciding factor. Each planet has its own unique history, so while rings around gas giants may be common, the nature of those rings will be variable.

Quote neutronium76 ()
Saturn's Magnetic field looks light blue in the video whereas in the photos that Harb posted in Saturn's system thread, it looks reddish.

That's not its magnetic field, that's its aurora. The blue one is a false color ultraviolet image overlayed onto a visible light image. The reddish one is true color.

Quote neutronium76 ()
In what state is this H?

Plasma

Quote neutronium76 ()
I mean a star has also a very powerful magnetic field so its core must be conductive in some way.

Plasma is charged, and moving charged particles create magnetic fields.





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Edited by HarbingerDawn - Tuesday, 08.04.2014, 05:50
 
neutronium76Date: Tuesday, 08.04.2014, 07:23 | Message # 251
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Quote HarbingerDawn ()
But it does


Well then, why earth has only 1atm pressure? It seems that differences in chemical composition in combination with differences in temperature must play a more important role than gravity.





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HarbingerDawnDate: Tuesday, 08.04.2014, 14:26 | Message # 252
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Quote neutronium76 ()
It seems that differences in chemical composition in combination with differences in temperature must play a more important role than gravity.

What I meant was that is what plays the most important role in atmosphere loss. There is no single set of factors which decide how much air a planet has, it varies with each planet's specific history.





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UnnamedDate: Sunday, 20.04.2014, 05:00 | Message # 253
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Earth has 1 atmo pressure because earth's atmo pressure is 1 unit of atmo pressure
I got a question btw:
1-Why aren't there any O1V or O0V stars?
Is it because they are unstable or something?





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apenpaapDate: Sunday, 20.04.2014, 11:43 | Message # 254
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I think the reason is that they're still saved for potential stars even hotter than O2. When the system was first introduced, it only went up to O5. O4, O3, and O2 have been introduced since, O2 being a class only since 2002.




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HarbingerDawnDate: Thursday, 24.04.2014, 06:11 | Message # 255
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Quote Master_Rambo ()
I'd be really cool if you made super-earths that are 60,000 km in diameter

That's extremely unrealistic. It probably cannot occur in reality.

Quote Master_Rambo ()
I know there are much larger gas giants out there

Only ones that are very hot. From what I know, only a very small number of gas giants that are located far from their stars are larger than Jupiter. Most are Jupiter-sized or smaller. So a limit of 160,000 km (which seems to be the current) might not be ideal, but a limit of 180,000 km would be realistic, with the vast majority being smaller. In fact, the current number of gas giants that are 150,000+ km wide is probably too large.





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