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Forum » SpaceEngine » Science and Astronomy Discussions » Science and Astronomy Questions
Science and Astronomy Questions
HarbingerDawnDate: Tuesday, 27.11.2012, 18:39 | Message # 91
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Quote (smjjames)
I'm just wondering how close (in distance and orbital period) two stars have to be in order to be considered a contact binary?

It depends on the stars. Very dense stars will be able to get very close to each other before coming into contact, whereas a diffuse star will have its photosphere pulled away towards its partner more easily. There is no set distance/period for determining contact binaries, you would need to figure out the equations and run them for every star you encountered to figure out whether they would be or not.





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SpaceEngineerDate: Tuesday, 27.11.2012, 20:00 | Message # 92
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Quote (smjjames)
I'm just wondering how close (in distance and orbital period) two stars have to be in order to be considered a contact binary?


If distance between stars is equal to sum of their radii, they are contact smile In reality it is more complex, because close stars disturb the shape of each other, and rotate around their common center of mass very quickly, this disturbs their shape even more.

And there exists such exotic objects, like two star cores in a mutual envelope.

http://upload.wikimedia.org/wikiped....ova.svg





 
SalvoDate: Thursday, 03.01.2013, 14:16 | Message # 93
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[Merged from another thread]

Could a moon have its own moon?

Do you think it's possible?
What are the conditions for this to happen?





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Edited by Salvo - Thursday, 03.01.2013, 14:19
 
TimDate: Thursday, 03.01.2013, 14:28 | Message # 94
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I believe that in very rare occasions, it's possible, if the moon is far enough from its parent and if it has enough mass. We've been or we are able to put sattelites in orbit around our moon, why would a natural sattellite not be able to do it by coincidence? Or maybe just temporary until the dwarf moon gets caught in the orbit of its grandparent.

Either way, it intrigues me how Pavone wants to place a small "mothership" for his robot hedgehogs in orbit around Phobos within ten to twenty years.
 
HarbingerDawnDate: Thursday, 03.01.2013, 14:46 | Message # 95
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Unless the moon formed in that position (would have to be very rare) then it is extremely unlikely. The Hill sphere of the parent moon would be so small that a capture scenario would be practically impossible (unless it was captured from within that same system, eg., Titan capturing Hyperion). So it could theoretically happen, but it would be a very unlikely occurrence (as we can see in our own system, where there are no such bodies).

Also, I think that astronomy questions should be posted in the astronomy questions thread (I'll merge this one).





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Edited by HarbingerDawn - Thursday, 03.01.2013, 14:50
 
SalvoDate: Thursday, 03.01.2013, 15:22 | Message # 96
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In Space Engine is possible



Mars will get angry if he finds out that I stolen him a moon biggrin

(HarbingerDawn)
I think that astronomy questions should be posted in the astronomy questions thread


Good idea, but you should change the name

Attachments: 0061378.jpg(67Kb)





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Edited by Salvo - Thursday, 03.01.2013, 15:30
 
HarbingerDawnDate: Thursday, 03.01.2013, 15:41 | Message # 97
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(Salvo)
Good idea, but you should change the name

I thought about it, but it seems good enough for now. I figured that most people would understand its purpose.





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SpyroDate: Sunday, 03.02.2013, 02:31 | Message # 98
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Quote
electrmagnrtic

Lol smile
Replying to old posts once agian.





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DisasterpieceDate: Sunday, 03.02.2013, 07:45 | Message # 99
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How do galaxies get their spiral arms? I read something about density waves but that doesn't make sense in a vacuum.




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neutronium76Date: Sunday, 03.02.2013, 11:07 | Message # 100
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From a quick search in google I came into conclusion: We still don't really know. There are some good wiki articles and also this one which is quite old (1998):
http://casa.colorado.edu/~danforth/science/spiral/

Quote (Disasterpiece)
I read something about density waves but that doesn't make sense in a vacuum


Space is not a vacuum. It depends on scales: If you take 1x1x1 mile cube in space it is vacuum. If you take 1x1x1 parsec could be vacuum but not very vacuum. If you take 1x1x1 kiloparsek it is definetely not vacuum wink





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SalvoDate: Sunday, 03.02.2013, 11:32 | Message # 101
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How do galaxies get their spiral arms?


I've always wondered, but you can see a similar effect on water (microgravity):


Or in cyclones...





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HarbingerDawnDate: Monday, 04.02.2013, 00:33 | Message # 102
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you can see a similar effect on water Or in cyclones...

Spiral forms are ubiquitous throughout the cosmos, but with many different unrelated causes.





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WatsisnameDate: Monday, 04.02.2013, 01:28 | Message # 103
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How do galaxies get their spiral arms? I read something about density waves but that doesn't make sense in a vacuum.


As neutronium said, you need to consider the scales involved. At kilo-parsec scales calling space a vacuum isn't a good characterization.

Galactic spiral arms arise because some driver (perhaps the gravitational influence of the central bar, or another galaxy nearby) causes the stars in the disk to orbit in an organized way. They still follow fairly circular paths, but the paths "line up" in such a way that there is an increase of density in some places and a decrease in others. See illustration on wiki page. These regions of increased density lead to the spiral arms.

Now stars pretty much pass right through the density wave as if it's not even there, but molecular gas/dust clouds are very much affected and become compressed, causing new star formation to occur. This explains why we see a lot of bright young blue stars associated with the arms, as they don't live long enough to travel far from their birthplace.

This Hubble image shows really well how the spiral arms lead to a concentration of dust clouds, and the abundance of blue stars along with them. smile





 
SpaceEngineerDate: Monday, 04.02.2013, 16:12 | Message # 104
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They still follow fairly circular paths, but the paths "line up" in such a way that there is an increase of density in some places and a decrease in others. See illustration on wiki page. These regions of increased density lead to the spiral arms.

Note: He means density of stars here.

In science there are a lot of things that have the same names, because they are defined in a similar way. The word "density" may mean not only density of a liquid or a gas (defines as a mass divided by volume), but also [volume] density of stars in the galaxy (defined as a summary mass of stars divided by volume), or [surface] density of a protoplanetary disk (defined as a summary mass of gas divided by a square in the disk's plane). There are a lot of similar words. For example, many people think the term "flat Universe" of "flat space" is incorrect. How can space be flat if it is volumetric right here? So scientists made up weird theories, that make no sense in the real world! In fact, "flat" means Euclidean, i.e. non-curved. So a "flat Universe" means just that space is not curved.

*





 
HarbingerDawnDate: Saturday, 09.03.2013, 10:48 | Message # 105
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Here's a question that I used to wonder about years ago, and which is hard to find an answer for (for obvious reasons). I'm hoping that one of the more learned members of this forum might be able to attempt to answer it.

What is the albedo of the Sun?





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