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Do red giants really look like they do in SpaceEngine?
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| SovereignTripod | Date: Monday, 09.07.2012, 00:07 | Message # 16 |
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Observer
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| All the biggest stars I go to look odd. I don't really know how to explain it, so here are some pictures I took. Betelgeuse: 
VY Canis Majoris:
VV Cep A .
Why do they look like that, instead of something more like Sol? 
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Edited by SovereignTripod - Monday, 09.07.2012, 00:10 |
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| HarbingerDawn | Date: Monday, 09.07.2012, 00:10 | Message # 17 |
 Cosmic Curator
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| Quote (fxmodels) Here is some information that will be helpful: Red Giant stars eventually blow off their outer layers and form planetary nebulae, which look irregular and have glowing tendrils of gas like you see in the nebulae in SpaceEngine, but the gas that is blown off of a star is very transparent and you can clearly see the very round star in the middle.
This is not the basis of the rendering of red giant stars as such. It is based on giant convection cells. This is partly discussed here: http://en.wikipedia.org/wiki/Betelgeuse#Circumstellar_dynamics
See also these animations (on which SpaceEngineer may have based his depiction of red giants): http://www.astro.uu.se/~bf/movie/dst35gm04n26/movie.html
Think about it: a red giant or supergiant star is gigantic compared to its mass, so it has very low density - "flimsy as a soap bubble" as Carl Sagan said. But they are also very energetic and unstable, especially in stars like Betelgeuse (Solar-type red giants would likely be more quiescent on average, but SpaceEngine does not model that at present). It is illogical to assume that all very low density bodies of energetic plasma would be perfectly round, though many may be.
You may be right on average, but there are almost certainly some cases in nature where the stars really do resemble what is shown in SpaceEngine.
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| fxmodels | Date: Monday, 09.07.2012, 00:15 | Message # 18 |
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Observer
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| Hi again.. I wanted to add a discussion associated with this link to help with all of this. This link was referenced before but for convenience is below...
http://en.wikipedia.org/wiki/Betelgeuse#Circumstellar_dynamics
I have been through this wiki entry quite a few times in the past and have issues with some of the data as presented. That is not to say it is wrong, but perhaps, less well represented. The theoretical 'boiling convective cells' that might be imaged are actually highly likely expelled atmosphere forming the beginnings of a planetary slough-off surrounding the star. Other imaging at that link more clearly shows this 'extended' atmosphere. The star would be held at spherical shape but would be immersed in a nebulous shroud as the flares and atmospheric sloughing continues. This atmospheric shedding is also roughly spherical but with peaks and valleys in the outer extremities that roughly match the location of high stellar wind on the variably convective 'surface' of the star. Early imaging of Betelgeuse showed a lobe to one side that was interpreted as a rise off of the surface of a large convective cell. To be fair the data is not conclusive but at that link the other imagery shows a distended atmosphere consistent with early sloughing off of outer atmosphere and not massive mountains of convection on the stellar surface.
Sadly there is ONE illustration by the ESO on the link above that purports to show Betelgeuse with mountainous bubbles on it. While this diagram is correct for what it shows, it has been misinterpreted as meaning that these massive bubbles are always just sitting there. Every star can have flares and massive mass ejections. This is what was being represented on Betelgeuse, a massive mass loss event. The visible part of a star is called the Photosphere. If you look on that page you can see an image that shows the Photosphere and around it you see the distended envelope of atmosphere around the star. The Photosphere would be clearly visible as round and the nebulous detail would be thin, hot and transparent to the Photosphere.
I hope this is helpful.
M
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| Solaris | Date: Monday, 09.07.2012, 00:24 | Message # 19 |
 World Builder
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| Hi SovereignTripod,
Your answer is already here : http://en.spaceengine.org/forum/22-689-1#6060
Another similar thread : http://en.spaceengine.org/forum/11-737-1
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| Talyn | Date: Monday, 09.07.2012, 00:28 | Message # 20 |
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| Welcome to the forum SovereignTripod
Take some time to read the rules and enjoy the game 
At the risk of sounding like a broken record, this is a BIG forum so before asking a question, try to use the search function before posting questions that have multiple answers in multiple threads.
(Admins: May I suggest merging this thread with the other 2 mentioned by solaris?)
[Moderator notice] Done
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| SovereignTripod | Date: Monday, 09.07.2012, 01:25 | Message # 21 |
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Observer
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| I did try searching the forums before posting, I must have used bad keywords. Sorry about that, I'll do better next time. Thanks for the links Solaris, and thanks for the welcome Talyn.
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| HarbingerDawn | Date: Monday, 09.07.2012, 01:26 | Message # 22 |
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| Quote (fxmodels) The Photosphere would be clearly visible as round and the nebulous detail would be thin, hot and transparent to the Photosphere.
I hope this is helpful.
This is helpful, thank you. I understand what you're saying. At the present time, though, accurately modeling the appearance of that is not within SpaceEngine's capabilities, and if it's going to be wrong regardless then I think that SE prefers to err on the side of variety. When more advanced rendering techniques are implemented in the future, perhaps this more subtle effect could be implemented for giant stars.
Thank you for the input.
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| GoSpeed | Date: Saturday, 25.08.2012, 14:37 | Message # 23 |
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| One thing that I've had a question about was the depiction of red giants and carbon stars in SE. Somehow it didn't seem right. Then I saw this video and it made more sense. It is a graphic depiction of Betelgeuse, a star getting near to going supernova:
http://youtu.be/hJn-jmL_hyo
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| Voekoevaka | Date: Saturday, 25.08.2012, 14:50 | Message # 24 |
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| These "bubbles" on giant stars are caused by the convection movements of the gas layers. The lower layers recieve heat from the core, and so they become less dense. Then the Archimede force bring them to the upper layers.
Quote (GoSpeed) http://youtu.be/hJn-jmL_hyo
One more time it shows that the Space Engine stars could have a realistic shape.
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| HarbingerDawn | Date: Saturday, 25.08.2012, 17:54 | Message # 25 |
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| GoSpeed, this topic - and that animation - have already been discussed in other threads, all of which have now been merged here. Before posting any new threads, try running a search to see if any other related threads already exist; this is to reduce forum clutter and maintain ease of navigation. A search for "red giant" would have immediately revealed this thread.
You should also take a moment and read the forum rules, if you haven't already.
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| GoSpeed | Date: Thursday, 30.08.2012, 03:35 | Message # 26 |
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| Well what what better way to be fully welcomed to a forum then to be chastised by the esteemed Moderator! Message received  . I'll do better next time.
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| HarbingerDawn | Date: Thursday, 30.08.2012, 05:24 | Message # 27 |
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| Quote (GoSpeed) Well what what better way to be fully welcomed to a forum then to be chastised by the esteemed Moderator!
Sorry I didn't mean to sound snappy. I just have to say that sort of thing so often that I can be pretty terse when I'm during a busy period on the forum. There's been a rapid influx of new members in the past few days and I'm the only mod around to welcome people, so sometimes someone doesn't get the most polite welcome. Sorry 
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| Kimb | Date: Wednesday, 16.01.2013, 04:53 | Message # 28 |
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| Maybe there should be an option in future verzions of SE between depicting giant stars as 'bubbly' and depicting them as round; that way users on both sides of the debate can be happy......:)
Edited by Kimb - Wednesday, 16.01.2013, 04:54 |
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| HarbingerDawn | Date: Wednesday, 16.01.2013, 10:13 | Message # 29 |
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| Quote (Kimb) Maybe there should be an option in future verzions of SE between depicting giant stars as 'bubbly' and depicting them as round; that way users on both sides of the debate can be happy......:)
This would be a terrible idea to implement. It would give an entirely inconsistent experience for SE. Also, there is no "two sides" thing at work here, there is only truth; stars are as they are. The best that we can do is to go with whatever the best data that we have is, and where the data equally supports two different ideas then we should err on the side of variety. At most, they should be rendered differently based on their bulk properties. I agree that stars could use some work and that the red giants as currently depicted are rather cartoonish and comical, but it is still better to represent them as such than as smooth spheres.
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| apenpaap | Date: Wednesday, 16.01.2013, 10:57 | Message # 30 |
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| Yeah, while the current red giants could use some work, I certainly like their oddness over having giants look like normal stars.
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