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Fiery Phoenix
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Possible bug: Incorrect calculation of radii/luminosities of procedural B-type stars

27 Feb 2020 08:11

I've noticed that the calculated luminosities and radii of many procedurally generated B-type stars simply don't make sense. Using the well-known Stefan-Boltzmann equation, I always seem to end up with radically different values from what SE displays. For instance, a B0 V star with a radius of 6.36 solar radii and temperature of 29220 K will have a luminosity of about ~26900 Sols, yet SE calculates its luminosity to be a measly 539 sols, which is a huge deviation from the value suggested by the equation. Lots of other examples in-game, but the same core problem persists. 

As far as I can tell, this issue is mainly with B-type main sequence stars. Their luminosities often don't align with their temperatures and radii and are considerably lower than they should be, which leads me to think the procedural generation algorithm is not applying the Stefan-Boltzmann law correctly.  
 
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longname
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Possible bug: Incorrect calculation of radii/luminosities of procedural B-type stars

01 Mar 2020 05:23

Fiery Phoenix wrote:
Source of the post For instance, a B0 V star with a radius of 6.36 solar radii and temperature of 29220 K will have a luminosity of about ~26900 Sols, yet SE calculates its luminosity to be a measly 539 sols

Which one is correct, then?
[dah<500,26>dah<180,14>dah<180,21>dah<500,19>dah<180,26>dah<500,21>]
 
Fiery Phoenix
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Possible bug: Incorrect calculation of radii/luminosities of procedural B-type stars

01 Mar 2020 08:02

longname wrote:
Fiery Phoenix wrote:
Source of the post For instance, a B0 V star with a radius of 6.36 solar radii and temperature of 29220 K will have a luminosity of about ~26900 Sols, yet SE calculates its luminosity to be a measly 539 sols

Which one is correct, then?

Though it was obvious; the former is the correct calculation. There's no way a star with that radius and temperature would only be ~500 times as luminous as the Sun. 

Use this calculator to see what I mean.

I'm hoping this is addressed in a future update. It was probably an oversight. 
 
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longname
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Possible bug: Incorrect calculation of radii/luminosities of procedural B-type stars

03 Mar 2020 14:51

Fiery Phoenix wrote:
longname wrote:
Fiery Phoenix wrote:
Source of the post For instance, a B0 V star with a radius of 6.36 solar radii and temperature of 29220 K will have a luminosity of about ~26900 Sols, yet SE calculates its luminosity to be a measly 539 sols

Which one is correct, then?

Though it was obvious; the former is the correct calculation. There's no way a star with that radius and temperature would only be ~500 times as luminous as the Sun. 

Use this calculator to see what I mean.

I'm hoping this is addressed in a future update. It was probably an oversight. 

And what data supports which calculation?
[dah<500,26>dah<180,14>dah<180,21>dah<500,19>dah<180,26>dah<500,21>]
 
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evildrganymede
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Possible bug: Incorrect calculation of radii/luminosities of procedural B-type stars

04 Mar 2020 20:58

longname wrote:
And what data supports which calculation?

Actual science and reality?
e.g. B0 V star - https://en.wikipedia.org/wiki/Tau_Scorpii
either way, their Luminosity should be in the tens of thousands of sols, not hundreds.
 
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Possible bug: Incorrect calculation of radii/luminosities of procedural B-type stars

05 Mar 2020 15:08

evildrganymede wrote:
longname wrote:
And what data supports which calculation?

Actual science and reality?
e.g. B0 V star - https://en.wikipedia.org/wiki/Tau_Scorpii
either way, their Luminosity should be in the tens of thousands of sols, not hundreds.

Thanks for actually proving your calculation was correct, didn't take long did it?
[dah<500,26>dah<180,14>dah<180,21>dah<500,19>dah<180,26>dah<500,21>]
 
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evildrganymede
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Possible bug: Incorrect calculation of radii/luminosities of procedural B-type stars

06 Mar 2020 07:32

If you knew anything about astronomy (obviously the larger luminosity value was the more correct one, plus the Mass-Luminosity relationship used in the calculation is even actually explained right there on the website and is quite well established) and could have been bothered to do a simple search yourself, it wouldn't have been necessary. Make a bit of effort yourself instead of demanding it from others.
 
A-L-E-X
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Possible bug: Incorrect calculation of radii/luminosities of procedural B-type stars

06 Mar 2020 14:31

Hopefully this gets fixed.  I saw this mass-luminosity relationship in Starry Night's H-R diagram, and since Vlad had said that he might add this feature to Space Engine, maybe we will see a fix for this relationship soon.
 
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Possible bug: Incorrect calculation of radii/luminosities of procedural B-type stars

07 Mar 2020 08:52

A-L-E-X wrote:
Hopefully this gets fixed.  I saw this mass-luminosity relationship in Starry Night's H-R diagram, and since Vlad had said that he might add this feature to Space Engine, maybe we will see a fix for this relationship soon.

Hoping for the same. It's quite a serious miscalculation, and it doesn't seem to only affect B-type stars. I've seen procedural red giants with the same issue, with luminosities far lower than the Stefan-Boltzmann law suggests. 
 
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evildrganymede
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Possible bug: Incorrect calculation of radii/luminosities of procedural B-type stars

07 Mar 2020 09:19

Not sure if Red Giants follow that the Mass-Luminosity relationship, I think it only applies to Main Sequence stars? 
 
Fiery Phoenix
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Possible bug: Incorrect calculation of radii/luminosities of procedural B-type stars

07 Mar 2020 10:10

evildrganymede wrote:
Not sure if Red Giants follow that the Mass-Luminosity relationship, I think it only applies to Main Sequence stars? 

That's true. In the case of red giants, you can estimate the luminosity based on their radii and surface temperatures using this equation
 
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Watsisname
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Possible bug: Incorrect calculation of radii/luminosities of procedural B-type stars

09 Mar 2020 00:12

Yes, the Stefan-Boltzmann law is the more fundamental one (it applies to all objects that behave as blackbodies, which is good approximation for all stars), and it is so important in astronomy and physics that it really shouldn't have needed to be justified. Your observation of the error was correct.

We can also make the calculation a little more simple when we know the star's temperature and its radius in solar units. Then the luminosity in solar units is

Image


Consider a star 6 times the radius of the Sun, with a temperature of 29,000K (about 5 times the Sun's temperature of 5800K). Square the 6 (that's 36) and raise the 5 to the 4th power (that's 625). Multiply 36 and 625 together, and that's 22,500 times the luminosity of the Sun. (The star you posted in the OP is a little bigger and a little hotter so it is even more luminous than this.)


I'm not sure of the cause for this error. I looked in earlier versions and could not find it in any O or B stars -- their luminosities appeared to be perfectly consistent with the Stefan-Boltzmann Law. I'll make sure that this is brought to SpaceEngineer's attention. Thanks for reporting it!
 
Fiery Phoenix
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Possible bug: Incorrect calculation of radii/luminosities of procedural B-type stars

10 Mar 2020 01:32

Watsisname wrote:
(…)

I'm not sure of the cause for this error. I looked in earlier versions and could not find it in any O or B stars -- their luminosities appeared to be perfectly consistent with the Stefan-Boltzmann Law. I'll make sure that this is brought to SpaceEngineer's attention. Thanks for reporting it!

Glad to hear it. If you need specific examples from in-game (ver 0.990), I would be happy to provide you with a few. 
Thanks for stopping by! 

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