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Mouthwash
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How galaxies/nebulae actually look.

09 Nov 2017 19:38

I'm a bit concerned over Space Engine's representation of them... while making them look exactly how they would to the naked eye isn't feasible (or fun), I don't like the idea of seeing totally false colors or shapes. How realistic are the depictions?

1. It seems like nebulae are going to be totally false color in the next version, which is disappointing. Correct me if I'm wrong, but those pictures don't give me an impression of realism.

2. How much of the visible light of galaxies is generated by stars? Seems like the star density in SE above the Milky Way's core is just as thick as in the arms, but that isn't shown in the galaxy model. If this is realistic, then maybe the arms are more visible due to having lots of gas/dust.
 
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Watsisname
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How galaxies/nebulae actually look.

09 Nov 2017 23:32

Mouthwash wrote:
Source of the post 1. It seems like nebulae are going to be totally false color in the next version, which is disappointing. Correct me if I'm wrong, but those pictures don't give me an impression of realism.

False color images of nebulae are pervasive, but false color does not necessarily mean wrong color.  Sometimes astrophotos are taken through specific wavelength filters and then those images are mapped to totally different colors, or they may map non-visible wavelengths to visible colors, which of course will look very unlike how the real thing looks to the eye or even a long exposure with a typical color camera.  But other times the images may be mapped to the same color that the filter transmits, in which case the result is pretty close to true color.

To get an idea of the true colors of a nebulae, a helpful tool is to spread its image out into a spectrum, as in a "slitless spectrograph".  Here's an example for the Cat's Eye Nebula (top) and Ring Nebula (bottom).

Image

The primary colors are red and a greenish turquoise.  Red is from the hydrogen-alpha line, while the turquoise comes from Hydrogen-beta and Oxygen-III.  Which matches up pretty well with the following astrophotographs:

► Show Spoiler


So the true color of nebulae actually is pretty close to what the SE snapshots show.

2)  The majority of a galaxy's luminosity in visible wavelengths is from stars.  Dust dims and reddens the visible light that passes through it and re-emits in infrared.  Clouds of neutral gas are non-luminous (they glow in radio instead).  So the only real visibly luminous feature of galaxies besides stars is ionized gas, which glows with the characteristic redish-pink of hydrogen, and is the main feature of star formation regions.
 
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problemecium
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How galaxies/nebulae actually look.

11 Nov 2017 16:34

Also you can roughly approximate naked-eye appearance for galaxies and nebulae by cranking down the "models lighting" or "GlowMagnLimit" (depending on your version) variable in your config file to 0 or 1. I currently have mine at 2 so I have a balance of realism and visibility.

P.S.: Neat post, Watsisname!
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Formerly known as "parameciumkid." Still playing on Intel HD Graphics 4000 ^^
 
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Mouthwash
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How galaxies/nebulae actually look.

13 Nov 2017 02:15

Watsisname wrote:
Mouthwash wrote:
Source of the post 1. It seems like nebulae are going to be totally false color in the next version, which is disappointing. Correct me if I'm wrong, but those pictures don't give me an impression of realism.

False color images of nebulae are pervasive, but false color does not necessarily mean wrong color.  Sometimes astrophotos are taken through specific wavelength filters and then those images are mapped to totally different colors, or they may map non-visible wavelengths to visible colors, which of course will look very unlike how the real thing looks to the eye or even a long exposure with a typical color camera.  But other times the images may be mapped to the same color that the filter transmits, in which case the result is pretty close to true color.

To get an idea of the true colors of a nebulae, a helpful tool is to spread its image out into a spectrum, as in a "slitless spectrograph".  Here's an example for the Cat's Eye Nebula (top) and Ring Nebula (bottom).

Image

The primary colors are red and a greenish turquoise.  Red is from the hydrogen-alpha line, while the turquoise comes from Hydrogen-beta and Oxygen-III.  Which matches up pretty well with the following astrophotographs:

► Show Spoiler


So the true color of nebulae actually is pretty close to what the SE snapshots show.

So the whole new nebula system is based on this?

Mouthwash wrote:
2)  The majority of a galaxy's luminosity in visible wavelengths is from stars.  Dust dims and reddens the visible light that passes through it and re-emits in infrared.  Clouds of neutral gas are non-luminous (they glow in radio instead).  So the only real visibly luminous feature of galaxies besides stars is ionized gas, which glows with the characteristic redish-pink of hydrogen, and is the main feature of star formation regions.

Then why is there a thick glob of stars extending above and below the galactic core? Is something smothering their light, or is this an inaccuracy in SE?
 
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Watsisname
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How galaxies/nebulae actually look.

13 Nov 2017 08:45

I couldn't say if that's specifically what it is based on. Only that the colors and shapes in the previews look pretty faithful to real nebulae.

As for the light extending above and below the core, perhaps you're seeing the galactic bulge.
 
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Mouthwash
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How galaxies/nebulae actually look.

15 Nov 2017 20:55

Watsisname wrote:
As for the light extending above and below the core, perhaps you're seeing the galactic bulge.

I'm *not* seeing light. I'm seeing lots of stars, but no indication from a distance that anything is there.
 
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Watsisname
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How galaxies/nebulae actually look.

16 Nov 2017 01:35

Sorry I misunderstood.  But I think that this makes sense:

Reality:

Image

Space Engine:

Image

The stars of the galactic bulge are visible from a distance in a manner quite consistent with reality.  Yes, from up close you can see stars and globular clusters at a greater distance from the core, but think about their density compared to closer to the center.  From a distance, that outer bulge and galactic halo is less visible compared to the more star-rich inner regions and the disk.  Nothing is blocking the light, there just isn't as much of it.
 
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XBrain130
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How galaxies/nebulae actually look.

16 Nov 2017 06:06

I think they're talking about this:

scr00052.png


This is actually somewhat wrong: the spherical blob around the core bulge should envelop the entire galaxy instead :P
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Mouthwash
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How galaxies/nebulae actually look.

20 Nov 2017 23:32

Huh, looks like I was wrong. After looking in the search browser, it appears that the stars above and below the bulge are actually an order of magnitude sparser than the stars in the disk. They looked almost identical when I was flying around them. :?

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