Yeah, in the next version you will be able to customize star sprite appearance more.  It is possible to get closer to either a photo-realistic "astrophotography" look like in those images, or something more like what the eye sees:

Idk, something about it makes the star sprites look really fake. Especially the brightest ones.
Also hopefully this can be achieved. Though I'm not sure if Smoke_ring_for_a_halo.jpg is realistic since it was taken by a telescope.

Star spikes in photographs are caused by diffraction around the support rods of the secondary mirrors of reflection telescope (usually four spikes) or diffraction due to a non-circular aperture (one spike for every iris blade).  Your eye's iris is pretty round, but you can see similar spikes from your eyelid, eyebrow, whatever obstructs the light passage somewhat (try to look at bright light sources with the eyes partly shut). When I do night time photography, I generally prefer a wide open aperture to avoid diffraction spikes, which is personal preference.  Also, I want to collect as much light as possible, so a wide open aperture is good (but perfect focus is harder then).

Star spikes in photographs are caused by diffraction around the support rods of the secondary mirrors of reflection telescope (usually four spikes) or diffraction due to a non-circular aperture (one spike for every iris blade).  Your eye's iris is pretty round, but you can see similar spikes from your eyelid, eyebrow, whatever obstructs the light passage somewhat (try to look at bright light sources with the eyes partly shut). When I do night time photography, I generally prefer a wide open aperture to avoid diffraction spikes, which is personal preference.  Also, I want to collect as much light as possible, so a wide open aperture is good (but perfect focus is harder then).

Oh I know about diffraction spikes around stars. I was talking more about the Corona like structure around the star, along with the general lighting of the Sprite.

Well again you can tweak these options to probably get something more like the effect you're going for.  Your mileage may vary because it's really hard to understand exactly what you're going for with words or with different styles of astrophotographs.

Like, in some astrophotographs the center of the stars are white.  Sometimes they're colored.  Sometimes the overall coloration of all the stars is very strong, sometimes it's desaturated.  The relative sizes of the stars in the image may vary with brightness differently.  It all depends on how the images were taken and even more importantly how they were processed on the computer.  Artistic choice and aesthetic are a huge factor in astrophotography, usually more so than "realism".

Well again you can tweak these options to probably get something more like the effect you're going for.  Your mileage may vary because it's really hard to understand exactly what you're going for with words or with different styles of astrophotographs.

Like, in some astrophotographs the center of the stars are white.  Sometimes they're colored.  Sometimes the overall coloration of all the stars is very strong, sometimes it's desaturated.  The relative sizes of the stars in the image may vary with brightness differently.  It all depends on how the images were taken and even more importantly how they were processed on the computer.  Artistic choice and aesthetic are a huge factor in astrophotography, usually more so than "realism".

I think my images are a bit desaturated so that's why the corona structure is visible. Got any real images of stars that seem the most realistic (apparent to the human eye).

Can I have some clarification on stars? How can this Red Dwarf be so small and massive enough to maintain nuclear fusion but these Gas Giants are several times larger but less massive. 

Can I have some clarification on stars? How can this Red Dwarf be so small and massive enough to maintain nuclear fusion but these Gas Giants are several times larger but less massive. 

I think it's because inside a certain range that starts beyond double the Jupiter mass, gravity is strong enough to crush the object inside a smaller size than ones with less two 2 JMs

Got any real images of stars that seem the most realistic (apparent to the human eye).

Go outside and look at the stars.  It will be more realistic than any image.

I'm not intending to sound sassy -- it's true!  Cameras just don't see the same way we do when it comes to the night sky.  The human eye has a much wider dynamic range than a camera sensor. The human eye also loses sensitivity to color in dim light, whereas a camera does not.

Same for astrohoptography vs. how things look through a telescope.  For example, this is the closest approximation I've ever found for how the Orion nebula appears through a scope:

Notice it is a sketch. It more accurately represents how the eye sees it than any astrophoto.  You barely see any color, and it is mostly a subdued green.  The eye is more sensitive to green light than to red or violet light.  Astrophotos will bring out all the colors, and more of the details that are too faint for us to see.

Got any real images of stars that seem the most realistic (apparent to the human eye).

Go outside and look at the stars.  It will be more realistic than any image.

I'm not intending to sound sassy -- it's true!  Cameras just don't see the same way we do when it comes to the night sky.  The human eye has a much wider dynamic range than a camera sensor. The human eye also loses sensitivity to color in dim light, whereas a camera does not.

Same for astrohoptography vs. how things look through a telescope.  For example, this is the closest approximation I've ever found for how the Orion nebula appears through a scope:

Notice it is a sketch. It more accurately represents how the eye sees it than any astrophoto.  You barely see any color, and it is mostly a subdued green.  The eye is more sensitive to green light than to red or violet light.  Astrophotos will bring out all the colors, and more of the details that are too faint for us to see.

Yeah, and the stars look very realistic too. They sorta ''pop'' out and it gives me a feeling of dynamic lighting, instead of static and single-colored. I could also see some corona like structure around the brightest stars. SE has pretty much all of this nailed down, but for some reason it just doesn't look right, you know? I don't know why I feel this way. :L

But anyways, thanks for the image! One final question, how does the surface of massive stars look compare to less massive stars (i.e, the photosphere or whatever is visible to the naked eye if you discount the intense light.) Some stars have different convection and radiative zones, which I guess would affect the appearance of the surface. Not only that, they have fast stellar winds as well. Would it be like a fast moving plasma moving away from the star?

Can I have some clarification on stars? How can this Red Dwarf be so small and massive enough to maintain nuclear fusion but these Gas Giants are several times larger but less massive. 

Puffy Planets

The red dwarf is normal and achieves fusion without a problem.  The gas giants achieve larger size because they are lower density -- they have less mass and their atmospheres are puffed up by the heating.  Such planets are observed in nature!  For example Wasp-17b is only about half the mass of Jupiter, but twice its size.  There are known red dwarfs that are smaller than this!

These puffed up giants cannot undergo fusion because the core temperature and density are not high enough.  They have too little mass to reach those conditions.

how does the surface of massive stars look compare to less massive stars

Although high mass stars are considered to be radiative-dominated in the outer envelopes, there is still a thin upper convective layer, driven by the cooling from the surface radiating to space.  Across the main sequence, hotter stars have smaller, more intense granules (the upward flow, which appears as the bright centers), and cooler stars have larger granules with more concentrated downward flow (the darker regions between the granules).

In evolved stars (giants) the surface gravity is much less which allows the "granules" to become enormous -- more like a few giant blobs that visibly distort the shape of the star.  This is a famous source of confusion to people coming across it in Space Engine.

As for the solar winds, you wouldn't see them unless blocking the star as with a solar eclipse.  The speed of the solar wind for high mass stars is typically about 3 times the escape speed from the photosphere.  

 and cooler stars have larger granules with more concentrated downward flow (the darker regions between the granules).

Any examples of this (simulation or artistic depiction)? Wondering how that would look like.
But the granules themselves wouldn't have different morphology due to the heat/convection differences? They'll be like the sun's?
What about solar prominences? 

Puffy planet

Speaking of small red dwarf stars, past M8.0 V, they get a lot smaller than Saturn, at M9.3 V, smaller than Uranus.
I found one twice the size of Earth. Why does SE make them this small? Is it realistic? If so, what can compress a main sequence star so much? Look at the density, just a bit behind a white dwarf.

The smallest possible star size, or brown dwarf limit, is about 8.7% of the Sun, or 60,000km in radius.  That's a bit smaller than Jupiter, or about 10 times the size of Earth.  So Space Engine's algorithm does need some adjustment.

Any examples of this (simulation or artistic depiction)? Wondering how that would look like.

Most of this comes from modeling in a more symbolic sense with purposes for comparison to observations of spectral lines, but there are some hydrodynamical simulations that produce more intuitive images.






[youtube]hJn-jmL_hyo[/youtube]

The smallest possible star size, or brown dwarf limit, is about 8.7% of the Sun, or 60,000km in radius.  That's a bit smaller than Jupiter, or about 10 times the size of Earth.  So Space Engine's algorithm does need some adjustment.

Any examples of this (simulation or artistic depiction)? Wondering how that would look like.

Most of this comes from modeling in a more symbolic sense with purposes for comparison to observations of spectral lines, but there are some hydrodynamical simulations that produce more intuitive images.






[youtube]hJn-jmL_hyo[/youtube]

Thank you! Are the bottom left images in the bottom image that of massive stars?

No, the mass decreases from left to right and down, like reading text.  The main sequence goes OBAFGKM, from most to least massive.  O's and B's aren't shown here and are generally thought to lack these surface features.  We do know that A's show granulation and fit the pattern.