Celestia Forums

Hello,

Please, see this image : http://en.wikipedia.org/wiki/File:Taran ... detail.jpg

Why Celestia can't show stars like these bright ones(those which seem to appear in the center of a cross)?
Very exciting and stars feel very hot and bright, don't they?

Because this effect is due to the camera and is not visible in reality.

What do you mean by this is not reality? I want to say that we see universe according the means we use, don't we? We use Eyes, Camera...
How does Celestia allow us to view universe? Through human eyes in space? I think this is not clear in my mind, i found anywhere where this is well explained...

However, these light effects (common now in video games) wouldn't be interesting to see universe in Celestia thought a camera view then ? According the choice of the user?
Most of people who discovers universe is throught these Hubble images. Don't you think they want to find these kind of image in first uses of Celestia? How do they feel disapointed to only see "reality" as Celestia actually shows? What may they think about the program then?

Imy wrote:What do you mean by this is not reality? I want to say that we see universe according the means we use, don't we? We use Eyes, Camera...
How does Celestia allow us to view universe? Through human eyes in space? I think this is not clear in my mind, i found anywhere where this is well explained...

However, these light effects (common now in video games) wouldn't be interesting to see universe in Celestia thought a camera view then ? According the choice of the user?
Most of people who discovers universe is throught these Hubble images. Don't you think they want to find these kind of image in first uses of Celestia? How do they feel disapointed to only see "reality" as Celestia actually shows? What may they think about the program then?

Yes, Celestia philosophy is to depict what you would see if you were there in person. And you rise a crucial problem; people are too used to see false color marvelous nebulas and Galaxies, star fields when you wouldn't see anything etc... so the question is : must we follow the tendency and show something wrong just because it's beautiful or could it better to tell people that reality are not these beautiful images? Perso I agree with the way Celestia is taking; later if wavelength filtering is implemented, you will theoretically see in Celestia the hubble shots, but then people will be conscious that they have turned on filtering and that what they are seeing is beyond their physical/physiological capacities.

Edit: AND you are right, that is VERY important and should be notify in the read me... Chris?

Just 2-cents worth from the Brain-Dead here...

I absolutely love the way in which Celestia depicts objects as they actually ARE.
Please don't change this philosophy. This is what makes Celestia the spectacular
application that it is today.

Again, just 2-cents worth from the Brain-Dead.

I'm with you Bob! Celestia's just fine the way it is thank you.

It's not in my mind to change current stars in Celestia, I only suggest to enlarge and accurate the way they're shown.

A large part of images from space comes from cameras, that's to say camera images are as important as eye view of space.

ElChristou, you've said that Celestia, today, shows space throught human eyes, but Celestia can (without warning basic user) go further than classic human eyes capabilities, what about magnitude range in Celestia for instance?

Like Celestia uses double way for showing texture on planets (chose by users : a computer one and a limit acknowledge one)would not be interesting to have a camera view and an eye view? Wouldn't be the best way to show the difference between them, and also show how reality of space depends from the tool your are using?

Diffraction is reality. This is an exemple of an rectangular diffraction pattern (like camera pixels) :
http://www.univ-lemans.fr/enseignements ... prect.html

Imy wrote:It's not in my mind to change current stars in Celestia, I only suggest to enlarge and accurate the way they're shown.

That is precisely what Celestia want to do! The idea is to depict the body as it is and not has it appears through a hardware...

Imy wrote:A large part of images from space comes from cameras, that's to say camera images are as important as eye view of space.

What makes you say that?

Imy wrote:ElChristou, you've said that Celestia, today, shows space throught human eyes, but Celestia can (without warning basic user) go further than classic human eyes capabilities, what about magnitude range in Celestia for instance?

Of course, but I guess there is quite a difference between a feature build for a practical purpose and a feature that is just eye candy...

Imy wrote:Like Celestia uses double way for showing texture on planets (chose by users : a computer one and a limit acknowledge one)would not be interesting to have a camera view and an eye view? Wouldn't be the best way to show the difference between them, and also show how reality of space depends from the tool your are using?

Sure, but again a feature that help you understanding the nature of things do have an interest while trivial features like lens flare or diffraction effects are (in the frame of Celestia) nothing less than eye candy. The next step for Celestia would be to render the scene through wavelength filtering. That would be another feature that is not (of course) linked to human vision but which is important for the understanding of astrophysics. Remember Celestia is not a game but more an app dedicated to collect data...

Imy wrote:Diffraction is reality. This is an exemple of an rectangular diffraction pattern (like camera pixels) :
http://www.univ-lemans.fr/enseignements ... prect.html

Of course diffraction is real; now I guess that if Celestia was a camera simulation, then yes this kind of artifact would have it's place in the soft...

Now, if you want to continue arguing on this topic, I'll let someone else explain you better because I can only explain you want I understood of Celestia philosophy from a end user point of view...

If you want stars to look bright and pretty like in the photographs, set the star style to scaled discs and up the magnitude.
Celestia is so customizable you can pretty much set it to look anyway you want it to.

I also agree that Celestia should render stars as they are. I just tend to have different opinions as to how stars look, based on what I've seen of our own sun with my own eyes, and how it appears in Celestia.

e.g. With the exception of the obvious lens flares, here's about how my eyes perceive the sun (yes, this is an image of the sun taken from a distance of ~ 1 AU):


Here is how the sun appears from Earth in Celestia, (again, at a distance of ~1 AU).


The trained eye might notice some differences.

Sure, one might argue that a computer monitor cannot represent the sun 100% accurately because it's not designed to get that bright--and this is true. The first image is, however, a pretty convincing representation of the sun. Whereas the second image ... isn't...

I don't buy the "your eyes adapt to the lighting level" argument. Staring at the sun for a few seconds, I find the pain in my eyes much more overwhelming than their adjusting. If I were wearing a welding helmet, then sure, I could see how the sun would be rendered as I see it in Celestia.

Anyway, that's just my opinion. I might be super-photosensitive and simply be completely mistaken about how the sun looks.

EDIT
Decided to do some research, and it seems that there is a lot of evidence on the internet to suggest the sun is a fairly bright body.
http://farm1.static.flickr.com/89/28284 ... ae8982.jpg
http://scratchbrain.com/images/snap/2/B ... -sajpy.jpg
http://www.maison-de-stuff.net/john/pic ... MG0417.JPG



Guys, some of you know I've been complaining about the stars in Celestia for quite some time. It's something that I feel needs desperate improvement and has been ignored for a very long time. It is claimed that Celestia is geared toward representing objects as they are. I cannot take this seriously when I think about how I see the sun, and other stars, in Celestia.

Would it be hard to have a "Realistic Stars" or "bright stars" option in the settings? If users want to have science-fiction-style stars, then there's no need to deprive them of that. Having a choice between bright stars, and the current setting, would definitely be a step forward to presenting the stars in Celestia a bit more realistically, and could satisfy both groups (the ones who prefer the current settings, and those who prefer bright stars).

Reiko wrote:Celestia is so customizable you can pretty much set it to look anyway you want it to.

The next step for Celestia would be to render the scene through wavelength filtering. That would be another feature that is not (of course) linked to human vision but which is important for the understanding of astrophysics. Remember Celestia is not a game but more an app dedicated to collect data...

I agree with you that spectral range for viewer in Celestia would be useful, and it is a great expected step! I agree with you that Celestia learns us about astronomy, astrophysic and how universe is. The program has to follow a continously more realistic development. But I misagree when you tell that Celestia is only a collecting data program : in this case why a graphical interface is continously improved in a way of photorealism ? This is how this computer program appears to me. Indeed, Celestia seems to have a double aim, a beautiful computer program and a realistic one and this idea appears in this double function for texturing planet, a graphical one and an other more realistic. If Celestia was a realistic program, only black and white limit of acknowledge texture would exist... I wonder if Celestia was started as a very realistic program if today we would have only eight planets at all. I want to say that you have to accept that Celestia is filling the lack of information by some things from imagination, otherwise, so no exoplanets, no stars except sun... only catalogs numbers for advanced users! Celestia is made use some stuffs used to build game.

My bright stars appears as a backwards development, and then it seems wrong for you but it isn't. Well, it's even an additional feature to improve Celestia in a way of graphical aim and a realistic purpose. This feature would specify more clearly how you see universe in Celestia. It makes everyone to accept view hardware edges. This is candy, well, but it's a learnful stuff too!

I accept idea that you prefer dealing with physical concept as magnitude, spectral range instead of more obvious general and technical concepts as eye view or camera view which are composites. But in this case Celestia lacks diffraction so.

The idea is to depict the body as it is and not has it appears through a hardware...

You're wrong here : your are using eye hardware anyway, aren't you?

If you want stars to look bright and pretty like in the photographs, set the star style to scaled discs and up the magnitude.

Well, I always wonder if this feature is real or not... I've told me that is the result of a photograph plate overexposed, is right or not?

If you want the flare effect in images taken from Celestia you can add it afterwards using the 'sparkle' effect in Gimp. (a free program).

I am annoyed to see so few opinions to enlarge and precise how celestia shows you universe. I have to use then outside programs for end graphical effects on image then, thanks. My idea have been summed up only to these graphical purposes whereas probably, it was larger aim and reveals to the user how reality depends of the tool you used (eyes is one of them). Now i'm expecting than someday celestia will have spectral viewing capabilities !

The crosses seen on star images are caused by the supports for the secondary mirror in a reflecting telescope diffracting the light. The most common mounting for secondary mirrors use four rods, hence it create four spikes.

The eye is not without its own imaging artifacts. A bright light source diffracts from the layers of the lens. This causes the appearance of rays shooting out from a bright light source. If the eye was without imaging artifacts we would probably see stars as bright points without any rays.

four rods, hence it create four spikes

That means that spikes numbers are linked to hardware rod number..

The eye is not without its own imaging artifacts. A bright light source diffracts from the layers of the lens. This causes the appearance of rays shooting out from a bright light source. If the eye was without imaging artifacts we would probably see stars as bright points without any rays.

Ah! Eye is not perfect ; so celestia doesn't simulate universe throught human's eyes finally, but rather as a perfect idea that we make of it (which is interesting too)

Imy wrote:...so celestia doesn't simulate universe throught human's eyes finally, but rather as a perfect idea that we make of it (which is interesting too)

Yep, it's a better way to depict Celestia's rendering...

ElChristou wrote:

Imy wrote:...so celestia doesn't simulate universe throught human's eyes finally, but rather as a perfect idea that we make of it (which is interesting too)

Yep, it's a better way to depict Celestia's rendering...

Yes, it is. This sentence should be shown (and understood) as a warning for all users then !

Imy wrote:

ElChristou wrote:

Imy wrote:...so celestia doesn't simulate universe throught human's eyes finally, but rather as a perfect idea that we make of it (which is interesting too)

Yep, it's a better way to depict Celestia's rendering...

Yes, it is. This sentence should be shown (and understood) as a warning for all users then !

You're right!

Imy wrote:

four rods, hence it create four spikes

That means that spikes numbers are linked to hardware rod number..

The eye is not without its own imaging artifacts. A bright light source diffracts from the layers of the lens. This causes the appearance of rays shooting out from a bright light source. If the eye was without imaging artifacts we would probably see stars as bright points without any rays.

Ah! Eye is not perfect ; so celestia doesn't simulate universe throught human's eyes finally, but rather as a perfect idea that we make of it (which is interesting too)

Nothing like jumping in at the tail-end of a discussion.

When dealing with a telescope's image as bdm points out, yes. Otherwise, such as Hungry4info's picture, the effect is usually a result of the camera optics, the lens material itself not having uniform optical characteristics. This can cause light to be scattered internally in the lens, which then can cause reflections.

Lord Ferret wrote:the effect is usually a result of the camera optics, the lens material itself not having uniform optical characteristics. This can cause light to be scattered internally in the lens, which then can cause reflections.

I see these in my own eyes, too.