User-added stars appear huge from a distance

[aurora]

I've encountered this bug when I started to add fictional stars. Close up they look all right, but from a distance of about 1 to 10 LY they appear as freakishly huge bright discs the size of pennies when viewed in any mode but point. Real (existing) HIP stars do not exhibit this behaviour. Is there a workaround?

OS: Windows XP
Graphic card: ATI Radeon Mobile 9700
Celestia: 1.6.0

[selden]

Please provide an example of an STC file which produces these results.

(My suspicion is that you've exchanged AbsMag and AppMag values.)

[selden]

I managed to generate something similar to what you might be seeing.

While viewing a star and using the mousewheel to change the viewpoint's distance from it, at one particular distance, the star seemed to have a sudden increase in brightness. However, it wasn't the distant star that was being drawn bright, it was our own Sun getting in between the Star and the viewpoint. I had started looking at the star from a position near the Earth, with the Sun behind the viewpoint. I then moved closer to the star using only the mousewheel. The star got brighter. I then moved away from the star using only the mousewheel. It got dimmer as expected, and then suddenly seemed to flare up. But I wasn't seeing the original star any more. It was our Sun. The mousewheel had moved the viewpoint to its other side. Note that the alignment doesn't have to be perfect. The brightness of the Sun will interpose itself for quite large offsets.

Below is a picture showing this situation. Viewpoint #1 is looking at the star from near the Earth, so the star is dim; viewpoint #2 is looking at from nearby, so it's bright; and viewpoint #3 is looking toward the star from a greater distance where it should be very dim, but the Sun is in the way and very bright.

Might this be what you're seeing?

[aurora]

Here is my STC.

Barycenter "TridentSystemHub:Greater Trident"
{
RA 219.899437 #
Dec -60.835401 #
Distance 300.0
}
Barycenter "TridentSystemMainSal:Trident and Salamander"
{
OrbitBarycenter "TridentSystemHub"

EllipticalOrbit {
Period 3455.2506
SemiMajorAxis 146.00 # mass ratio 2:1.4
Eccentricity 0.02
Inclination 96.2
AscendingNode 73.5
ArgOfPericenter 76.4
MeanAnomaly 241.7
}
}
Barycenter "TridentSystemMainSimp:Trident and Simplicissimus"
{
OrbitBarycenter "TridentSystemMainSal"

EllipticalOrbit {
Period 760.85
SemiMajorAxis 35.00 # mass ratio 1.3:0.7
Eccentricity 0.19
Inclination 82.22
AscendingNode 67.30
ArgOfPericenter 4.02
MeanAnomaly 200.13
}
}
999999 "Trident" # TridentMain
{
OrbitBarycenter "TridentSystemMainSal"
SpectralType "F6V"
AppMag 8.244

EllipticalOrbit {
Period 760.85
SemiMajorAxis 35.00 # mass ratio 1.3:0.7
Eccentricity 0.19
Inclination 82.22
AscendingNode 67.30
ArgOfPericenter 4.02
MeanAnomaly 200.13
}
}
999998 "Salamandra" # Salamander
{
OrbitBarycenter "TridentSystemMainSal"
SpectralType "K4V"
AppMag 11.395

EllipticalOrbit {
Period 760.85
SemiMajorAxis 75.00 # mass ratio 1.3:0.7
Eccentricity 0.19
Inclination 82.22
AscendingNode 67.30
ArgOfPericenter 184.02
MeanAnomaly 200.13
}
}
Barycenter "TridentSystemSchatGnom:Shattenmann and Gnomida"
{
OrbitBarycenter "TridentSystemHub"

EllipticalOrbit {
Period 3455.2506
SemiMajorAxis 208.00 # mass ratio 2:1.4
Eccentricity 0.02
Inclination 96.2
AscendingNode 133.5
ArgOfPericenter 256.4
MeanAnomaly 241.7
}
}
999997 "Schattenmann" # Schattenmann
{
OrbitBarycenter "TridentSystemSchatGnom"
SpectralType "DA2"
AppMag 17.055

EllipticalOrbit {
Period 700.85
SemiMajorAxis 34.00 # mass ratio 1:0.4
Eccentricity 0.19
Inclination 82.22
AscendingNode 67.30
ArgOfPericenter 184.02
MeanAnomaly 200.13
}
}
999996 "Gnomida" # Gnomida
{
OrbitBarycenter "TridentSystemSchatGnom"
SpectralType "M2V"
AppMag 15.825

EllipticalOrbit {
Period 700.85
SemiMajorAxis 85.00 # mass ratio 1:0.4
Eccentricity 0.19
Inclination 82.22
AscendingNode 67.30
ArgOfPericenter 4.02
MeanAnomaly 200.13
}
}

999995 "Simplicissimus" # Simplicissimus
{
OrbitBarycenter "TridentSystemMainSimp"
SpectralType "T0"
AppMag 24.025
Radius 99000

EllipticalOrbit {
Period 96.43
SemiMajorAxis 22.95
Eccentricity 0.01
Inclination 2.22
AscendingNode 67.30
ArgOfPericenter 4.02
MeanAnomaly 200.13
}
}



As you can see, it's definitely not Sol. Sol is 300 light years away. It's Trident and its companions that are drawn as big bright pennies, from any point at 1-10 ly away. It was not much of a problem while I was designing a single star system. But I tried to add a neighboring star at 3 ly distance - and it was visible from Trident as a honking big supergiant (and vice-versa, Trident and its companions were just as big from the other star). When I view stars as points, this effect does not manifest. I think that's the disc of the star that is drawn too large and bright.

[selden]

Could you upload a screengrab of what you see?
(Use F10 or Celestia's File menu, then the forum's Attach File option, which is below the text field where you enter a message.)

On my system there is an apparent brightening of your stellar system at about 1 LY which seems to correspond to the transition from drawing the stars individually to drawing them as a single light source. It's particularly noticeable when Scaled Discs is selected.

If this is what you're seeing, I'm afraid it has to be classified as a limitation of the current version of Celestia. Celestia draws a somewhat similar effect when transitioning from drawing a planet or moon's surface texture to drawing it as just a light source.

In principle, at least, if Celestia implemented HDRI effects, such transitional illumination effects could be minimized. Unfortunately, Celestia does not yet implement HDRI, just a crude representation of relative brightness, where the radius of a drawn object is proportional to its brightness.

Below is what I see. The left half of the display is from a distance of about 1.14 LY, the right from a distance of about 0.9 LY.

[aurora]

I guess it is really what I see, only on my system the embiggening effect is much stronger. In scaled disc mode, the stars appear like I'm damn close to Trident, inside the innermost planet's orbit. I'll post the screenshots when I'll make it to my home computer. I now realize the effect is inevitable, but how can I get it less drastic, like on your system? And why don't real stars demonstrate such a drastic embiggening effect?

[selden]

Remember I'm only guessing that this is the cause of what you see. It might be something else that I haven't found.

All of the Stars in Celestia's binary database are singles. They can't show the effect of multiple light sources merging to form one because they aren't multiple light sources. All of the Stars in Celestia which are multi-star systems are defined using STC files, just like yours except that they're in Celestia's data folder. They are all only doubles, though. (As best I can tell, no star systems included with Celestia have more than two components defined.) They should all show that same effect, but not as great, since they are only merging 2 stars instead of 3 or 4 stars to one point.

A major difference between your computer and mine is that yours has ATI graphics hardware and mine has Nvidia. Their OpenGL implementations are different, although I wouldn't have expected the display to very different for this. Please make sure you are running the current graphics drivers. They're updated almost monthly. They can be downloaded for free either from AMD's Web site or from the Web site of the manufacturer of your computer.

[selden]

Never mind.

My excuse for the brightening that I see was wrong. The brightening that I see is indeed visible for individual Stars on my system. It happens at 1LY from the Star. Any Star.

1LY is a "magical" distance in Celestia. It's the distance at which it stops drawing planetary systems defined by SSC catalogs and switches to drawing only the central Star(s). Apparently it affects how the Star is drawn, too. I'd have to consider this a bug, although drawing the Star small when closer does allow one to see planetary orbits more easily.

Here's the brightening that I see for Alpha Indi. (It was chosen arbitrarily. Celestia draws it as a single star without a planetary system. It's a 3 star system in reality, but the orbits are not sufficiently well known to be included with Celestia.)

[aurora]

Here are the screenshots. When I say huge, I really mean it! The captions in Russian say 0.95386 ly for the first picture and 1.1144 for the second one.

PS: AMD has long withdrawn any support for Mobility Radeon 9700 @ XP. Ditto for LG and LP60 notebook.

[selden]

What happens when you view HIP 2237 ?

That's the first of the double stars defined in Celestia's data\visualbins.stc

[aurora]

No funny effects at all. Celestia behaves as normal.