Celestia Forums

Imagine if you will a quaint double star system in a region of the Universe near Orion.

Imagine that the primary was a young B6 V star with an absolute magnitude of -0.61. Imagine also that the secondary was a relatively young red dwarf of class M4 V and an absolute magnitude of 11.92.

Now, imagine that these stars were seperated on average by a distance of just .06324038 AU, or roughly 9,460,626 kilometers. Because Celestia doesn't do binaries the orbital data is irrelivant.

Now consider in this increasingly hypothetical binary system, that a lone planet was placed in the confort zone around the primary. This orbit would have a semimajor axis of 12.20046 AU, with negligable eccentricity, and a period of about 42 years. Now said planet would orbit happilly about the two stars if it were not for one horrifying detail. This arangement results in Celestia making said planet invisible!

When I placed a planet around the secondary, celestia had no problems, it was illumnated red, and no attention was paid to the looming Blue Giant in the distance. However I think I "broke" Celestia when I decided to have the planet orbit BOTH stars.

As I've heard Celestia can only deal with one light source at a time, and a planet in orbit around two stars would have to deal with two light sources. In any event I think this is why my planet is physically there, but invisible. Can anything be done about this?

Cheers.[/img]

Apollo7,

Since Celestia really doesn't do planetary systems with multiple stars, a planet can only be seen when you're in the solar system of the star that it's orbiting. Celestia does not currently "understand" that stars can be so close to one another. Going to one star means that the planets orbiting the other one are not drawn.

As a result, people have created multiple star systems by defining fake planets which have the charactistic "Emissive true" as standins for stars other than the one being used as the primary.

I hope this clarifies things a little.

Indeed I Have heard of the "Emissive true" option, however, from what I've seen such "stand ins" look nothing like the stars they are to repalce. Also since I have a poor understanding of some of the finer details of Celestia I'm not sure exactly how I would pull off such a thing.

It makes no sense to have a "planet" stand in for a "white dwarf" when you can not see said "white dwarf" from .1 AU away. Perhaps you can clear this up for me, if the work around for Emissive True works I'd definately want to give it a shot.

The appearance of an object is determined by the designer. Some are better than others.

Until Celestia can directly support multiple stars orbiting around a common barycenter, we have to make do with the tools that are available.

There are several documents on the Web describing the various declarations one can use in an SSC file.
I'd suggest looking at one of Rassilon's projects to see how they can be used.
His NGC1999 add-on is one example.
In order to increase the distance at which a "planet" is viaible, one can specify a non-physical albedo: e.g. 1e6

I hope this helps a little.

... Selden (using a not-logged-in Lynx session)

selden wrote:Apollo7,

Since Celestia really doesn't do planetary systems with multiple stars, a planet can only be seen when you're in the solar system of the star that it's orbiting. Celestia does not currently "understand" that stars can be so close to one another. Going to one star means that the planets orbiting the other one are not drawn.

This is actually pretty easy to fix . . . I'll try and get it into 1.3.1. Multiple light sources will take a bit more time, however.

--Chris

Well I'll say this: it is more important to have working/functional binary star systems than to worry about the eye candy of double light sources. Realism can be an adequate replacement for visual luster. Once binary stars are officially possible. Other people can go in and start adding them to the systems currently lacking. It would be nice to see Capella as it is for example. In any event I digress. In my case my planet "Eden" is visible from about 12 AU away, it is only when you zoom in that it becomes invisible. Which is why I called it the "disapearing planet"

I mentioned elsewhere that the radii were being underreported in Celestia, this is half true however during this experiment I checked out a few things and heres some of the evidence:

Star, Lachesis (S2-PS): G9V, Expected Radius .71, Reported Radius: .70, Absolute Mag 5.95
Star, Clotho (S3-PS): M4V, Expected Radius .22, Reporeted Radius: .12, Absolute Mag 11.92
Star, Atropos (S4-PS): B6V, Expected Radius 3.3, Reporeted Radius: 2.15, Absolute Mag -0.61

All three stars are roughly 45 light years distant from Earth. Clotho Orbits Atropos, and Lachesis is some .226 light years distant from the pair.

What gets me here is how far off the radii was for Clotho and Atropos, but how close it was for Lachesis.

For example the reported Radius for Atropos is off by 34.8% (thats a lot). I use a program called HR Calc to give me some basic data for the stars I create, you guys should check it out, its shareware and very usefull. Anyway: any of you know why stars nearer to the sun in classification get a break on the radii reporting problem?

Also when you have two stars very close together, will it take multiple light sources to have Celestia report the COMBINED apparent magnitude of the two stars? Cheers.

Apollo7 wrote:Well I'll say this: it is more important to have working/functional binary star systems than to worry about the eye candy of double light sources. Realism can be an adequate replacement for visual luster. Once binary stars are officially possible. Other people can go in and start adding them to the systems currently lacking. It would be nice to see Capella as it is for example. In any event I digress. In my case my planet "Eden" is visible from about 12 AU away, it is only when you zoom in that it becomes invisible. Which is why I called it the "disapearing planet"

Mail me your add-on (claurel@shatters.net) or post it here, and I'll try and fix the disappearing planet problem.

I mentioned elsewhere that the radii were being underreported in Celestia, this is half true however during this experiment I checked out a few things and heres some of the evidence:

Star, Lachesis (S2-PS): G9V, Expected Radius .71, Reported Radius: .70, Absolute Mag 5.95
Star, Clotho (S3-PS): M4V, Expected Radius .22, Reporeted Radius: .12, Absolute Mag 11.92
Star, Atropos (S4-PS): B6V, Expected Radius 3.3, Reporeted Radius: 2.15, Absolute Mag -0.61

All three stars are roughly 45 light years distant from Earth. Clotho Orbits Atropos, and Lachesis is some .226 light years distant from the pair.

What gets me here is how far off the radii was for Clotho and Atropos, but how close it was for Lachesis.

For example the reported Radius for Atropos is off by 34.8% (thats a lot). I use a program called HR Calc to give me some basic data for the stars I create, you guys should check it out, its shareware and very usefull. Anyway: any of you know why stars nearer to the sun in classification get a break on the radii reporting problem?

The problem is that Celestia 1.3.0 uses the absolute magnitude in the visible spectrum to copute stellar radii. G class stars emit most of their energy at these wavelengths, so it follows that the size reported by Celestia is close to the expected value. But M and B stars emit a lot of energy in the infrared and ultraviolet, respectively . . . The radius estimate will not be accurate unless this is taken into account. Yesterday, thanks to a suggestion from Grant, I fixed the problem. Now, the absolute visual magnitude and spectral class are used to estimate the bolometric magnitude (which considers the entire spectrum), and this value is then used as an input to the calculation for radius. With the new code, the size of Proxima Centauri went from 0.02 to 0.08 solar radii.

--Chris

Thanks for the reply Chris, yes other people have been telling me this but I wasn't able to wrap my head around it until now. Indeed, with cool dim stars theres alot of radiation thats outside of our visual range, a similar effect plagues hotter more brilliant stars. This is why an exceptional star like say, Saiph in Orion, doesn't appear all that brilliant to our eyes, much of its radiance is in UV.

So that all makes sense to me now. My add on such as it is includes real stars too like Ross 248, EG 290 (a white dwarf) and Wolf 424. I had to remove YZ Ceti as it is in fact included in the original Celestia distribution. I want to add a few more nearby dim stars. Oppenheimer has a Catalogue of the nearest stars to 8 parsecs which is quite usefull. I believe it was published in 2001 and has some very accurate parallax measurements.

if I can just solve the little distance problem I've been having, I'll go through Oppenheimers list and add all the stars which are currently missing from Celestia. I got CStarsConv to give me the data for Sirius, and using the provided RA, Dec, and Distance I tried to place Sirius B, unfortunately even using the data that Celestia uses Sirius B is still off by about 11 AU. I don't see how this is possible but the numbers don't lie, its a bizzare situation, I'll include Sirius B (using Celestia's internal data) to illustrate if you wish.

Cheers.