Celestia Forums

Here is my new add-on "Abell 39 (3D model)".

You can download it from my website :
http://membres.lycos.fr/tompouce00/



Enjoy and send me your comments.

For those who cannot download it, a mirror website will soon open.

AstroBoy

For the moment there's no central star because I couldn't find information about it...
If one of you could help me : I need the SpectralType and AppMag value.

AstroBoy

what is Abel 39?

Abell 39 is a planetary nebula. heres a quote

Abell 39, the 39th entry in a catalog of large nebulae discovered by George Abell in 1966, is a beautiful example of a planetary nebula. It was chosen for study by George Jacoby (WIYN Observatory), Gary Ferland (University of Kentucky), and Kirk Korista (Western Michigan University) because of its beautiful and rare spherical symmetry. This picture was taken at the WIYN Observatory's 3.5-m (138-inch) telescope at Kitt Peak National Observatory, Tucson, AZ, in 1997 through a blue-green filter that isolates the light emitted by oxygen atoms in the nebula at a wavelength of 500.7 nanometers. The nebula has a diameter of about five light-years, and the thickness of the spherical shell is about a third of a light-year. The nebula itself is roughly 7,000 light-years from Earth in the constellation Hercules.

AstroBoy,

Almost all central stars of planetary nebulae have just become White Dwarfs.

http://www.skyhound.com/sh/archive/jun/PK_47+42.1.html has some luminosity information. (I used Google to search for "abell 39 central star magnitude" I'm sure there are other pages with more details. This object has been studied quite a lot.)

Well I have added the central star a white dwarf and the nebula can now be seen from the inside...

Astroboy - I tried downloading some of your nebula models and I can't get them to work. I've got Celestia 1.3.0... does this require a later version of Celestia to work?

The 1.3.0 is the lastest version of celestia !!
I tested those nebula with 1.3.0 and 1.3.1pre3 and they work fine.

Dr. Ganymede,

Do you by any chance have one of the non-functioning protostar models installed? They'll block the view. (That happened to me just now by accident when I tried to reproduce your problem.)

Did you try a GoTo Abell 39 ?
Can you Select the object by typing its name?
(if not, then the DSC file is in the wrong place.)

Is it still invisible when you arrive?

What other symptoms do you (not) see?

For example, can you see its label appear when you toggle rendering of "Galaxy labels"?
After you've done a GoTo, can you see the central star but not the model?
Can you select the central star by typing
HIP 9000002
(that's 5 zeros between the 9 and the 2) ?

Can you see galaxies like M31 and the LMC?
(Remember that "galaxy rendering" has to be enabled for Nebulae to be drawn. Type a "u" to toggle rendering of "galaxies".)

Please be sure to include a description of your hardware and software configuration when you respond, as described in A2 of the "user's faq". You may have mentioned it before, but you might have upgraded since then for all we know.

I hope this helps.

Aha. Galaxy Rendering was turned off, that's why I couldn't see it. Now I have it - looks cool.

Though looking at the Astroboy's Ring Nebula, I notice it's rather flat. I thought it was supposed to be spherical, and the rainbow colours are coming from looking through the sides of the sphere?

Whew! that's a relief!

Ccelestia does not (yet?) support volumetric rendering, only suface rendering. In other words, you cannot define an arbitrary region with a smoky appearance that looks denser when you look through a greater thickness of material. (Celestia does have some internal routines to render galaxies which look sort of foggy, but they aren't really translucent. It'd be nice if they could be made more general.)

As a result, it's really hard right now to make an object that looks like a planetary nebula from all directions. You can't really make it look brighter around the edges from all viewpoints. I'm really impressed with how well Abell 39 turned out.

Because of this, most of the 3D nebular objects have been a type of "billboard". Some really are pictures posted on a flat object. There are those people who object to the fact that they're essentially invisible when seen from the side, though. Other models, like the one you mention, are pictures which have had stars removed and then have been projected onto a ripply surface. This has the advantage that they are visible, although distorted, from all directions.

Though looking at the Astroboy's Ring Nebula, I notice it's rather flat. I thought it was supposed to be spherical, and the rainbow colours are coming from looking through the sides of the sphere?

My philosophy is :

1st : the nebula must be photorealistic, in other word when see from earth, the nebula should be the same as the picture.
2nd : if possible try to represent the real 3D shape of it (when I can find it !!! There's no imaginary 3D model in my add-on)

As selden already told it celestia does not support volumic nebula, so the 2nd point can't always be made without make it ugly and unrealistic from other direction (like Helix). In such case I use projection on a ripply surface that I personnaly prefer to flat one (by the way, making it visible from the side).

By the way, there's a new version of the "Abell 39" nebula. Now outside of the nebula appear in front of the inside.

You can download it from my website :
http://membres.lycos.fr/tompouce00/