Preview: Ran: The Billow Maidens II

[Evil Dr Ganymede]

Nebulae are extended light sources, and they don't get any brighter, area for area as you approach them. Twice as close, four times as bright, but also four times the angular area. (In fact, Phil Plait says here that optically thin nebulae will become less visible as you approach, something I've never quite got my head around.)
Anyway, best case scenario is no increase in surface brightness. And we know the Trifid Nebula is invisible to the naked eye at night on Earth ... it's magnitude 9, with that light smeared over a spot of light almost as big as the full moon. If you got up close, all you'd see was a heck of a lot of magnitude-9 moonsized patches side by side ... ie, nothing at all, even at night with dark-adaptation.

Gnyaaar . That's a really interesting article...! But there are bits of shocked gas in the Triffid nebula surely? Wouldn't the bright patch where the dark lanes cross be more visible?

[granthutchison]

But there are bits of shocked gas in the Triffid nebula surely?

I dunno. Anyway, all I'm saying is that "The Trifid Nebula" as the object we recognize in photographs cannot be perceived by the naked human eye, no matter how close to it you get. Seeing some strands of light in the sky is rather different experience (though no doubt lovely), and Plait unfortunately (and uncharacteristically) provides no information about the brightness or density of these things.

Wouldn't the bright patch where the dark lanes cross be more visible?

Magnitude 9 over the area of a whole full moon is bloody dim ... you're talking the equivalent of a magnitude 16 star. That little central area would have to be ten thousand times brighter than the surrounding nebula to be even marginally visible after dark adaptation at night. It would surely be a bit overstaturated in photographs of the Trifid if it really were that much brighter than the rest.

Grant

[rthorvald]

Will the final realization included a historic summary of this universe? I've used the chronology to present various stages and screenshots in the pages of my catalog

Yes, i will include an updated chronology. I?m a bit undecided on CelUrls, though, as it has been discovered that there are incompabilities between OSX1.3.1 and the various 1.3.2 implementations - i can?t make urls that will work on the later Win 1.3.2 builds.

-rthorvald

[selden]

Do the older .CEL scripts work with the Mac version of Celestia? If so, their GOTO commands might be a workaround for the positioning problems of Cel:// URLs.

[granthutchison]

(In fact, Phil Plait says here that optically thin nebulae will become less visible as you approach, something I've never quite got my head around.)

Aha.
Revisiting this topic prompted me to think about it some more, and I've finally got it, by coming at it from a ray-tracing perspective.
If you look at an optically thick nebula, then every line of sight from your eye to the nebula will eventually be intercepted by a hydrogen atom (or some other item of gas or dust; it doesn't change the reasoning). Whether you see a photon coming down that line of sight at any given moment will depend on the precise nature of the nebula, but there is always the potential for something to come your way. The cumulative effect of photons zinging intermittently down all these sight-lines creates the sensation of brightness at your eye. If you move closer to the nebula, more sight-lines open up, but all these sight-lines are similarly intercepted by hydrogen, in pretty much the same state of excitation as you were seeing previously ... so the surface brightness of the nebula doesn't change as you move closer, it just grows larger in your field of view.
However, if you're looking at an optically thin nebula, many of your sight-lines pass right through and out the other side, to the blackness of space beyond. Moving towards this nebula opens up more sight-lines, too, but almost all of them end in black space, instead of encountering new hydrogen atoms deeper in the nebula. The nebula grows larger in your field of view, but the total amount of light that reaches your eye stays almost exactly the same. So the closer you get, the lower the surface brightness gets, until the nebula becomes invisible.

Grant

[Evil Dr Ganymede]

So what are examples of optically-thick nebulae?

[granthutchison]

So what are examples of optically-thick nebulae?

I haven't a scooby.
Googling "optically thick nebulae" reveals a scatter of papers, but nothing that looks like it might produce a list. (I confess I didn't try any of the links.)

Grant

[selden]

Hmmm....

Aren't most of the visible nebulae "optically thick", at least in visible wavelengths?

Certainly the dark dust clouds in front of many of them are opaque, and many active star forming regions have lots of stars that are detectable only in the infrared because visible light can't get through the clouds between them and us.

[Jeam Tag]

I?m a bit undecided on CelUrls, though, as it has been discovered that there are incompabilities between OSX1.3.1 and the various 1.3.2 implementations

Hi Runar, thanks. Later, it would be interesting to have a script, like tv documentary wich summarizes the different stages of the exploration and exploitation of the system
But, first, we want to play with your great improvements

[rthorvald]

Well, Ran II is more or less completed. Has been for a little while, in fact... Currently, i am trying to scale it down to something that is manageable - i could easily publish a gigabyte here, and i don?t think that is practical. I hope to get it down to about 600 mb, by cleaning out less important hi-res files, and omitting a few scenes that does not really deepen the scenario much.

The huge filesize is due to several things: more elaborate modelling, deeper VTs, and several new locations. But i?m afraid i have been thinking more about building it than making it easy to distribute.

Here?s some new screenshots:






-rthorvald

[Guest]

Good grief...stunning images!

Regards...bh.

[Jeam Tag]

Well, Ran II is more or less completed. [...]The huge filesize is due to several things: more elaborate modelling, deeper VTs, and several new locations. But i?m afraid i have been thinking more about building it than making it easy to distribute.

Superb!
To distribute, you can organize different packs (planet by planet, or basic pack to install first and VT and hires in another packs, for example) that can be unzipped in the same extras/fictions/BillowMaidens Folder, like the numberous B5 addons by BCelestia or the Star Trek addons (medres and hires) by Jestr, can't you? If the hierarchy of the different files and folders is the same in each packs, the different elements will take place in the right places. Jeam.
Again, this Universe looks really fabulous.

[rthorvald]

To distribute, you can organize different packs (planet by planet, or basic pack to install first and VT and hires in another packs, for example) that can be unzipped in the same extras/fictions/BillowMaidens Folder

Hm... I was thinking of splitting it into 3 separate downloads:
1) The Solar System, in lores+medres
2) The HiRes folder for 1)
3) The Civilisation: this would work as an entirely separate add-on in it?s own directory, and would add all the spacecraft and stuff to the solar system.

Doing it this way would allow people to choose if they just wanted the worlds, or both the worlds and their history - at the resolution of their choosing. But each download will still be big - about 120 MB for 1 and 3, maybe twice that for the HiRes folder...

Still, is this preferable to the planet-by-planet model? It?s certainly easier.

-rthorvald

[Jeam Tag]

Still, is this preferable to the planet-by-planet model? It?s certainly easier.

Honestly, I don't know, Runar: it depends of the organization/priorities you use for your Ran Universe. I've just suggested many ways to split big packs like other were are online, based of the first Ran release, for example. Your choice sounds good and useful, seems to me that the main install (planets -lores and medres) must be a first pack, all Hires, VT second ones, all artifacts and/or 3d tiles other ones, etc... I don't know exactly because I do not have your work installed!, but it seems to me that the more simple install for addons in Celestia, now, offers many ways to purpose very big ones.
Hope you find a way to split and share your work in a way that all the people can dwl and run, I do not speaking just about me! Jeam

[TERRIER]

Hm... I was thinking of splitting it into 3 separate downloads:
1) The Solar System, in lores+medres
2) The HiRes folder for 1)
3) The Civilisation: this would work as an entirely separate add-on in it?s own directory, and would add all the spacecraft and stuff to the solar system......

Runar,
Personally, I'd like to see it packaged like this. The HiRes folder could be treated as an "optional extra". I think it's best to keep the solar system together. Having all the planets as smaller separate downloads could possibly lead to lost files and installation errors.
But then again, it's easy for me to say this, with having a broadband connection.

Also was wondering if you've decided not be release all of your high detailed textures and models for this add-on, because of the final file size ?
If so, then maybe these could be "optional-optional extras" !!!, after all, what is the harm in another gigabyte?

cheers,
TERRIER

[rthorvald]

Personally, I'd like to see it packaged like this. The HiRes folder could be treated as an "optional extra". I think it's best to keep the solar system together

I will go for that solution. Three separate downloads, where the medres/lores (about 110mb) solar system can work as a stand-alone.

Also was wondering if you've decided not be release all of your high detailed textures and models for this add-on, because of the final file size ?

Yes, i?m leaving out some VTs that i don?t feel add much to the experience - like the ones where there?s nothing much to zoom in on, or hi-res versions of the shorter, intermediate phases of the terrestrial planets. That will save 200-300MB, so it?s worth it.

If there?s interest, i might zip them up as an "extra" as you suggest, after publishing the add-on.

-rthorvald