New star generator for other galaxies... (work in progress)

[Fenerit]

...
Or maybe add the spectral type in the name : "Fict O 23456", "Fict M 231456", "Fict G 437896", etc...

Such option is the best, in my opinion. For just one reason: should be very fast for anybody to know what spectral type is, how they "looks" and which are their propriety. For fictional planets' creators in search of a good place to live can help as well. Finally, Andromeda's constellations would have to be set, right?

[Cham]

Finally, Andromeda's constellations would have to be set, right?

Relative to which star ?

And there isn't enough stars to have a nice sky full of stars, except if I add a blurry ball of stars around a particular one (which I intend to do, since I already have an SF addon in the Andromeda galaxy, sitting there all alone !).

[Fenerit]

Therefore, one effectively will be forced into a 2-component approach, i.e. to render only a tiny portion of the whole galaxy in terms of say 50k stars when the observer is getting really close.

FYI, ... whilst once entered in it, "real" stars are good as well

~50k "real" Celestia stars for each small region of FoV would give a HUGE amount of STC data to read in altogether per galaxy! This is hardly practicable... If instead internal fake stars are used, they can be quickly generated and deleted from memory immediately after the screen-mapped FoV changed into another one (due to a moving observer).

The point is that the mapping of sprite-intensity to star coordinates is different for each small portion of FoV!

Fridger

Absolutely I agree with you about the "technical" parts. And what about your view concerning the fact that someone could wish to fly around a "real" star or to place an add-on on it? (this latter is not for you, but...) Few hundreds of stars should be handles well?

[Fenerit]

Finally, Andromeda's constellations would have to be set, right?

Relative to which star ?

And there isn't enough stars to have a nice sky full of stars, except if I add a blurry ball of stars around a particular one (which I intend to do, since I already have an SF addon in the Andromeda galaxy, sitting there all alone !).

Indeed. Even for this the second option is the better.

[t00fri]

Absolutely I agree with you about the "technical" parts. And what about your view concerning the fact that someone could wish to fly around a "real" star or to place an add-on on it? (this latter is not for you, but...) Few hundreds of stars should be handles well?

Well, then I only see the option to stick with a fast sprite rendering of galaxies throughout and insert a few "bulge" stars for hosting specific SF activities

Fridger

[Cham]

Well, then I only see the option to stick with a fast sprite rendering of galaxies throughout and insert a few "bulge" stars for hosting specific SF activities

Not just for SF activities. Stars also gives the sense of the vastness of space... (scale effect in Celestia).

I adjusted the HR distribution. I feel satisfied with it.

This is a small sample (1999 stars) from a set of 50 000 stars in M31 (so a sample of 4%, but the rest has the same statistical distribution) :

HR1.jpg

The STC file has a size of 7 MB. I don't notice any impact on the frame rate in Celestia, so all is fine (for me, at least). People should tell how many stars they want, before I release anything.

For comparison, here are four HR plots for other parts of my Celestia universe :

HR2.jpg

The upper-left shows our neighbors, for a sphere of 25 LY. The upper-right are all the default stars visible from Earth, up to apparent magnitude m = 5. The bottom-left are all the stars with exo-planets (from Grant's database), and the bottom-right diagram shows the stars from an old Rassilon addon (a star cluster). I think it's very instructive.

[t00fri]

How about looking at the real HR diagram for M31. It has been measured by the Hubble telescope and looks like so:

http://www.spacetelescope.org/static/ar ... o0315j.jpg

Fridger

[Cham]

How about looking at the real HR diagram for M31. It has been measured by the Hubble telescope and looks like so:

http://www.spacetelescope.org/static/ar ... o0315j.jpg

That plot isn't obvious at all (the axes are ambiguous). Can't do a comparison with it. And the title says it's all about the halo.

[ajtribick]

Looks like that's the HR diagram for the halo, the disc is probably going to be different because of differing star formation history...

[t00fri]

Here is the largest globular in M31, called G1. Also from the HST.



It's HR-diagram is also known

Fridger

[Cham]

Here's a preview of M31 with its 50 000 stars. Notice that all the labeled stars are just O1, O2, O3, ... (my brightness option is set to max). Of course, that's because they are the most luminous stars for this distance, and the population is all diluted (again, 50 000 stars "only", on the whole galaxy in Celestia). Unfortunately, the other stars aren't visible from almost any point (they are too diluted, so too far away), except in some cases here and there. This isn't a very bad state, since it helps to give the scale of things in Celestia. I think it's a very instructive feature (I may even use it in the classroom, actually).

M31a.jpg

Here's a point of view from my SF addon, sitting all alone in the middle of nowhere in M31 (about 2/3 of M31's radius) :

M31b.jpg

I'll add a blurry ball of stars, in a radius of 1000LY (it's so small, in M31 !), just to given their inhabitants a sky to watch !

EDIT : Another feature while traveling in M31 : it feels so "alien" out there ! I can't recognise any configuration, constellations, etc, as in the Milky Way.

[Cham]

If I desactivate the galaxy rendering, and change the stars aspect, I'm getting this (again, only O type stars are visible in this case) :

m31c.jpg

m31d.jpg

A random view with the galaxy rendering turned ON :

m31e.jpg

I think it's really pretty !

[Cham]

Wow ! With this star rendering (large blobs), it's really neat in there ! Too bad the other star type aren't really visible at this scale (they are much more numerous than the O stars. See again the HR diagram given on the previous page).

The view is from my SF addon (the yellowish star). This place really need a spherical distribution to cover the whole sky...

SF.jpg

What we see here is just a very small part of the whole distribution (50 000 stars in there).

[selden]

Don't forget that the density of stars in the disk is almost uniform. Spiral arms stand out because they contain bright, young stars, not because there are many more stars in them.

[Cham]

Just to add a comment :

M31's radius in Celestia is 70760 LY. Its thickness is about 5000 LY (roughly). Its volume divided by the number of stars (50 000) gives a mean spherical volume for each star (however, my distribution isn't exactly uniform, since the concentration is a bit higher near the central core, and lower near the edge). A simple calculation gives the mean distance between these stars :

More than 1400 LY between adjacent stars, on average ! OMG !

I intend to add a fuzzy ball of radius 5000 LY, containing 20 000 supplementary stars around the central core. This gives (very roughly) 370 LY between adjacent stars !

Talk about a low density !

[Cham]

I added a fuzzy oblate ball to the core, with an HR diagram gently shifted to the yellow-orange color (older stars). The ball contains 25 000 stars in a radius of roughly 6000 LY (the spheroid is oblate) and fits very well the central yellowish core of M31. The STC file is 3.6 MB.

So in total, there are 75k stars in M31 right now. This gives an average distance of roughly 650 LY between adjacent stars.

I'm cleaning both STC files and test them before releasing them on the forum.

[W0RLDBUILDER]

EDIT : Hmm, I just had this idea : "And G234567", "And M78321", "And O5643", "And K03456". This way, we know the star is in Andromeda, and we know it's spectral class before selecting it. Maybe adding an "f" at the end to tell it's a fictious star (or is it too cryptic ?) : "And G21345f"

That's the best idea IMO. Maybe something like M31-G2V-3215f. I don't like the idea of putting Fict in front of everything. IMO it's like blurting out in the middle of a play "THESE GUYS ARE JUST ACTORS!!!".

[Cham]

Here are two STC files to test.

The first file places 50 000 stars everywhere in M31 with a slight increase in density near the central core. The second file places 25 000 stars in the galactic core (some K stars are very big there). The user can easily edit the files to change the star name prefix to his/her taste ("And", "And_C" for Andromeda and Andromeda_Core, so its easy to find in Celestia). Note that the spectral type is given in the name (letter O, B, A, F, G, K, M, followed by a first digit. Other digits are just random crap).

http://fsgregs.startlogic.com/Public_Fi ... 1stars.zip (2.2 MB)

To see more easily some parts of the distribution, I suggest that you use the scaled-disk option for the stars rendering. However, don't forget that you'll only see the more luminous stars (mostly blue O type). Most stars aren't visible at all if you're too far away.

Also, keep in mind that 75 000 stars scattered in a large spiral galaxy of the size of M31 is really poor, so stars density is extremely low (about typically 700 LY between adjacent stars, on average).

The stars labels are behaving very well, even when the star brightness rendering is pushed to the max (thanks to the low density of stars !). Try also turning OFF the galaxy rendering... To find any G2 stars, just type "And G2..." or "And_C G2..." in Celestia.

Please, I need feedback to improve that stuff. Any crittics, suggestions, comments ?

Let me know if you ever find some weirdness...

[Hungry4info]

The only thing I really noticed was the rather high values for the radii and luminosity of main sequence stars, but of course you can't otherwise see them.

How far do you think you could go as far as star count?

[Cham]

The only thing I really noticed was the rather high values for the radii and luminosity of main sequence stars, but of course you can't otherwise see them.

? Can you elaborate on this ? Some stars are unrealistic ? In the core, there are some stars which are out of the main sequence (a few giant K). Other than a few of them, they should all be main sequence.

How far do you think you could go as far as star count?

The only limit is Celestia. Too much stars will impact the frame rate. I can generate a file of one million of stars, but I don't see much the usefullness and the STC file would be huge (about 100 MB ?).