Celestia Forums

The manual for Celestia 1.32 says of the Star Filter/Faintest Star slider:

This slider determines how many stars Celestia will draw at one time. It regulates star number by how far away a star is from your viewpoint. By default, it is set at 1,000,000 light years. Since the diameter of our galaxy (the Milky Way) is about 100,000 LY across, Celestia will draw all stars in its data base at this slider setting. However, you can lower the slider and command Celestia to draw only closer stars. For example, if you set the slider to 100, the program will only draw stars that are within 100 light years of Earth.

However, it seems this "only draw so many stars a certain distance away" applies solely to whatever vantage point one is at. Which is good - for certain purposes (namely conserving processor power) but not so good for visualization purposes.

However, I thought it might be useful to be able to confine the Filter Star distances to Sol itself. So that I could tell Celestia to draw only the stars 100 light years away, but confine the "away" to an "away" from Sol. Since that confinement would be irrespective of my vantage point, I could then fly out and observe this "bubble" of stars around earth (similiar to what happens if you turn on the Constellation Boundaries and pull back very far).

This method has the advantage of being able to get a bird's eye view of how many stars are 10 light years from earth, then 50 light years... then see how the number grows when 100 light years from earth - and so on -- without being stuck INSIDE the bubble (which doesn't really give you a sense of it).

I love how Celestia allows user to get a "sense" of scale - and this feature would, I think, help. Often, when I'm showing new people Celestia and I pull back to reveal the stars they ask me, "Can you just show the stars that are 25 lights away" (and so on)... Of course, I CAN... but I have to be in that bubble now, which doesn't really give what they (and I) want.

GUI-wise, the simplest thing would be to add a "Confine This Filter To Sol" to the star fliter slider. Not sure what kind of code changes that would require.

Thanks,
Steven aka Blinded

Check out Mostly Harmless http://mostlyharmless.sourceforge.net/index.htm.

It'll do what you want, but not the way you think.

Thanks - but a few questions before I go digging:

1) It looks like Windows-only for the engine? True?
2) The other elements look like add-ons... which will just "add" to my star catalog... not limit it.

Or am I missing something?

Whoops, sorry. It is Windows only.

The version I downloaded did a completely separate install, but I've seen posts that suggest there's an add-on version that complements your existing Celestia installation.

There's a batch file in MH that generates imaginary planetary systems for the entire star catalog. It took 6 hours to run on my system, but every start has planets now. Kinda cool to go hunting for terrestial planets...

At the time its author disappeared (he went on walkabout and hasn't been heard from since), Mostly Harmless was a complete version of Celestia, not an Addon. The description is rather misleading in that respect. It includes an SQL Database implementation, which lets you select the stars that are to be shown by using SQL queries.

[edit]Do a search of the Celestia forum here. He made several postings displaying some of the features.[/edit]

selden wrote:(he went on walkabout and hasn't been heard from since)

lol... I like how you dropped in that cryptic and scary-sounding bit then jumped right into the SQL business...

Seriously, though - I hope everything is okay.

For all the coders reading this post, my guess is that Celestia handles the Filter Stars / Faintest Stars slider (which is it? the manual says Filter - my Mac version says Faintest) by some kind of subroutine that takes the viewers present location (I'm guessing an offset from Earth?) and only renders the stars that are a certain distance from that location. True?

And, if true, is it only a matter of telling that subroutine to NOT use the offset - and to use Earth's location as a "Only Render Stars From This Point" reference? That way - a bubble of stars can be seen around earth from any vantage point - per my initial post.

P.S. If anyone doubts to potential coolness of this - pull up the constellation boundaries marker and go 50 light years out... rotate around. Now imagine being able to do that with just the stars in our local region. And being able to say, "Hmm... now how many are THIS far out?" Then expand the bubble to see how many are THAT far out... and so on.

Gee, it didn't seem particularly cryptic to me, but maybe that's because I've seen too many movies that take place in Australia

"Walkabout" is a tradition that originated with the Australian aboriginees -- they renew their spiritual strength by leaving everything and travelling around the continent on foot. In this case, Marc seems to have used a vehicle, but I guess that's the modern equivalent. He posted a picture to the MH Web forum about a year ago showing one of his campsites, but hasn't posted anything since. See http://mostlyharmless.sourceforge.net/m ... c.php?t=87

selden wrote:Gee, it didn't seem particularly cryptic to me, but maybe that's because I've seen too many movies that take place in Australia

Awesome pic. Thanks. Though it wasn't the "going on the walkabout" that was cryptic... it was the "never came back" part...

IIRC the filter is based on brightness, not distance.

- Hank

hank wrote:IIRC the filter is based on brightness, not distance.

- Hank

Thanks, Hank. That's actually what I thought initially. After all, the slider is called "Faintest Stars" which is what initially made me think it was brightness-related, not distance related.

For clarification, before I go on: Is that, then, the same thing as the "Filter Stars" slider I referenced above and that is listed in the manual?

The manual talks about distance, not brightness. Are we talking about the same thing and the manual uses different terms? Or is there a difference between the Mac OS and other versions?

BlindedByTheLight wrote:

hank wrote:IIRC the filter is based on brightness, not distance.

- Hank

Thanks, Hank. That's actually what I thought initially. After all, the slider is called "Faintest Stars" which is what initially made me think it was brightness-related, not distance related.

For clarification, before I go on: Is that, then, the same thing as the "Filter Stars" slider I referenced above and that is listed in the manual?

The manual talks about distance, not brightness. Are we talking about the same thing and the manual uses different terms? Or is there a difference between the Mac OS and other versions?

I believe "Faintest Stars" is the same as "Stars Visible" in the manual. AFAIK "Filter Stars" is not implemented in Mac OS X Celestia.

- Hank

hank wrote:..."Filter Stars" is not implemented in Mac OS X Celestia....

Is the reason of this a coding problem or just lack of time for the port?

ElChristou wrote:

hank wrote:..."Filter Stars" is not implemented in Mac OS X Celestia....

Is the reason of this a coding problem or just lack of time for the port?

Actually, I think I just overlooked it. It shouldn't be hard to implement.

- Hank

hank wrote:Actually, I think I just overlooked it. It shouldn't be hard to implement.

- Hank

Yoo hoo!

Also, FYI - yep, the Faintest Stars slider in preferences is the Stars Visible function in the manual (just curious - how come there is a different name?) - however, the slider does not reflect the actual numeric value of the apparent magnitude of stars it will display.

What DOES display this number is using the keyboard (brackets) to control the same function. The reverse is not true -- using the brackets to change Apparent Magnitude does not update the slider position - which, technically, it should I think?

A minor tweak that I could really care less about - just throwing it out there. But that filter stars function... like I said:

Yoo hoo!