Adding stars

[chris]

It's nice to be able to add stars, but it would be nicer to be able to add them just like planets. The orbital parameters of certain double systems are known. That would be spectacular!

Greetings.

Bruckner

I am thinking since quite some time whether it is not time again for us "Perl-addicts" to scan the Washington double star catalog in order to extract the missing partners and their orbital parameters as far as they are known;-)

Bye Fridger

If someone can get the data, I can modify Celestia to handle multiple star systems. I've thought it through pretty well, I think. Eclipse shadows in a binary system are going to be tricky, though. Also, I've been working on comets lately and was wondering what a comet in a binary system would look like. Let's say it approached within 1 au of components separated by 0.5 au. Are there two tails? Two ion tails and a single dust tail? Anyone care to speculate?

--Chris

[Rassilon]

I think maybe two tails...since the shadows are doubled...I would gather glares would be as well as comet tails...

It would be nice to include additional names for the star in the *.stc file. Possible?

Add them in starnames.dat seperated by colons...

[Vicware]

Maybe Chris you should turn off eclipses while outside our solar
system. I'm not sure that seeing one binary star casting a shadow
on another is worth the trouble. Unless there are planets orbiting,
which I guess they're finding more and more.

My greatest wishes are still the same:

1.Some kind of color and shading to the galaxy, with a bright center.
2.Random mapping of stars w/spots. If I had time I would create several
maps for stars. I've been trying to think of a way to show prominences
and fountains using 3d model for a star.

Vic

[t00fri]

If someone can get the data, I can modify Celestia to handle multiple star systems. I've thought it through pretty well, I think. Eclipse shadows in a binary system are going to be tricky, though. Also, I've been working on comets lately and was wondering what a comet in a binary system would look like. Let's say it approached within 1 au of components separated by 0.5 au. Are there two tails? Two ion tails and a single dust tail? Anyone care to speculate?

--Chris

Here are the data columns of the Washington Double star catalog. Which ones do we want?

Byte-by-byte Description of file: catalog.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh *Right Ascension 2000 (hours)
3- 5 I3 0.1min RAdm *Right Ascension 2000 (minutes)
6 A1 --- DE- *Declination 2000 (sign)
7- 8 I2 deg DEd *Declination 2000 (degrees)
9- 10 I2 arcmin DEm *Declination 2000 (minutes)
11- 17 A7 --- DiscName *Discoverer Code & Number
18- 22 A5 --- Comp *Component Identification
24- 26 I3 a Date1 ?Date of first satisfactory
observation (+1000)
27- 29 I3 a Date2 ?Date of last satisfactory
observation (+1000)
30- 31 I2 --- NumObs *?Number of measures of the object
32- 34 A3 deg pa1 *Position Angle for Date1
35- 37 A3 deg pa2 *Position Angle for Date2
38- 42 F5.1 arcsec Sep1 *?Angular Separation for Date1
43- 47 F5.1 arcsec Sep2 *?Angular Separation for Date2
48- 52 F5.2 mag MagA ?Magnitude of component 1
53- 57 F5.2 mag MagB ?Magnitude of component 2
58- 66 A9 --- Sp *Spectral Types of Primary/Secondary
67- 70 I4 mas/a pmRA *?Proper Motion in Right Ascension
71- 74 I4 mas/a pmDE *?Proper Motion in Declination
75- 82 A8 --- DM *Durchmusterung Zone & Number
83- 84 A2 --- note *Notes
-------------------------------------------------------------------------------

Bye Fridger

[bruckner]

I've found a catalog more suitable for direct data extraction: the Sixth Catalog of Orbits of Visual Binary Stars. It's available here: http://ad.usno.navy.mil/wds/orb6.html

There are orbital elements for 1660 stellar systems (majority of double ones, but also multiples) in the same format planetary orbits could be given. An easy way to recreate those stars in Celestia would be to use a ssc format similar to the one used for planets. This is a proposal:

"Secondary star" "Primary star"
{
Class "star"
[... other data, like magnitude, spectral type...]
[... size and mass may be estimated from these...]

EllipticalOrbit
{
[... same data as for planets...]
}
}

The difficulty I envision: most of those stars are already in the Hipparcos catalog, and thus reflected in Celestia as "static" stars. Precedence should be given to this definition, ignoring the static data in stars.dat. Other than this, I think we could extract/estimate the rest of the data.

I don't think double shades and double tails would be too much of a concern right now: it's better to have double stars now and worry about details later. As the old Spanish adage says: "M?s vale p?jaro en mano que ciento volando" ("a bird in hand is preferrable to a hundred flying birds", oh, my, this translation sounds silly )

BTW: there are also catalogs for cepheids. Would that be too much to ask for...?

Greetings.

Bruckner

[Rassilon]

Don't forget to add in the ability to modify emissive specular color, flare color, texture and clouds...Clouds would be used mainly for appearence...If left out it would default to the spectural type...

Also there is rings...When giving a star a dust ring or accretion disk for neutron stars and black holes...the shadow should not be there for emissive objects...

This would give more variance to the look of stars...but yet tis still not so important I guess...*crosses fingers* Hopefully it will not be deemed so

[t00fri]

As the old Spanish adage says: "M?s vale p?jaro en mano que ciento volando" ("a bird in hand is preferrable to a hundred flying birds", oh, my, this translation sounds silly :D )

Greetings.

Bruckner

Since this forum represents a multi-cultural "conglomerate", it may be fun recalling some further versions of this well known proverb:

In English, I think it reads:

"A bird in the hand is worth two in the bush".

The literal translation of the German version is still different:

"A sparrow in the hand is worth more than a pigeon on the roof"

So, who knows the Japanese version of it ??;-) Sum0 where are you?

Bye Fridger

[Pixel]

..adages..

A similar one in bulgarian is awfully translated as:
-don't leave your domestic animals only for purpose to catch wild one.
or:
-never quit certainty for a hope
or:
-dont't throw away/ drop the substance for the shadow

But i don't like them - aren't they progressless statements?

i am really interested in japanese versions. And i am a big fan of haiku

[Marg]

In latvian:
"Labāk zīle rokā nekā mednis kokā"
which means
"better acorn in the hand than capercailye on the tree"

[Marg]

Ooh, special latvian diacritic signs cannot be seen...
"labak zile roka neka mednis koka" it`s more similar.

[chris]

I've found a catalog more suitable for direct data extraction: the Sixth Catalog of Orbits of Visual Binary Stars. It's available here: http://ad.usno.navy.mil/wds/orb6.html

There are orbital elements for 1660 stellar systems (majority of double ones, but also multiples) in the same format planetary orbits could be given. An easy way to recreate those stars in Celestia would be to use a ssc format similar to the one used for planets. This is a proposal:

"Secondary star" "Primary star"
{
Class "star"
[... other data, like magnitude, spectral type...]
[... size and mass may be estimated from these...]

EllipticalOrbit
{
[... same data as for planets...]
}
}

The difficulty I envision: most of those stars are already in the Hipparcos catalog, and thus reflected in Celestia as "static" stars. Precedence should be given to this definition, ignoring the static data in stars.dat. Other than this, I think we could extract/estimate the rest of the data.

Merging the data with the Hipparcos catalog is definitely an issue. But the main thing is that all the code in Celestia currently assumes that the position of a star is static. I'll have to change quite a bit of code to get multiple star systems working properly. The problem is surmountable, but it will take a good amount of work.

I don't think double shades and double tails would be too much of a concern right now: it's better to have double stars now and worry about details later. As the old Spanish adage says: "M?s vale p?jaro en mano que ciento volando" ("a bird in hand is preferrable to a hundred flying birds", oh, my, this translation sounds silly )

I was mostly kidding about the double comet tail question, though it is interesting to speculate about it. Also, the stars in visual binaries are separated by enough distance that for purposes of lighting an orbiting planet, the light from one star will be much greater than the light from the other, so for a reasonable approximation, Celestia can just use a single light source.

BTW: there are also catalogs for cepheids. Would that be too much to ask for...?

This is somewhat easier than multiple star systems. How big is the catalog?

--Chris

[t00fri]

The difficulty I envision: most of those stars are already in the Hipparcos catalog, and thus reflected in Celestia as "static" stars. Precedence should be given to this definition, ignoring the static data in stars.dat. Other than this, I think we could extract/estimate the rest of the data.

Merging the data with the Hipparcos catalog is definitely an issue. But the main thing is that all the code in Celestia currently assumes that the position of a star is static. I'll have to change quite a bit of code to get multiple star systems working properly. The problem is surmountable, but it will take a good amount of work.
--Chris

This problem of eliminating multiple entries in the star data base coming from /several/ catalogs and typically involving slightly different RA,DEC values is quite generic and should be generally solved before Celestia is ready for multiple catalog entries. The way this has been solved before is by means of a "search, compare (RA,DEC, names) and eliminate" algorithm within a given range around a given star. It only has to be done once at the beginning when the catalogs are loaded. During the extraction of double stars by means of Perl, I would also have the HIP... file open in parallel for cross-checking and selecting the "partners".

After my work on the AutoMag feature, I am more than ever convinced that the addition of weak stars would make an /essential/ optical /and/ "scientific" enhancement. I also hope that the AutoMag may represent a bypass of the fact that these star bases like Hubble GSC a lacking certain info that Celestia in principle requires. With AutoMag, these weak stars would only be needed at /very small fields of view/ that effectively reduce the problem to a more conventional 2D starmapping one....

Bye Fridger

[Rassilon]

I know the old addege 'Cross that bridge when we get to it' but when the time comes to add stars to fill the galaxies...how were you thinking of doing this? Random seed like Sirius? Of course I don't know for sure...but I doubt there is a catalog with all those stars plotted...

Or is this going to be complicated by the idea of preserving Celestia's realism due to the fact that its main focus is that very thing...

If you add such a thing maybe having a way to disable it...including addons...

[t00fri]

thinking of doing this? Random seed like Sirius? Of course I don't know for sure...but I doubt there is a catalog with all those stars plotted...

Or is this going to be complicated by the idea of preserving Celestia's realism due to the fact that its main focus is that very thing...

If you add such a thing maybe having a way to disable it...including addons...

There are catalogs that contain quite faint stars: The Hubble guide star catalogue (GSC) has stars up to including m = 16! Tycho2 is going also much higher than HIP...
However certainly not the stars of galaxies. For globular clusters, there are already quite a few visible...

The complete GSC data is about 180MB just like a decent earth texture;-)...

Yes, the AutoMag = " auto faintest star magnitude adaptation to the field of view" feature may be switched off. Also there must eventually be a dialog that allows to select, load and delete individual star data sets.

With enough faint stars, AutoMag gives a great plastic feeling when you zoom into small fields of view or out again: lots of stars are moving out of the window when the angle gets smaller, but many new, fainter ones appear like in a telescope when you increase the magnification. The advantage is that you need to render those faint stars only when the field is small...and it looks great;-)

Years ago I derived the theory for all this, when we incorporated the AutoMag into XEphem. There is also a switch for turning it off, but people tend to leave it always on.

Bye Fridger

[dtessman]

If someone wants to tell me what exactly is the format of stars.dat I will throw together some Java code to munge it into and out of an XML document.

[Rassilon]

Its already posted earlier in the thread...

[dtessman]

Its already posted earlier in the thread...

Yup! oh dopey me...

If I wanted to convert parallax seconds to lightyears (and back again), how does parallax error fit into the formula?

Any other requests for formatting the XML would be welcome. I figured it would export/import in a "native" as well as "preferred" format. For instance does it make sense to use absolute maginitude and color index instead of apparent mag and type?

[dtessman]

CStarsConv is a windows application that converts the stars.dat database to XML and back again. The exe and complete source code is available from SpaceGear.Org.

[Mutos]

Hi everybody,


Just read all the thread (that long ! & i'm still adding to it ^-^) ! It covers some questions i asked in another thread & didn't find answer...

Would be Very Very Nice to be able to add a star name w/o tweaking starname.dat, like for instance in stc files. Think of all of us sci-fi creators trying to name explored systems - lol !

Btw, is there a comprehensive Celestia doc somewhere ? I just have so many questions the forums won't be enough !

Beno?t 'Mutos' ROBIN
http://hoshikaze.net

[Rassilon]

Chris is adding that in 1.2.5...

The only documentation so far is a brief manual and whats included in the download...Also a script reference on the main page