Celestia Forums

Hello everyone!

Although I'm not a programmer, I've been tinkering with the asterism.dat file and making improvements to how the constellations appear. Although that is irrelevant thanks to addons like this: http://celestiamotherlode.net/catalog/show_addon_details.php?addon_id=1524

I'm making this post because I have one question: Is it possible to make Constellations and Asterisms for other stars and planets? I'm eyeing for an Alpha Centauri Constellation map, because although from Alpha Centauri, most constellations still look the same, there's the case with Cassiopeia having 6 bright stars thanks to our Sun, and Sirius having a conjunction with Betelgeuse, ruining the look of Canis Major and Orion respectively.

Is there a way to do this or not?

Added after 8 minutes 49 seconds:
Correction:

Orion's look is actually not ruined by the Conjunction. On the contrary, Orion now has 3 1st magnitude stars, 2 of them marking the bright armpit of the Giant Hunter himself.



Added after 11 minutes 38 seconds:
And I forgot this mess too. This means Gemini has 2 1st-magnitude stars, and 2 2nd-magnitude stars as well

I'm not quite sure what you're asking.

As you've probably discovered, asterisms.dat just causes lines to be drawn in 3D between the specific stars listed in that file. The resulting constellations happen to look the way they do only because you're looking at them from our own solar system. As you've found, the constellations that those stars form look different when you look at them from another (nearby) star system.

If you want to create your own constellations as seen from another star system, you "just" have to create an asterisms.dat which lists the specific stars which make up those (different) constellations. In Celestia, you can then look at those constellations from any nearby star system and see how they are distorted.

A limitation in Celestia is that the interconnections specified in asterisms.dat are drawn only if you're within a particular distance from our Sun. Unfortunately, I don't recall what that distance is.

An alternative way to draw lines between stars is to create a CMOD model which draws those lines. CMODs can be used to draw lines between any of Celestia's xyz coordinates, and the resulting models can be seen from any viewpoint.

Some time ago I created a Lua .CELX Addon script which can be used to create an ASCII CMOD model which draws lines in any color you want between any pairs of stars, actually between any named objects known to Celestia. It's available at https://www.classe.cornell.edu/~seb/celestia/files/nroutes.zip (9 KB, expands to 19 KB)

selden wrote:A limitation in Celestia is that the interconnections specified in asterisms.dat are drawn only if you're within a particular distance from our Sun. Unfortunately, I don't recall what that distance is.

That's the problem I have in my Celestia 1.7.0. For 1.6.1, it's ok, because no matter which star system you go to, the lines remain. But the developers of 1.7.0 made the feature that you spoke of.

So, this is the Sun as seen from Earth, in Celestia 1.7.0:

The boundaries begin to disappear around 50-80 Au, as shown here:

Then at 1 to 2 ly, the constellation lines begin to disappear:


At 4 ly (Around the distance Alpha Centauri is from the Sun), the constellation lines are totally gone:


Actually, I think having multiple asterisms.dat files, at least for Celestia 1.7.0 won't be enough. I think what needs to be included is allowing objects other than Earth to have their own asterisms.dat. file. Like each file is specific to each object of the developer's choosing. If for example I want to create an asterisms.dat file for Proxima Centauri b, then the center focus of the asterisms.dat file should be Proxima Centauri b. And thus, the constellation lines and boundaries for Proxima Centauri b will only be seen if you're in the vicinity of the Proxima Centauri System. And if you leave the Proxima Centauri System, the constellation lines and boundaries associated with their respective files for Proxima Centauri b will disappear.

But I still trust your judgement. I'll try to do some experiments with the asterisms.dat file for my Celestia 1.7.0, and I'll see if having multiple asterism.dat files could actually work. After all, it's always good to test things out.

I have tinkered with this basic idea, but for a different purpose.
What I did was attempt to have celestia reload a new asterisms file anytime the observer got within a light day of a star.
I based it a star's HIP number, such as visiting polaris would see if asterism_11767.dat existed to be loaded.
That project got no further than dumping the current asterisms.dat db when clicking on a star with a mouse, and trying to load the new one.

Though I never finished, the basic idea might inspire a real programmer to go ahead.


Janus.

Janus wrote:I have tinkered with this basic idea, but for a different purpose.
What I did was attempt to have celestia reload a new asterisms file anytime the observer got within a light day of a star.
I based it a star's HIP number, such as visiting polaris would see if asterism_11767.dat existed to be loaded.
That project got no further than dumping the current asterisms.dat db when clicking on a star with a mouse, and trying to load the new one.

Though I never finished, the basic idea might inspire a real programmer to go ahead.


Janus.

Well, hopefully the developers of Celestia 1.7.0, particularly onetwothree can find a way to make that happen. And also allow for equatorial grids for all objects, because so far, only Earth's Equatorial Grid can be enabled. Having equatorial grids for other objects, especially exoplanets can enable me to determine which constellations are polar, equatorial or in between when making up fictional constellations and asterisms for exoplanets

The equatorial grids are going to be a problem.
To get those you need to know the north and south poles of stars, which includes knowing direction of rotation.
The least distant to a standard would probably be to use a galactic one generically, substituting a real one once it is known.
In fact, that could be an optional bit to add to the ssc, stc or other addon files.
Knowing when a planet transits a star does not guarantee knowing that solar system's ecliptic plane, only that it dimmed the star.
Even wobble detection only gives you a range, but not whether it is north or south.
The few that are image detected are not guaranteed to have circular orbits, so correcting for that is not guaranteed.


Janus.

Well, I'm pretty sure any Space Agency, especially NASA and ESA may have information on the North and South poles of most of the objects they recorded, from stars, planets, dwarf planets, asteroids and any other members of star systems. From there, it's up to a proper programmer to make a file including the equatorial grids of all those objects based from the information they got from any space agency.

But if any, I'd rather ask for the North and South poles of the planets, dwarf planets and exoplanets. As long as it's any circular object, it can be fine.

.
To determine the poles of objects, use the context menu. On the screenshot of Planet b stars Proxima Centauri:



For orientation of the north pole upwards, you can use the tool (see yellow oval) of the graphic interface Lua Universal Tools:

Croc wrote:To determine the poles of objects, use the context menu. On the screenshot of Planet b stars Proxima Centauri:




For orientation of the north pole upwards, you can use the tool (see yellow oval) of the graphic interface Lua Universal Tools:

Well, I know there's a feature to determine the poles of the planets. What's only left is just the Equatorial Grid.

#9by Lafuente_Astronomy » Today, 08:44

Well, I know there's a feature to determine the poles of the planets. What's only left is just the Equatorial Grid.

RA 217.428955° = 217.428955 / 360 * 24 = 14h 29m 43s