Celestia Forums

Hi all,

I cannot understand how I didn't notice this earlier: in Celestia all spiral galaxies, as seen from ours, have their arms unfolding in a clockwise direction. Well, I didn't check all of them, but I checked several that should be counter-clockwise, and they are not: M 33, M 611, M 83, M 74, M 99, NGC 2207 (today's APOD, the one that made me look at it).....

Is this by design? Is it for lack of the corresponding data in the catalogs from where the new galaxies have been extracted?

Moreover: would it be sensible to correct this, even manually, at least for the brightest galaxies of known orientation?

I can't recall reading about this when Fridger prepared the current catalog. I have been searching the posts without results, also. If it is something that has been dealt with, forgive me. It just seemed strange to see M 33 or M 74 "from the wrong side"...

Regards,

Guillermo

Guillermo, Fridger should respond here, but I'm sure it's a question of missing data in catalogues. Now actually one can open the png files used to describe the types, invert them, saves them as XXX_CC.png (CC for counter-clockwise for example) and assign the new templates to the concerned object by using the CustomTemplate definition...

Yes, I guess so. I wonder if it can be done transforming the Axis property of the object in deepsky.dsc, though. I'm not sure of its definition, though.

Guillermo

Hi Guillermo,

Christophe is right, of course. Since /unfortunately/ there is NO way of reading the spiral winding direction out of galaxy catalogs, I assumed a canonical winding sense (corresponding to the one of the corresponding Hubble template).

Certainly, I do not have any motivation to get 10000+ galaxies winding correctly by "handicrafting"

This would also be against my underlying philosophy in a way. The galaxy display is to strictly visualize what is available in the best galaxy catalogs, not more not less. The actual images are first of all to be viewed merely as "Hubble class icons" (NOT realistic images!) telling us about Hubble type, size, orientation in space...generic color profile.

I would not be happy if someone had the patience to turn the first 100 galaxies right, while leaving 9936 untouched because of lack of time and patience


F.

Thanks for the answer, Fridger. I understand your point and agree with it.

Anyway, what is the definition of the Axis vector in the definition of a galaxy? I still couldn't find it. (I discovered how to edit it with @, though, but I do not get feedback on the coordinates values).

Guillermo

t00fri wrote:I would not be happy if someone had the patience to turn the first 100 galaxies right, while leaving 9936 untouched because of lack of time and patience

It's clear; now on an other hand, I wonder if the 10/20 galaxies every kid have to know about (the very classical ones) should not be customize...
(We could just add a note near the readme about galaxies to let the user know what objects have the correct orientation and why the others are in this state...)

I am against doing this officially, since it is neither "fish nor meat", strategically. Everyone is welcome to flip as many galaxies as desired, using CustomTemplates. This would be a perfect project for some add-on creator...

ElChristou wrote:I wonder if the 10-20 galaxies every kid have to know about (the very classical ones) should not be customized...

While "every child knows" 10-20 galaxies, I know and have personally observed (by telescope) many, many more. So have others... Hence, were should one stop correcting? With my standards or with those of "every child"?

I think a "partial hand correction" would be a bad strategy, since it remains an uncomplete correction and since it is NOT part of ANY underlying catalogs.


F.

abramson wrote:Thanks for the answer, Fridger. I understand your point and agree with it.

Guillermo,

fine...I actually spent quite a bit of time trying to find a method for correcting the winding sense...but gave up without the slightest success.

Anyway, what is the definition of the Axis vector in the definition of a galaxy? I still couldn't find it. (I discovered how to edit it with @, though, but I do not get feedback on the coordinates values).

Guillermo

You find all rotations and axis definitions in my respective perl script in the Celestia sources. (deepsky.pl)

Fridger

t00fri wrote:You find all rotations and axis definitions in my respective perl script in the Celestia sources. (deepsky.pl)

Excellent! Many thanks. And I was looking for it on the web, while I had this right here in my celestia source distribution...

Guillermo