Celestia Forums

I need the AbsMag values for all the Messier's globular clusters. Someone has an idea where I can find these ? I know the approximate average value is AbsMag -9, but I need something more precise for each of the 29 Messier globular clusters.

The SEDS pages seem to have apparent magnitudes for most of them.
e.g.
http://www.seds.org/messier/m/m002.html

And, of course, you can query the Simbad database at http://simbad.u-strasbg.fr/

Selden,

about the AbsMag of the Messier Globular Clusters, I'm finding lots of unreliable values on the net. Distances also seems to contains LOTS of variations on the net, so I'm not sure I can trust any other values than the mean one of AbsMag -9 that I gave to all your globular clusters. I'm finding values between -8 and -10 for all the globular clusters. So I think it's preferable to give them all the same -9 value, since other numbers can't be trusted. In Celestia, a variation of about +/- 1 doesn't make much a difference. What do you think ?

This is ridiculous ! On those two web pages, I'm finding very different numbers for the apparent magnitude of the Messier globular clusters :

http://www.seds.org/messier/objects.html#cluster

http://en.wikipedia.org/wiki/List_of_Messier_objects

Maybe I'm stupid and there's something I'm unaware of, or I'm overlooking something. Can somebody explain to me why the AppMag are so different here ?

EDIT : Geez ! On the Wikipedia pages, I'm finding the same AppMag as on the other source, but only if I click on each Messier object. FGor example, that page :

http://en.wikipedia.org/wiki/Globular_Cluster_M10

gives an AppMag 6.6 while it is 7.5 in the list !!

Ok, I finally have the AbsMag right. Here's a link to the files :

http://nho.ohn.free.fr/celestia/Cham/Messier_all_v3.zip

Wikipedia is far from perfect. It's a continual work in progress. Can you tell at all what the numbers listed under Apparent Magnitude actually are on that List of Messier Objects? If I knew what adjustments need to be made, I can fix the list as need be.

it's allright, the AbsMag are fixed. Everything is working properly, now

I hope to convince Chris to add those Messier objects in the official distribution.

No, what I mean is, I'd like to fix the list in Wikipedia, if it's broken, which as I'm understanding, it currently is.

Johaen wrote:No, what I mean is, I'd like to fix the list in Wikipedia, if it's broken, which as I'm understanding, it currently is.

Yes, that wikipage seems to have some incoherences.

The values on the Simbad server are taken directly from professional astronomers' research.
Since that server's database is maintained by professionals, it's as accurate and reliable as any you'll find published anywhere. It also includes references to the original published documents.

Unfortunately, Wikipedia is open for editing by anyone. You have to be careful about pages being modified by well meaning but misinformed individuals, as well as intentional defacement.

Cham wrote:I hope to convince Chris to add those Messier objects in the official distribution.

Why that?

All data required are in (the latest version of) Steinecke's revised NGC/IC catalog that is also the source of my 10000+ galaxies in the Celestia distribution. It is presently the most concise /and uniform/ source of parameters for deepsky objects. My respective PERL script extracts all required data from the revised NGC/IC catalog precisely in the .dsc form required by Celestia.

As soon as find a bit of time, I'll proceed to include the missing objects from that catalog in the distribution along with the appropriate sprite rendering code. All coordinates and size parameters in the Steinecke catalog are refitted against the DSS photographic survey.
There is no reason whatsoever to use other less accurate sources for these objects. As Selden pointed out already, only professional data should be used. Steinecke is one of the lead scientists of the ongoing NGC/IC project. The references you find in my deepsky.dsc file of the distribution.


Bye Fridger

PS: I have not responded so far, since your post was in P&A...

Fridger,

I wasn't aware of your progress on the Messiers objects, and it was OBVIOUS many M objects are still missing in Celestia, which is a very bad thing for an astronomy program. I hope you'll add the data soon enough to be included in the next release of the official package. IMHO, it's a shame that the Messiers objects (not just your galaxies) aren't included in the base package. This had to be corrected and I was working on that, without knowing you were already planing to do it yourself. Having said that, my database is good enough and ready to be part of the package.

Cham wrote:Fridger,

I wasn't aware of your progress on the Messiers objects, and it was OBVIOUS many M objects are still missing in Celestia, which is a very bad thing for an astronomy program. I hope you'll add the data soon enough to be included in the next release of the official package. IMHO, it's a shame that the Messiers objects (not just your galaxies) aren't included in the base package. This had to be corrected and I was working on that, without knowing you were already planing to do it yourself. Having said that, my database is good enough and ready to be part of the package.

Cham,

producing the parameter listing of all NGC/IC or their (small) Messier-subset is just a single command with my PERL-script (with just a different object number from that of galaxies) that exists since a long time.

But the far harder part concerns the respective rendering code. That's why this project is still in progress. Galactic clusters are very easy to render with sprites. However there are also many gaseous nebulae without obvious symmetries, like M42 (Orion) M57 (Lyra), M17 (Omega), Trifid etc and many other NGC/IC objects. I do have a very promising rendering strategy at least for a special class of nebulae, socalled bipolar planetaries that have been shown to be axially symmetric to very good approximation.

Certainly this project will not be finished for the next Celestia version, which is supposed to be due quite soon.

However, in the forthcoming version, there will be some nice progress concerning galaxies, about which I shall report quite soon in the Developer Talk board. This also includes a set of completely new PNG templates (all designed in collaboration with ElChristou!), along with possible custom templates, like one for the MilkyWay, which I am sure you will like, since it will implement all well-established features.

Another issue to take into account as to calculating absolute magnitudes, is the used filter system standard (Johnsson, Tycho...), and the used angular size fraction for the apparent magnitude measurements! To reduce given apparent mag data to absolute ones, some (partly tricky) corrections have therefore to be applied.

Times are long over where one simply can combine some given ("anonymous") values from different badly documented resources like e.g. Wikipedia...Furthermore, in Celestia, we have agreed that all modifications (including removal of typos) from published values are to be clearly documented (e.g. in human readable PERL scripts) .

Bye Fridger

PS: Sorry if I will not go on replying here, but as you sure know, the P&A board is not for me anymore

t00fri wrote:PS: Sorry if I will not go on replying here, but as you sure know, the P&A board is not for me anymore

Aaah c'mon Fridger ! This topic is already a good P&A topic, AFAIK. Anyway, I agree with you and the project you have in mind.

As a side note, is it possible to remove the annoying space in the Messier object names (M5 instead of M 5) ? Selden and myself believe it's better without the space. However, for the NGC objects, I don't care much about a space or not, but in the case of the Messier objects, I believe there shouldn't be any space in the names. What do you think ?

Cham wrote:...As a side note, is it possible to remove the annoying space in the Messier object names (M5 instead of M 5) ? Selden and myself believe it's better without the space. However, for the NGC objects, I don't care much about a space or not, but in the case of the Messier objects, I believe there shouldn't be any space in the names. What do you think ?...

I'm not an expert to argue about this, but as a common user I agree the space is a bit annoying...