I'll need some help with the globular clusters

[Spaceman]

Hello

Yesterday I was flying inside a couple of globular clusters, like 47 Tucanae, and I was thinking about making my own fictional clusters. I have a fictional system from the ArcBuilders Universe and I tried today to make a fictional globular cluster to fill the empty space around it with some stars. I used the 47 Tucanae as a base, changed some numbers, and made a .dsc file at the extras folder with this:

Code: Select all

Globular "Magni Cluster"
{
   RA   79.683917
   Dec   33.412025
   Distance   11800
   Radius   100
   CoreRadius   0.4
   KingConcentration   2.03
   AbsMag   -5.00
   Axis   [ -0.7429 -0.2364 -0.6263 ]
   Angle   175.9
}

The problem is that Celestia doesn't load it, doesn't even recognize it. I hit ENTER, try to type the name of the cluster, and there isn't in the list at all. What I did wrong? I don't get it.

By the way, I have some questions about globular clusters. How big can they get? What exactly is the CoreRadius? What will happen if it has the same value with the Radius? KingConcentration is about spreading the cluster, making the core more or less dense? What's its maximum value? What exactly are Axis and Angle? Can I make a cluster big enough and spread its stars with such a uniformity, to fill some caps in Space?

[LukeCEL]

Hi Spaceman!

I tried your DSC code and it worked for me.

The only "wrong" with your DSC file is that the RA is too high - for DSC files the RA is in fractional hours, not degrees, so it goes from 0 to 24. However, the globular will still work, it'll just be placed in an unexpected position.

A while ago, I made a spreadsheet that helps generate globular clusters. It's meant for real objects, but it could still be helpful for your endeavors. viewtopic.php?f=25&t=20284

For me, globular clusters are still mostly a mystery, but I think I can answer a few questions:

KingConcentration is about spreading the cluster, making the core more or less dense? What's its maximum value?

The KingConcentration parameter is the log of the tidal radius divided by the core radius (why it says c = log10(r_t/r_c) in globulars.dsc). So my guess is that a higher KingConcentration makes it more clustered, but I don't know. I also don't know what the maximum value is.

What exactly are Axis and Angle?

The Axis and Angle values specify the orientation of the globular cluster. Currently, though, they're kinda useless because globular clusters look the same from any direction.

Best,
LukeCEL

[Spaceman]

Thanks for the help, Luke. I'll give your generator a try for sure. I fixed the RA value and I really hoped this was the problem. Still nothing. Celestia can't even find it.

There is supposed to be a globular cluster here :(

By the way, I have Celestia Origin version 1.6.0.

[Gurren Lagann]

I do see a really dim spec of light right next to your marker though... That could be the cluster.

Marker: star - Blurry dot: possible cluster

whereismycluster~2.jpg (1.15 KiB) Viewed 7169 times

[Spaceman]

No, that's a detail of the nebula next to the Magni Sun.