1 Mega-stars STC file for M31

[Cham]

I even discovered that one of the axes used by Celestia is actually reversed, compared to the usual conventions in science and maths.

Would that be the same axes Fridger and and Ajtribick had a standoff over in the Binary Radial Velocities thread, by any chance?

I can't tell. I don't know.

I only know that when I defined my Mathematica code to match the galaxies orientation, using the DSC parameters found in Fridger's galaxies.dsc file, I had to reverse one axis. I had troubles to find this reversal issue, since it's contrary to the usual vectorial product rule (right hand rule).

I strongly suspect that the inversion is located in Celestia's way of defining orientation.

[danielj]

I opened using Winzip.I don?t have TextFile.

[John Van Vliet]

--- edit ---

[Fenerit]

danielj
i know that in the past i have mentioned a VERY good text editor for windows

SciTE
http://www.scintilla.org/SciTE.html
better than "notebook+" in my opinion

or Scintilla
http://www.scintilla.org/

Hi John, if "notebook+" = "notepad++", its core is Scintilla.

[PlutonianEmpire]

Hmmmmm.....

Would it be unreasonable or outrageous or something to expect a potential possibility of a distribution for.... I dunno.... Maybe say....








The Milky Way?

[omega13a]

Yes, Celestia need a tool to build binary STC files.
Currently, it recognize only one binary file, and it must be placed in its data folder.

Very sad.

Theorically, it could be possible to put convert the data from the stc file into the same format as the data on the text file used to make that binary file and append the data at the end of the file. You could then recompile celestia and replace the old binary file with the new one. The only problem is that each star would need to be assigned a HIP number... Even if Celestia could look in the extras folder for binary stc files, we would still have a problem with the HIP numbers. It could cause some collisions between add-ons.

[PlutonianEmpire]

Yes, Celestia need a tool to build binary STC files.
Currently, it recognize only one binary file, and it must be placed in its data folder.

Very sad.

Theorically, it could be possible to put convert the data from the stc file into the same format as the data on the text file used to make that binary file and append the data at the end of the file. You could then recompile celestia and replace the old binary file with the new one. The only problem is that each star would need to be assigned a HIP number... Even if Celestia could look in the extras folder for binary stc files, we would still have a problem with the HIP numbers. It could cause some collisions between add-ons.

Perhaps then, the .dat compiler/compilation process could be rewritten to allow inclusion of stars without hip numbers (eg, saying "star" instead of a hip number, as already done in .stc files)?

[Averus]

First thought upon seeing this add-on - very nice, gotta try it.

Second thought after reading through the thread, trying to load it and quitting after a 3 minute wait - this will simply not stand!

And thus I have converted all 1 million star coordinates, types and luminosities into a .dat file (M31.dat, 11.4 MB packed, 19 MB unpacked) for everyone to enjoy with quick loading times:

https://docs.google.com/open?id=0BwLaKHFs5JgxV2p5eEdHYnhiOUE

Unfortunately, it's not an exact replica - the positions of the stars differ slightly from the original, probably due to the fact that the coords in the .dat files are stored as 4-byte floats in light-years and the distances from the Sun are so huge that this level of precision is not enough. However the errors seem to be on the smaller side (0 - 0.15 ly from the original position), and the loading times are much faster so I think it's a fair trade-off.

I have also created another .dat file (MW_M31.dat, 43.2 MB packed, 58.6 MB unpacked) - it's a result of the merger between 2.1C Star Database and this one, for anyone who wants to keep the Milky Way stars and enjoy the Andromeda Galaxy at the same time!

https://docs.google.com/open?id=0BwLaKHFs5JgxaEVpMnVQM2hSa3M

The new stars are numbered HIP 10000001 to 11000000 - this maps to some Tycho identifiers, but if you put in "HIP 11000000" in the search box it will find it just fine.


HOW TO USE IT - you probably know it already, but for anyone in need:

0. Unpack the downloaded file.

1. For Andromeda Galaxy alone - backup your original Celestia/data/stars.dat file, rename M31.dat to stars.dat and put it in the Celestia/data folder.

OR

1'. For Milky Way and Andromeda Galaxy goodness - backup your original Celestia/data/stars.dat file, rename MW_M31.dat to stars.dat and put it in the Celestia/data folder.


Lastly - two questions to the author:
What does the "CM1" spectral type represent? I couldn't find any info on it, and since Celestia seemed to map it to M1 I did so as well during the conversion.
The other matter is a technicality - there seem to be almost no stars in the core region of the M 31, was it like this in the original distribution too or did the conversion mess it up?

[PlutonianEmpire]

1. Unfortunately, it appears as though the lack of core stars is indeed part of the original distribution.

2. The 2 million stars database is a bit outdated. It was last updated for 1.4.0 in 2009. Even if it's only been 3 years, I'm sure the current data available for a lot of the stars is a lot better than when these .dat's were last compiled.

[Cham]

Guys, let me remind you that you are off-topic. You should start a new topic to discuss these matters...

[selden]

I've moved the off-topic posts about star catalog accuracy to
viewtopic.php?f=23&t=17081
with the title "Accurate star data" [...]