Hi,
I wanted to create a custom database for SN8 Pro, containing all the galaxies and quasars in the HyperLEDA catalogue down to magnitude 18. The full HyperLEDA database contains 5,377,545 entries, which was slightly more than I needed!
This post details the construction of the custom database, which contains 919,058 galaxies and quasars to magnitude 18. The custom database requires a text source file containing a series of HEADER lines to define the data, followed by the object data. Each line of data has tab separated fields.
The full process is described in the SN 8 User Guide, Adding Objects 4 (Databases) on page 133.
The data can be found on the LEDA website(http://atlas.obs-hp.fr/hyperleda/) or in my case I used the AstroPlanner HyperLEDA database.
The first problem was that the example database files did not work and gave an error complaining of a missing EPOCH field. This was easily solved by adding the column.
The SN8 data file format consists of a line of tab separated fields for each object. The fields are as follows.
Catalogue Number - Unique number, identifying the object
Catalogue Kind – The catalogue this object came from. It is possible to have several different catalogue entries within the same custom database. In this case we only have one, the HyperLEDA catalogue.
Magnitude - The objects magnitude or blank if not known.
Kind – The object type star, galaxy etc.
Epoch – The coordinates epoch, J2000 = 2000.0
RA – Degrees (0 to 360)
Dec – Degrees (-90 to 90)
Name – The name of the object (max. 30 characters). Can be blank, in which case the catalogue number and catalogue preamble header are used.
In the case of the HyperLEDA catalogue some additional information fields have been added.
Galaxy Type – Spiral (S), Elliptical(E) etc.
Surface Brightness – In magnitudes per square arc second.
Size – Major and minor axis size in arc minutes.
Position Angle – Degrees
Radial Velocity – In km/s
An example line from the data file.
1 1 16.03 13 2000.0 359.994936 0.701711 MRC2357+004 E 23.369 0.5x0.37 0 24484.7
As well as the actual catalogue (in the zip file) in the Dropbox folder. There is also a stripped down text file (HyperLEDA Test.txt) which only contains 10 entries and shows the header and data format of the source file (might be good for testing). The custom database is built by selecting File->Build Data File.. in SN8 Pro. This will create a .ssd file that has to be moved to the correct directory (see user guide). In my case on Windows 11, this would be.
C:\Users\YourUser\AppData\Local\Simulation Curriculum\Starry Night 8 Prefs\Sky Data
Restarting SN8 should allow you to turn on the database in View->Other and then click to enable or disable. The display properties can be adjusted by selecting Options->Other Options and clicking on the custom database name.
A couple of gotcha's. Firstly, the maximum number of objects in a single custom database file appears to be 1,000,000. If you exceed that, then Starry Night 8 will crash! Have 1,000,001 entries, and on my system "Big badda boom". However, I split a couple of million HyperLEDA entries into two database files and SN8 had no problem handling two large custom databases. Secondly, the header entry "NumberOfObjects" must be correct or we are back to crashing. In one of the example files it said the number didn't matter. On my system, it really did!
Anyway, here is the Dropbox link to the HyperLEDA custom database and test file. My guess is the compiled .sds file in the zip will only work on Windows PCs but hopefully you can build the database from the source text file on Macs.
I hope you find it useful.
Have fun.
Pete