Monday, September 5, 2016

Reading the Star Database - And Designing a Space Game

All the cataloged stars in our galaxy are available in a csv spreadsheet:
http://www.astronexus.com/hyg

Reading the Star Database:

StarID: The database primary key from a larger "master database" of stars.
HD: The star's ID in the Henry Draper catalog, if known.
HR: The star's ID in the Harvard Revised catalog, which is the same as its number in the Yale Bright Star Catalog.
Gliese: The star's ID in the third edition of the Gliese Catalog of Nearby Stars.
BayerFlamsteed: The Bayer / Flamsteed
designation, from the Fifth Edition of the Yale Bright Star Catalog. This is a combination of the two designations. The Flamsteed number, if present, is given first; then a three-letter abbreviation for the  Bayer Greek letter; the Bayer superscript number, if present; and finally, the three-letter constellation abbreviation. Thus Alpha Andromedae has the field value "21Alp And", and Kappa1 Sculptoris (no Flamsteed number) has "Kap1Scl".
ProperName: A common name for the star, such as "Barnard's Star" or "Sirius". I have taken these names primarily from the Hipparcos project's web site, which lists representative names for the 150 brightest stars and many of the 150 closest stars. I have added a few names to this list. Most of the additions are designations from catalogs mostly now forgotten (e.g., Lalande, Groombridge, and Gould ["G."]) except for certain nearby stars which are still best known by these designations.



RA, Dec:  The star's right ascension and declination, for epoch 2000.0. Stars present only in the Gliese Catalog, which uses 1950.0 coordinates, have had these coordinates precessed to 2000.

Distance: The star's distance in parsecs, the most common unit in astrometry. To convert parsecs to light years, multiply by 3.262. A value of 10000000 indicates missing or dubious (e.g., negative) parallax data in Hipparcos.
Mag: The star's apparent visual magnitude.
AbsMag: The star's absolute visual magnitude (its apparent magnitude from a distance of 10 parsecs).
Spectrum: The star's spectral type, if known.
ColorIndex: The star's color index (blue magnitude - visual magnitude), where known.
* X,Y,Z: The Cartesian coordinates of the star, in a system based on the equatorial coordinates as seen from Earth. +X is in the direction of the vernal equinox (at epoch 2000), +Z towards the north celestial pole, and +Y in the direction of R.A. 6 hours, declination 0 degrees.
* VX, 21  VY,22  VZ: The Cartesian velocity components of the star, in the same coordinate system described immediately above. They are determined from the proper motion and the radial velocity (when known). The velocity unit is parsecs per year; these are small values (around 10-5 to 10-6), but they enormously simplify calculations using parsecs as base units for celestial mapping.
(rarad. decrad pmrarad pmdecrad, bayer, flam,  con, comp,  comp primary,  base,  lum,  var,  varmin var max)

For a full list of the updated column names, see the official database documentation on Github.
Fields labeled with "*" exist only in version 2.0 or higher.

I once used this data as I was designing a game and tried to generate the whole galaxy on my computer with Cartesian coordinates. Which worked out fine although the computer got pretty warm.
The stars were still just little boring dots with basic textures and effects. Didn't make it as far as adding custom texture to a billion stars; but the Star Database includes some convenient data although not exactly the volume/size of every star - it knows the apparent visual magnitude ;)

Visual appearance.
For an observer on the Earth, the angular diameter of the Moon and the Sun are quite similar ( ~ 0.5o = 30 arcmin). In reality, the Sun's physical diameter is 400 times bigger than the Moon, while the Moon is ~ 400 times closer to the Earth.
http://www.astronoo.com/en/children/sun-apparent-size.html
It's easier to design a space game where the visual appearance of the planets and stars change rather than generating the distance.