flightgear/Docs/Scenery/Astro/Stars.info

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A basic set of bright stars -- taken from the xephem program.

Based on the 5th Revised edition of the Yale Bright Star Catalog, 1991, from
ftp://adc.gsfc.nasa.gov/pub/adc/archives/catalogs/5/5050.

Only those entries with a Bayer and/or Flamsteed number are retained
here.

Format: Constellation BayerN-Flamsteed, as available. Bayer is
  truncated as requried to enforce a maximum total length of 13
  imposed within xephem.

Common names were then overlayed by closest position match from
hand-edited a list supplied by Robert Tidd (inp@violet.berkeley.edu)
and Alan Paeth (awpaeth@watcgl.waterloo.edu)


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Data file format:

name , right assention (radians) , declination (radians) , magnitude (0.0 - 1.0)


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The following information is taken from:

    http://www.lclark.edu/~wstone/skytour/celest.html

Please visit the above site, it contains much more complete information.

CELESTIAL MEASUREMENTS 

RIGHT ASCENSION AND DECLINATION

Although we know that the objects we see in the sky are of different
sizes and at different distances from us, it is convenient to
visualize all the objects as being attached to an imaginary sphere
surrounding the Earth. From our vantage point, the sky certainly looks
like a dome (the half of the celestial sphere above our local
horizon). The celestial sphere is mapped in Right Ascension (RA) and
Declination (Dec). Declination is the celestial equivalent of
latitude, and is simply the Earth's latitude lines projected onto the
celestial sphere. A star that can be directly overhead as seen from
the Earth's Equator (0 degrees latitude) is said to be on the
Celestial Equator, and has a declination of 0 degrees . The North
Star, Polaris, is very nearly overhead as seen from the North Pole (90
degrees North latitude). The point directly over the North Pole on the
celestial sphere is called the North Celestial Pole, and has a
declination of +90 degrees . Northern declinations are given positive
signs, and southern declinations are given negative signs. So, the
South Celestial Pole has a declination of -90 degrees .

Right Ascension is the equivalent of longitude, but since the Earth
rotates with respect to the celestial sphere we cannot simply use the
Greenwich Meridian as 0 degrees RA. Instead, we set the zero point as
the place on the celestial sphere where the Sun crosses the Celestial
Equator (0 degrees Dec) at the vernal (spring) equinox.  The arc of
the celestial sphere from the North Celestial Pole through this point
to the South Celestial Pole is designated as Zero hours RA. Right
Ascension increases eastward, and the sky is divided up into 24
hours. This designation is convenient because it represents the
sidereal day, the time it takes for the Earth to make one rotation
relative to the celestial sphere. If you pointed a telescope (with no
motor drive) at the coordinates (RA=0h, Dec=0 degrees ), and came back
one hour later, the telescope would then be pointing at (RA=1h, Dec=0
degrees ). Because the Earth's revolution around the Sun also
contributes to the apparent motion of the stars, the day we keep time
by (the solar day) is about four minutes longer than the sidereal
day. So, if you pointed a telescope at (RA=0h, Dec=0 degrees ) and
came back 24 hours later, the telescope would now be pointing at
(RA=0h 4m, Dec=0 degrees). A consequence is that the fixed stars
appear to rise about four minutes earlier each day.


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From: steve@mred.bgm.link.com (Steve Baker)
Subject: Re:  FG: Fun in the sun ...
Date: Tue, 5 Aug 97 15:37:27 -0500

You probably ought to get the stars right too - there is a database
of the 300 brightest stars in the 'Yale Bright Star Catalog' - which
I enclose below.  I'd guess that you could navigate by the stars -
so this might not be a completely useless feature - right?

Anyway, if all else fails - and the flight sim never gets going - we
could at least sell this as a planetarium :-)

The format of the star data is:

Name   Right-Ascension   Declination   Magnitude
        
(Ascension and Declination are in radians)

We took the magnitude value, scaled it by 0.8 and added 0.2 to make
a 0->1 brightness value. Using the raw data created too many very
dark stars.

Originally, there were constellation names as sub-headings - but I
think I deleted them to make the file easier to parse :-) That makes
the 'name' field pretty pointless.

if you are still talking about the geocentric coordinate system
where the terrain is modelled with Z pointing towards the North
pole, X out of the 0 degree meridian at the equator and Y out at the
Indian ocean at the equator - then you can position the stars using:

    star[ X ] = fsin ( ra ) * fcos( decl ) ;
    star[ Y ] = fcos ( ra ) * fcos( decl ) ;
    star[ Z ] = fsin ( decl ) ;

(which you can precompute at startup)

...and then rotate them about the Z axis using GMT*two_pi/24.0
#
Put them all in a display list - use GL_POINTS as the primitive...

  glNewList ( ...whatever... )
  glBegin ( GL_POINTS ) ;

  for ( int i = 0 ; i < num_stars ; i++ ) {
    glColor3f ( star_brightness[i], star_brightness[i], star_brightness[i] ) ;
    glVertex3f ( star_x[i], star_y[i], star_z[i] ) ;
  }

  glEnd () ;
  glEndList () ;

You need to draw them out by the far clip plane so they don't occult
anything. Then you need to translate them using the same x/y/z as
the eyepoint so that you can never fly any closer to them.