140 lines
5.6 KiB
Text
140 lines
5.6 KiB
Text
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A basic set of bright stars -- taken from the xephem program.
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Based on the 5th Revised edition of the Yale Bright Star Catalog, 1991, from
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ftp://adc.gsfc.nasa.gov/pub/adc/archives/catalogs/5/5050.
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Only those entries with a Bayer and/or Flamsteed number are retained
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here.
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Format: Constellation BayerN-Flamsteed, as available. Bayer is
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truncated as requried to enforce a maximum total length of 13
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imposed within xephem.
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Common names were then overlayed by closest position match from
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hand-edited a list supplied by Robert Tidd (inp@violet.berkeley.edu)
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and Alan Paeth (awpaeth@watcgl.waterloo.edu)
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=============================================================================
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Data file format:
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name , right assention (radians) , declination (radians) , magnitude (0.0 - 1.0)
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The following information is taken from:
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http://www.lclark.edu/~wstone/skytour/celest.html
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Please visit the above site, it contains much more complete information.
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CELESTIAL MEASUREMENTS
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RIGHT ASCENSION AND DECLINATION
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Although we know that the objects we see in the sky are of different
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sizes and at different distances from us, it is convenient to
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visualize all the objects as being attached to an imaginary sphere
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surrounding the Earth. From our vantage point, the sky certainly looks
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like a dome (the half of the celestial sphere above our local
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horizon). The celestial sphere is mapped in Right Ascension (RA) and
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Declination (Dec). Declination is the celestial equivalent of
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latitude, and is simply the Earth's latitude lines projected onto the
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celestial sphere. A star that can be directly overhead as seen from
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the Earth's Equator (0 degrees latitude) is said to be on the
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Celestial Equator, and has a declination of 0 degrees . The North
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Star, Polaris, is very nearly overhead as seen from the North Pole (90
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degrees North latitude). The point directly over the North Pole on the
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celestial sphere is called the North Celestial Pole, and has a
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declination of +90 degrees . Northern declinations are given positive
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signs, and southern declinations are given negative signs. So, the
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South Celestial Pole has a declination of -90 degrees .
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Right Ascension is the equivalent of longitude, but since the Earth
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rotates with respect to the celestial sphere we cannot simply use the
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Greenwich Meridian as 0 degrees RA. Instead, we set the zero point as
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the place on the celestial sphere where the Sun crosses the Celestial
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Equator (0 degrees Dec) at the vernal (spring) equinox. The arc of
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the celestial sphere from the North Celestial Pole through this point
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to the South Celestial Pole is designated as Zero hours RA. Right
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Ascension increases eastward, and the sky is divided up into 24
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hours. This designation is convenient because it represents the
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sidereal day, the time it takes for the Earth to make one rotation
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relative to the celestial sphere. If you pointed a telescope (with no
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motor drive) at the coordinates (RA=0h, Dec=0 degrees ), and came back
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one hour later, the telescope would then be pointing at (RA=1h, Dec=0
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degrees ). Because the Earth's revolution around the Sun also
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contributes to the apparent motion of the stars, the day we keep time
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by (the solar day) is about four minutes longer than the sidereal
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day. So, if you pointed a telescope at (RA=0h, Dec=0 degrees ) and
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came back 24 hours later, the telescope would now be pointing at
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(RA=0h 4m, Dec=0 degrees). A consequence is that the fixed stars
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appear to rise about four minutes earlier each day.
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=============================================================================
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From: steve@mred.bgm.link.com (Steve Baker)
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Subject: Re: FG: Fun in the sun ...
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Date: Tue, 5 Aug 97 15:37:27 -0500
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You probably ought to get the stars right too - there is a database
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of the 300 brightest stars in the 'Yale Bright Star Catalog' - which
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I enclose below. I'd guess that you could navigate by the stars -
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so this might not be a completely useless feature - right?
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Anyway, if all else fails - and the flight sim never gets going - we
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could at least sell this as a planetarium :-)
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The format of the star data is:
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Name Right-Ascension Declination Magnitude
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(Ascension and Declination are in radians)
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We took the magnitude value, scaled it by 0.8 and added 0.2 to make
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a 0->1 brightness value. Using the raw data created too many very
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dark stars.
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Originally, there were constellation names as sub-headings - but I
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think I deleted them to make the file easier to parse :-) That makes
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the 'name' field pretty pointless.
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if you are still talking about the geocentric coordinate system
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where the terrain is modelled with Z pointing towards the North
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pole, X out of the 0 degree meridian at the equator and Y out at the
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Indian ocean at the equator - then you can position the stars using:
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star[ X ] = fsin ( ra ) * fcos( decl ) ;
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star[ Y ] = fcos ( ra ) * fcos( decl ) ;
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star[ Z ] = fsin ( decl ) ;
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(which you can precompute at startup)
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...and then rotate them about the Z axis using GMT*two_pi/24.0
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#
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Put them all in a display list - use GL_POINTS as the primitive...
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glNewList ( ...whatever... )
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glBegin ( GL_POINTS ) ;
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for ( int i = 0 ; i < num_stars ; i++ ) {
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glColor3f ( star_brightness[i], star_brightness[i], star_brightness[i] ) ;
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glVertex3f ( star_x[i], star_y[i], star_z[i] ) ;
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}
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glEnd () ;
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glEndList () ;
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You need to draw them out by the far clip plane so they don't occult
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anything. Then you need to translate them using the same x/y/z as
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the eyepoint so that you can never fly any closer to them.
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