[BASIC OPTIONS AND TERMINOLOGY]

       In Nightfall, the <Primary> is the star passing in 
       front of the other one first, and the <Secondary> 
       thus is the star first eclipsed.

       The <mass ratio> is mass(Secondary)/mass(Primary), 
       thus it is higher than one if the Secondary is 
       more massive.

       The <inclination> is the angle, under which the 
       plane, in which the two stars orbit each other, is 
       seen from earth. Only for inclinations near 90 deg 
       (near edge-on view) an eclipse is possible.

       The <Roche lobe> is the maximum size a star can 
       have in a binary system.  It depends on the mass 
       ratio - the more massive star has the
       larger Roche lobe. If the stars overfill their Roche 
       lobes, they form a <common envelope> or <overcontact>
       system.

       To define the sizes of the two stars, you have to
       specify the <Roche lobe filling factors>, which are
       defined in units of the maximum polar radii (i.e.
       the polar radii of the Roche lobes).

       The <temperature> is the surface temperature of the 
       star. The luminosity of a star depends on its 
       surface area (i.e. size) and the temperature.

[Limiting values]

	  To avoid numerical problems, parameters are limited 
	  to reasonable values. These are:
{
          mass ratio:              0.0001 - 10000
          inclination:             0     - 90
          Roche lobe fill factor:  0.001 - 1.3
          temperature:             350   - 350000 
                                   (blackbody)
                                   2000 - 31000  
                                   (model atmosphere, log g 3.5)
                                   2000 - 39000  
                                   (model atmosphere, log g 4.0)
                                   2000 - 49000  
                                   (model atmosphere, log g 4.5)
                                   2000 - 49000  
                                   (model atmosphere, log g 5.0)
}
	  If a value is out of range, it will be reset to the 
	  lowest/highest allowed value. For Roche lobe fill
	  factors above one, the mass ratio is restricted to
	  0.003 - 50.

[Terminal Output]

	  <Warnings> will cause Nightfall to print out 
	  warnings (like parameter out of range). Usually,
	  this refers to problems Nightfall can cope with
	  by itself. In case Nightfall refuses to do what 
	  you want, it might be of some help to use this
	  option.

	  <Verbose> will print out some verbose output on 
	  what Nightfall is currently doing.

	  <Busy> will print out some status information 
	  (just enought to keep your screen busy) in case 
	  you are doing something rather lengthy, like,
	  e.g., automatic fitting of parameters to 
	  observational data.