anchor.diff:              //let stars = ursaMajorStars
               let dirs = stars |> Array.map (fun s -> V3f(Conversion.CartesianFromSpherical(s.RArad, s.DErad)))
       
  +            let intScalePerMag = float32 (Fun.Pow(100.0, 1.0/5.0)) // intensity scale per magnitude ~2.511
  +            let i0 = 0.0325f // luminance of star with mag 0.0 / ~luminance of vega
  +
               let colors = 
                   stars 
                   |> Array.map (fun s -> 
  -                    let mag = s.Hpmag
  -                    let intScalePerMag = float32 (Fun.Pow(100.0, 1.0/5.0)) // ~2.511
  -                    let i0 = 0.0325f // luminance of star with mag 0.0 / ~luminance of vega
  -                    let l = i0 / (pow intScalePerMag mag) // mag -26.7 -> 1.6e9 (per solar disc size), mag -12.7 average full moon -> 2.5e3
  +                    let l = i0 / (pow intScalePerMag s.Hpmag) // mag -26.7 -> 1.6e9 (per solar disc size), mag -12.7 average full moon -> 2.5e3
                       // luminance the star would have if sun was 1px -> scale with viewportSize and fov (currently in shader)
                       C4f(l, l, l, 1.0f)
                   )
  
positive.code:                     let polColLum = Vec.dot (polCol.ToV3d()) lumVector
                      pol * polCol.SRGBToXYZinC3f().ToC3d() / polColLum
      
                  let sunScale = nightTimeFadeout theta
                                         
                  let cubeFaces = Array.init 6 (fun i -> 
                      PixImage.CreateCubeMapSide<float32, C4f>(i, res, 4, 
                          fun v ->
                              let mutable xyz = C3f.Black
                              xyz <- xyz + skySun.GetRadiance(v).ToC3d() * sunScale
                              xyz <- xyz + skyMoon.GetRadiance(v).ToC3d() * 2.5e3 / 1.6e9 * moonRefl // TODO: actual amount of reflected light
                              xyz <- xyz + (lightPolFun v) * pol
                              let rgb = xyz.XYZinC3fToLinearSRGB().Clamped(0.0f, Single.MaxValue)
                              if rgb.ToV3f().AnyNaN then 
  
negative.code: 
                  let size = 
                      (planetScale, dirAndDistance) ||> AVal.map2 (fun ps (struct (_, _, distance)) -> 
                          let distKm = Astronomy.AU / 1000.0 * distance // convert distance from AU to km
                          let radius = atan (r / distKm)
                          radius * (pow ps 2.5) // diameter in radians * user factor
                      ) 
  