     // night
     if (sun_z < nighttime) {
         color = nightblue_color;
-        // color = vec3(phi_diff, 0,0 );
-
     // night to sunrise OR sunset to night
     } else if (sun_z > nighttime && sun_z < sun_start) {
         float size = sun_start - nighttime;

    if (phi_diff > 0.5) {
        phi_diff = 1.0 - phi_diff;
    }

    phi_diff *= 2.0;

    float sun_start;

    if (sun_x > 0) {
        sun_start = sunrise_start;
    } else {

    float sun_z = normalize(u_sun_pos).z;
    float sun_x = normalize(u_sun_pos).x;
    float sun_y = normalize(u_sun_pos).y;

    float sun_phi = acos( (sun_x) / sqrt(sun_x * sun_x + sun_y * sun_y) );
    if (sun_y < 0) {
        sun_phi = 2*PI - sun_phi;
    }
