code: function (nightImageSource) {
              Layer.call(this, "Atmosphere");
  
              // The atmosphere layer is not pickable.
              this.pickEnabled = false;
  
              //Documented in defineProperties below.
              this._nightImageSource = nightImageSource ||
                  WorldWind.configuration.baseUrl + 'images/dnb_land_ocean_ice_2012.png';
  
              //Internal use only.
              //The light direction in cartesian space, computed from the layer time or defaults to the eyePoint.
              this._activeLightDirection = new Vec3(0, 0, 0);
  
              this._fullSphereSector = Sector.FULL_SPHERE;
  
              //Internal use only. Intentionally not documented.
              this._skyData = {};
  
              //Internal use only. The number of longitudinal points in the grid for the sky geometry.
              this._skyWidth = 128;
  
              //Internal use only. The number of latitudinal points in the grid for the sky geometry.
              this._skyHeight = 128;
  
              //Internal use only. Number of indices for the sky geometry.
              this._numIndices = 0;
  
              //Internal use only. Texture coordinate matrix used for the night texture.
              this._texMatrix = Matrix3.fromIdentity();
  
              //Internal use only. The night texture.
              this._activeTexture = null;
          }
docs: Constructs a layer showing the Earth's atmosphere.
  @alias AtmosphereLayer
  @constructor
  @classdesc Provides a layer showing the Earth's atmosphere.
  @param {URL} nightImageSource optional url for the night texture.
  @augments Layer