Atmosphere Shader in Unity

Shader "Custom/Atmosphere" {
Properties{
_Color("Color", Color) = (1,1,1,1)
_Size("Atmosphere Size Multiplier", Range(0,16)) = 4
_Rim("Fade Power", Range(0,8)) = 4
_Light("Lighting Power", Range(0,10)) = 1.4
_Ambient("Ambient Power", Range(0,6)) = 0.8

}
SubShader{
Tags{ "RenderType" = "Transparent" }
LOD 200

Cull Front

CGPROGRAM
// Physically based Standard lighting model, and enable shadows on all light types
#pragma surface surf NegativeLambert fullforwardshadows alpha:fade
#pragma vertex vert

// Use shader model 3.0 target, to get nicer looking lighting
#pragma target 3.0


struct Input {
float3 viewDir;
};

half _Size;
half _Rim;
half _Light;
half _Ambient;
fixed4 _Color;

void vert(inout appdata_full v) {
v.vertex.xyz += v.vertex.xyz * _Size / 10;
v.normal *= -1;
}

half4 LightingNegativeLambert(SurfaceOutput s, half3 lightDir, half3 viewDir, half atten) {
s.Normal = normalize(s.Normal);

half diff = max(0, dot(-s.Normal, lightDir)) * _Light + _Ambient;

half4 c;
c.rgb = (s.Albedo * _LightColor0 * diff) * atten;
c.a = s.Alpha;
return c;
}

void surf(Input IN, inout SurfaceOutput o) {
half rim = saturate(dot(normalize(IN.viewDir), o.Normal));

// Albedo comes from a texture tinted by color
fixed4 c = _Color;
o.Albedo = c.rgb;
o.Alpha = lerp(0, 1, pow(rim, _Rim));
}
ENDCG
}
FallBack "Diffuse"
}