The Shader in Unity3D, what is the meaning of multiplying rgb by alpha?

Browse article on shaders (himself a complete novice in this matter), where as an example the following line:
half3 starAlbedo = smallStars.rgb * smallStars.a 
 + mediumStars.rgb * mediumStars.a 
 + bigStars.rgb * bigStars.a;

Tried to remove the multiplication by alpha, got the image in a strange, colorful divorces. Can somebody in simple language to explain the physical meaning of this work? or share a link which covers this issue?

PS
smallStars, mediumStars, bigStars - half4 variables which store, as I understand it, information about the channels rgba of the pixel texture which now passes through the Shader (there are 4 textures, one of which is not important for the question)
September 18th 19 at 23:54
1 answer
September 18th 19 at 23:56
Solution
Alpha by itself makes no sense, it's just another channel to transmit information. As the author of the Shader wanted the will. In the General case, the multiplication of the rgb channel by number affects the intensity of the color. The white color is multiplied by 0.5 will become grey, to zero - in black. Judging by the name of the variable in the formula is the brightness of the sky, and alpha are stored weight stars of different types, i.e., the degree of their influence on the overall brightness.

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