The layer’s parameters: Blending Options>Gradient Overlay

 



Make a copy of the small blue circle, represented earlier and use the Free Transform option to make the copy smaller and to place it the way it is shown below:



Next we have to select the Ellipse Tool (U) and picture a small circle on the central part of the previous blue small circle.



The layer’s parameters: Blending Options>Gradient Overlay



Gradient’s parameters:

 



For our convenience we’ll combine in a group all the layers, composing those several circles (press the Ctrl button and mark out simultaneously the necessary layers, keeping pressed the left mouse’s button we have to take the marked layers down on Create a new group option). Make three copies of the group and select the Free Transform option to change the group’s copies’ sizes



Select again the already well-known Ellipse Tool (U) and make a circle, colored with #3777A7