How to properly implement A timeline for multiple scale transitions in JavaFX program

Question

In my program, I have already created a bullseye. The circles that are already inside the bullseye will shrink once the user presses the animate button. After, I want this program to run so that circles will appear behind the pre-existing cirlces (which are still shrinking) and this cycle of shrinking circles will continue untill the user presses the stop button.

My problems are coming from the timeline that I failed to implement. I am not entirely familiar with how to properly implement a timeline with the scale transitions that I have made.

public class Target extends Application 
{
    Circle[] cir = new Circle[7];
    Button btn = new Button("Animate me!");
    StackPane root = new StackPane();

    public static void main(String[] args) 
    {
        launch(args);
    }

    /** 
     * start method will create the target and the start button first 
     * displayed on-screen to the user 
     */
    @Override
    public void start(Stage primaryStage) 
    {

        root.setStyle("-fx-border-color:black;");      

        cir[0] = new Circle(400, 250, 200);
        cir[0].setFill(Color.RED);
        cir[0].setStyle("-fx-border-color:black;");

        cir[1] = new Circle(315, 165, 115);
        cir[1].setFill(Color.WHITE);
        cir[1].setStyle("-fx-border-color:black;");

        cir[2] = new Circle(230, 80, 30);
        cir[2].setFill(Color.RED);
        cir[2].setStyle("-fx-border-color:black;");

        root.getChildren().addAll(cir[0], cir[1], cir[2]);      
        root.getChildren().add(btn);      

        primaryStage.setScene(new Scene(root));
        primaryStage.show();

        btn.setOnAction(e ->
        {
            animation();
            btn.setText("Press to Stop");
        });
    }

    public void animation()
    {
        Timeline animation = new Timeline(
        )

        ScaleTransition[] st = new ScaleTransition[7];
        boolean recycleCircles = false;

        st[0]= new ScaleTransition(Duration.seconds(7), cir[0]);
        st[0].setToX(0.0f);
        st[0].setToY(0.0f);
        st[0].play();

        st[1] = new ScaleTransition(Duration.seconds(5.5), cir[1]);
        st[1].setToX(0.0f);
        st[1].setToY(0.0f);
        st[1].play();

        st[2] = new ScaleTransition(Duration.seconds(4), cir[2]);
        st[2].setToX(0.0f);
        st[2].setToY(0.0f);
        st[2].play();

       // int delayInc = 1;
        int delay = 1;

        //will create circles (will rotate between white and red) and then add 
        //to scaleTransitions
        //while(btn.isPressed() == false)
        {     
            for(int i = 3; i<st.length; i++)
            {     
                if(recycleCircles == true)
                {
                    i = 0;
                    recycleCircles = false;
                }
                if(i % 2 == 1)
                {
                    cir[i] = new Circle(400,250,200);
                    cir[i].setFill(Color.WHITE);
                    cir[i].setStyle("-fx-border-color:black;");
                    root.getChildren().add(cir[i]);
                    cir[i].toBack();

                    st[i] = new ScaleTransition(Duration.seconds(7), cir[i]);
                    st[i].setDelay(Duration.seconds(delay));
                    delay++;
                    st[i].setToX(0.0f);
                    st[i].setToY(0.0f);
                    st[i].play();

                }
                else if(i%2==0)
                {
                    cir[i] = new Circle(400, 250, 200);
                    cir[i].setFill(Color.RED);
                    cir[i].setStyle("-fx-border-color:black;");
                    root.getChildren().add(cir[i]);
                    cir[i].toBack();

                    st[i] = new ScaleTransition(Duration.seconds(7), cir[i]);
                    st[i].setDelay(Duration.seconds(delay));
                    delay++;
                    st[i].setToX(0.0f);
                    st[i].setToY(0.0f);
                    st[i].play();
                }
                if(i == 6)
                    recycleCircles = true;
            }
        }

        //btn.pressedProperty().addListener(listener);

        btn.setOnMousePressed(event ->
        {   
        });   

        btn.setOnMouseReleased(event -> 
        {
            for(int y = 0; y<st.length;y++)
            {       
            }
        });


    }  
}