This example generates an animated spiral galaxy of 420 circles in SVG using D3 v7. Each circle is positioned at a radius proportional to the square root of its index and an angle based on the golden angle, with colors assigned via `d3.interpolateRainbow`. The circles transition from radius zero to their final size with staggered delays, followed by an infinite sinusoidal pulse animation using `transition.attr`. The visualization is centered in a fixed container with a light green background, rendering purely through D3’s data join and transition APIs in an ES module.