I'm new to Houdini and looking for a way to get a 50% transparent shader onto a 3D sphere. The goal is to show a ramp of color where the red is at the center of the sphere, and green on the outside. Idea shown in this image from a different package.

Any advice?

Are you looking for a volume shader, or a surface shader that looks like the picture?

Great question - I don't know. I want the sphere to move with the aircraft animation. The gradient will be procedurally generated (input from a CFD application calculating aircraft noise)

Maybe better would be to express my goal: I want to represent the noise emanating from the aircraft as a color ramp that is 3D omnidirectional, and that still allows seeing the aircraft inside the “bubble.”