What, "Physically" is a Spherical Harmonic? I'm trying to use spherical harmonics to get an equation to fit a set of data I have. I'm fine with that, I've found a derivation of what the general form is and I crunch that into MATLAB. My problem is derivations online really don't help me understand what this thing is, not really. I'm an engineer and my grasp of abstract math concepts really isn't that good. I have a bunch of points now that my model churned out that are complex. I need to be able to compare the results of my model to the actual data before I use my model for other purposes, and I have no idea if I can just use the real part or not because I physically do not understand what this equation I have represents. It's easy enough to tell me that Fourier is the idea you can approximate ANY equation with a sum of sines and cosines. That physically makes sense to me. Somehow a spherical should be Fourier in two dimensions from what I've gathered. But now we're complex and I just have no idea in what situations you use the real part, imaginary part, both parts?