Note: A photon does have non-zero relativistic mass given by [math]m=h\nu/c^2[/math], which results directly from the Planck relation and the relativistic mass–energy equivalence formula.[/quote']Not sure I would quite say that. Really you mean it has momentum.

No. Really I meant to say it has energy. Momentum is a separate issue.

 

Let me be real clear: A photon has zero invariant¹ mass, non-zero momentum, and non-zero energy.

 

¹I much prefer the terms "invariant mass" and "intrinsic mass" to "rest mass". A photon always moves at c, so the term "rest mass" is a bit of an oxymoron to me. The qualifiers invariant and intrinsic when applied to mass don't ring any jumbo shrimp / death benefit alarm bells in my head.

And once you have established that you are interested in invariant mass rather than relativistic mass, you have to decide whether or not you want pole mass or running mass...