Nice question. I never thought about it until now. I guess some other learners also assume html to be strictly for building webpages. I think html is just for presentations, like creating a structure for other languages. However, according to the link below, html combined with other languages can be used to create games through libraries such as quintus and even through SVG or CANVAS.
As for its application in astrophysics, cosmology and physics, I don't think html is used in problem solving.