What is beauty?

How do we decide something looks beautiful? Like a face, a mountain range, a sunset, an animal, a great ass, a painting, or a body of water? A sunset is just a bunch of colors blending together, yet it looks beautiful. I might see a pair of legs and think it is just gorgeous. Some paintings just blow my mind. What is it about these things that appeals to us so much? Why are some faces just amazing while others do nothing for us? What’s at the heart of the matter?