 Welcome to our segment on distant stars. By distant stars, I mean those stars that are so far away that parallax doesn't work anymore. Stars like this one, V838 monocerotis. In order to know how far away V838 monocerotis is, we'll need a new way to determine distance. To do that, we're going to build out a diagram that maps the star's color to its luminosity. Then we're going to study the nature of light that comes from the stars. And with that knowledge, we'll be able to use that diagram to determine the intrinsic luminosity of stars like this one. And with that, we'll know how far away they are. So let's begin with our study of light.