I hear a lot about astronomers using type IA supernovae to accurately measure large scale distances over billions of light years to do things like measure the rate of expansion of the universe. I doubt that the calculation of this distance is simply based on the inverse square law. So my question is what other factors are used in calculating that distance? One I can think of off the top of my head is from SR we know that objects traveling quickly away from us have their emitted light red shifted and luminosity reduced. We can see the red shift in these distant galaxies but do the astronomers account for the proper amount of reduction in light intensity when calculating these distances?