If I use light years to describe large reception distances,say 10 billion,am I also stateing the light travel time? The way I figure it at these distances you would have to increase the light travel time useing the hubble constant to quantify the increase in space a photon would have to travel. Kind of like swiming against a current to reach a destination.Parasecs are what I should state as a distance modulus at these lengths,but that does'nt describe light travel time. So,when useing LYs are you stateing distance & light travel time or just distance? This has been bugging me for a while now!! Please help me out with this one. Thanks.