I am reading Richard Feynman's book Vol I. There he tells us how people usually used to find out the distance to some distant objects. I understand triangulation for objects that are near to the earth or for stars that are near to our solar system. But how did they use the same principle to find out the distance to those galaxies(which have the same diameter of our galaxy) that are far away from the earth ? Here's the excerpt- "Knowing the size of our own galaxy, we have a key to the measurement of still larger distances- the distances to others galaxies. Figure 5-7 is a photograph of a galaxy, which has much the same shape as our own. Probably it is the same size, too. (Other evidence supports the idea that galaxies are all about the same size.) If it is the same size as ours, we can tell its distance. We measure the angle it subtends in the sky; we know its diameter and we compute its distance -triangulation again" Can someone help me?