Establishing age of universe:
We now know that our galaxy is only one of some hundred thousand million that can SEEN using modern telescopes, each galaxy itself containing some hundred thousand million stars. Fig. 3.1 shows a picture of one spiral galaxy that is similar to what we think ours must look like to someone living in another galaxy. We live in a galaxy that is about one hundred thousand rotating; the stars in its undred million years. Our sun is just an ordinary, average, yellow star, near the inner edge of one of the spiral arms.