FORM C 1. Slide 6 shows galaxies that are billions of parsecs away. Consider a quasar several billion parsecs away. The spiral arms of the galaxy M51 appear blue, but its central bulge is red.
Astronomers have difficulty studying the structure of the Milky Way Galaxy.
RR Lyr variables stars cannot be used to measure the Hubble Constant. An elliptical galaxy may be formed. All the interstellar gas is lost from both galaxies. A spiral galaxy is often formed. Many of the stars within the galaxies collide and go supernova.