Could you please help answer this question.
1. (2 pts) When using the standard ruler assumption, why is it important that all of the galaxies are of the same or very similar type?
2. (3 pts) There are two probable reasons why they are not the same angular size. Either they are at the same distance and have different actual sizes, or they are the same actual size but are at different distances. Can you determine which of those two reasons is the right one? Which one of these two reasons are we assuming is true under the standard ruler method?
3. (1 pt) Compare the distances to these two galaxies as determined by the standard ruler method: NGC 3147 is 22 Mpc from us, while NGC 3368 is 15 Mpc from us. From this method, approximately how many times farther away is NGC 3147 than NGC 3368?
4. (4 pts) How do the hydrogen lines in the spectra of the galaxies add to our confidence that they are spiral galaxies and not elliptical galaxies? Consider the characteristics of both spirals and elliptical galaxies.