Which of the following statements is not true of spiral arms:
they tend to trail the rotation of the galaxy
they are sites of star formation
they are amplified by resonances between the epicyclic frequencies of stars and the angular frequency of the spiral pattern
they arise simply from differential rotation
2 answers
OK, I'll give you this one, "they tend to trail the rotation of the galaxy." Oops, may be wrong.
maybe? very scientific answer...