Spiral arms appear bright because
A. they contain more hot young stars than other parts of the disk.
B. they contain far more stars than other parts of the galactic disk.
C. they contain more molecular clouds than other parts of the disk.
D. they are the only places where we find stars within the disk of the galaxy.
Answer:A
Spiral arms appear bright because
A. they contain more hot young stars than other parts of the disk. B. they contain far more stars than other parts of the galactic disk. C. they contain more molecular clouds than other parts of the disk. D. they are the only places where we find stars within the disk of the galaxy.