Which one of these statements about the spiral arms of grand-design spirals is true?
A) The density of matter in the spiral arms is many times the density of the regions in between.
B) The regions between the spiral arms are cloaked in dust, which makes them look dimmer than the spiral arms.
C) The spiral density waves, which move around the galaxy, are transverse waves, moving up and down across the direction of the waves motion like light waves.
D) The spiral arms have almost the same density as the rest of the disk. They are more visible because they contain bright, newly formed stars.

Question

Quizplus · Accepted Answer

The spiral arms of grand-design spirals are more visible not because they have a significantly higher density of matter compared to the rest of the disk, but because they contain bright, newly formed stars. These stars illuminate the arms, making them stand out against the background of the galaxy.

Which One of These Statements About the Spiral Arms of Grand-Design