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

question 169

Multiple Choice

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.

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