Astronomy › Section S · The Milky Way › Topic S.2
Spiral structure
Photographs of other galaxies show graceful spiral arms, but we cannot photograph our own from outside. Radio and infrared maps show that the Milky Way has arms too, and explaining why they last turns out to be a real puzzle.
In this topic
- Arms we cannot see directly
- Turning velocities into a map
- The arms of the Milky Way
- Differential rotation
- Worked example: the winding problem
- Density waves: arms as traffic jams
- Why arms glow with young stars
- Worked example: how far does a blue star wander?
- Other ideas and arms through time
- Common mistakes to avoid
- Key takeaways
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