21^st Century Astronomy, Second Edition

Chapter 15: Star Formation and the Interstellar Medium

Study Plan

When you look at the night sky it is stars that you notice, yet stars fill only the tiniest fraction of the volume of space. On this leg of our journey we turn our attention to the tenuous medium between the stars, and we discover that

• There are various phases of the interstellar medium, ranging from cold, relatively dense molecular clouds to hot, tenuous, intercloud gas.
• Different phases of the interstellar medium emit various types of radiation and can be observed at different wavelengths, ranging from radio waves to X-rays.
• Dust in the interstellar medium blocks visible light but glows with infrared radiation.
• Gas in the interstellar medium is heated and ionized by energy from stars and stellar explosions.
• Stars form in clusters from dense cores buried within giant molecular clouds.
• Forming stars are seen by their infrared emission and by the effects they have on their surroundings.
• We can follow the progress of an evolving protostar by its track across the H-R diagram.
• Protostars collapse, radiating away their gravitational energy until fusion starts in their cores, and they settle onto the main sequence.

Organize

1. Read Chapter 15 in your textbook or ebook.
2. Take the Diagnostic Quiz to assess your understanding of the basic concepts and identify gaps in your understanding of the assigned reading.

Learn

1. Access the Animations given for this chapter. These brief lessons enhance your understanding of core concepts.
   Star Formation
   Section: 15.3, 15.4
2. Use the FlashCards to test your memory for new terms.
3. If your instructor has assigned SmartWork online homework, login from the right navigation pane for additional practice and review.

Connect

1. Periodic Connections boxes and the Seeing the Forest through the Trees section at the chapter's end draw your attention to recurring themes and help prepare you for concepts explored more fully in subsequent chapters.
2. Visit Astronomy in the News for breaking news of new discoveries and the opportunity to apply what you've learned in this chapter to real-world (and real Universe) events.

Instructors now have an easy way to collect students’ online quizzes with the Norton Gradebook without flooding their inboxes with e-mails.

Students can track their online quiz scores by setting up their own Student Gradebook.