Help with stars and galaxies homework
Maksettu toimituksen yhteydessä
1. Describe two ways of determining the diameter of a star.
2. Describe the connection between cepheid variable stars and the period-luminosity relation
3. Explain how you would use the spectrum of a star to estimate its distance.
4. Which method would you use to obtain the distance to each of the following?
a. An asteroid crossing Earth's orbit
b. A star astronomers believe to be no more than 50 light-years from the Sun
c. A tight group of stars in the Milky Way Galaxy that includes a significant number of variable stars
d. A star that is not variable but for which you can obtain a clearly defined spectrum
Why do nebulae near hot stars look red? Why do dust clouds near stars usually look blue?
5. Describe how the 21-cm line of hydrogen is formed. Why is this line such an important tool for understanding the interstellar medium?
6. Give several reasons the Orion molecular cloud is such a useful "laboratory" for studying the stages of star formation.
7. Explain why we have learned a lot about star formation since the invention of detectors sensitive to infrared radiation.
8. How is a nova different from a type Ia supernova? How does it differ from a type II supernova?
9. Describe the evolution of a pulsar over time, in particular how the rotation and pulse signal changes over time.
10. A star is often described a "moving" on an H-R diagram; why is this description used and what is actually happening with the star?
11. How does the equivalence principle lead us to suspect that spacetime might be curved?
12. If general relativity offers the best description of what happens in the presence of gravity, why do physicists still make use of Newton's equations in describing gravitational forces on Earth (when building a bridge, for example)?
13. If a black hole itself emits no radiation, what evidence do astronomers and physicists have that the theory of black holes is correct?
14. What is a gravitational wave and why was it so hard to detect?
15. Describe the evidence indicating that a black hole may be at the center of our galaxy.
16. What will be the long-term future of the Milky Way?
17. What are the two best ways to measure the distance to a nearby spiral galaxy, and how would it be measured?
18. Describe some differences between quasars and normal galaxies.
19. Describe the observations that convinced astronomers that M87 is an active galaxy.
20. Describe the evolution of an elliptical galaxy. How does the evolution of a spiral galaxy differ from that of an elliptical?
21. What is the evidence that a large fraction of the matter in the universe is invisible?
22. Which formed first: hydrogen nuclei or hydrogen atoms? Explain the sequence of events that led to each.
23. Astronomers have found that there is more helium in the universe than stars could have made in the 13.8 billion years that the universe has been in existence. How does the Big Bang scenario solve this problem?
24. Describe the evidence that the expansion of the universe is accelerating.
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