Chapter 15 Questions

# Chapter 15 Questions - Questions for Chapter 15 From the...

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Questions for Chapter 15 From the book 1. Briefly explain how we can learn about the lives of stars, even though their lives are far longer than human lives. By taking a snapshot of space, hundreds of astronomers study the picture and obtain information about the lives of stars. 2. In what ways are all stars similar? In what ways do they differ? All stars form in great clouds of gas and dust. Each one begins its life with roughly the same chemical composition as the Sun. At birth, ¾ is hydrogen and ¼ is helium. But some stars are different in properties such as size, age, brightness, and temperature. 3. How is a star's apparent brightness related to its luminosity? Explain by describing the inverse square law for light. Apparent brightness of any star in our sky is the amount of power reaching us per unit area. Luminosity is the total amount of power that a star emits into space. Apparent brightness depends on the distance from a star. Inverse square law for light is apparent brightness = luminosity/(4pi x (distance)^2). The amount of light received per unit area decreases with increasing distance by the square of the distance. 4. Briefly explain how we use stellar parallax to determine a star's distance. Once we know a star's distance, how can we determine its luminosity? Stellar parallax is the small annual shifts in a star’s apparent position caused by Earth’s motion around the Sun. By measuring the star’s parallax angle which is equal to half the star’s back and forth shift, we can determine a star’s distance. Further stars have a smaller parallax angle. We can calculate the luminosity with the invers square law for light. 5. Other than parallax, is there a way to measure the distance to stars? Explain carefully The magnitude system originally classified stars according to how bright they look to human eyes. The brightest stars received the designation “first magnitude”, the next brightest “second magnitude”, and so on. The faintest stars were magnitude six. These are called apparent magnitudes because the compare how bright different stars appear in the sky. 6. What do we mean by a star's apparent and absolute magnitudes? How are they related to apparent brightness and luminosity? Apparent and absolute magnitudes are directly related. A larger apparent magnitude means a dimmer apparent brightness. A star’s absolute magnitude is the apparent magnitude it would have if it were at a distance of 10 parsecs from earth. Apparent brightness depends on luminosity. 7.

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Chapter 15 Questions - Questions for Chapter 15 From the...

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