LEARNING OBJECTIVES By the end of this section, you will be able to: In this chapter and Analyzing Starlight, we described some of the characteristics by which we might classify stars and how those are measured. These ideas are summarized in Table…
LEARNING OBJECTIVES By the end of this section, you will be able to: It is easy to measure the diameter of the Sun. Its angular diameter—that is, its apparent size on the sky—is about 1 If we know the angle…
LEARNING OBJECTIVES By the end of this section, you will be able to: The mass of a star—how much material it contains—is one of its most important characteristics. If we know a star’s mass, as we shall see, we can estimate how…
LEARNING OBJECTIVES By the end of this section, you will be able to: Before we can make our own survey, we need to agree on a unit of distance appropriate to the objects we are studying. The stars are all…
Figure 18.1 Variety of Stars. Stars come in a variety of sizes, masses, temperatures, and luminosities. This image shows part of a cluster of stars in the Small Magellanic Cloud (catalog number NGC 290). Located about 200,000 light-years away, NGC 290 is about 65 light-years…
The Brightness of Stars The total energy emitted per second by a star is called its luminosity. How bright a star looks from the perspective of Earth is its apparent brightness. The apparent brightness of a star depends on both…
LEARNING OBJECTIVES By the end of this section, you will be able to: Analyzing the spectrum of a star can teach us all kinds of things in addition to its temperature. We can measure its detailed chemical composition as well…
LEARNING OBJECTIVES By the end of this section, you will be able to: Measuring colors is only one way of analyzing starlight. Another way is to use a spectrograph to spread out the light into a spectrum (see the Radiation and…
LEARNING OBJECTIVES By the end of this section, you will be able to: Look at the beautiful picture of the stars in the Sagittarius Star Cloud shown in Figure 17.3. The stars show a multitude of colors, including red, orange, yellow,…
LEARNING OBJECTIVES By the end of this section, you will be able to: Luminosity Perhaps the most important characteristic of a star is its luminosity—the total amount of energy at all wavelengths that it emits per second. Earlier, we saw that…