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Mindblown: a blog about philosophy.

  • Colors of Stars

    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, white, and blue. As we have seen, stars are not all the same color because…

  • The Brightness of Stars

    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 the Sun puts out a tremendous amount of energy every second. (And there are…

  • Thinking Ahead

    Everything we know about stars—how they are born, what they are made of, how far away they are, how long they live, and how they will die—we learn by decoding the messages contained in the light and radiation that reaches Earth. What questions should we ask, and how do we find the answers? We can…

  • The Solar Interior: Observations

    Learning Objectives By the end of this section, you will be able to: Recall that when we observe the Sun’s photosphere (the surface layer we see from the outside), we are not seeing very deeply into our star, certainly not into the regions where energy is generated. That’s why the title of this section—observations of the solar…

  • The Solar Interior: Theory

    Learning Objectives By the end of this section, you will be able to: Fusion of protons can occur in the center of the Sun only if the temperature exceeds 12 million K. How do we know that the Sun is actually this hot? To determine what the interior of the Sun might be like, it is necessary…

  • Mass, Energy, and the Theory of Relativity

    Learning Objectives By the end of this section, you will be able to: As we have seen, energy cannot be created or destroyed, but only converted from one form to another. One of the remarkable conclusions derived by Albert Einstein (see Albert Einstein) when he developed his theory of relativity is that matter can be considered a form of energy too and…

  • Sources of Sunshine: Thermal and Gravitational Energy

    Learning Objectives By the end of this section, you will be able to: Energy is a challenging concept to grasp because it exists in so many different forms that it defies any single simple explanation. In many ways, comprehending energy is like comprehending wealth: There are very different forms of wealth and they follow different…

  • Thinking Ahead

    The Sun puts out an incomprehensible amount of energy—so much that its ultraviolet radiation can cause sunburns from 93 million miles away. It is also very old. As you learned earlier, evidence shows that the Sun formed about 4.5 billion years ago and has been shining ever since. How can the Sun produce so much…

  • Space Weather

    Learning Objectives By the end of this section, you will be able to: In the previous sections, we have seen that some of the particles coming off the Sun—either steadily as in the solar wind or in great bursts like CMEs—will reach Earth and its magnetosphere (the zone of magnetic influence that surrounds our planet). As if scientists…

  • Solar Activity above the Photosphere

    Learning Objectives By the end of this section, you will be able to: Sunspots are not the only features that vary during a solar cycle. There are dramatic changes in the chromosphere and corona as well. To see what happens in the chromosphere, we must observe the emission lines from elements such as hydrogen and calcium,…

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