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Mindblown: a blog about philosophy.

  • Ocean Tides and the Moon

    Learning Objectives By the end of this section, you will be able to: Anyone living near the sea is familiar with the twice-daily rising and falling of the tides. Early in history, it was clear that tides must be related to the Moon because the daily delay in high tide is the same as the daily delay…

  • Phases and Motions of the Moon

    Learning Objectives By the end of this section, you will be able to: After the Sun, the Moon is the brightest and most obvious object in the sky. Unlike the Sun, it does not shine under its own power, but merely glows with reflected sunlight. If you were to follow its progress in the sky for a…

  • The Calendar

    Learning Objectives By the end of this section, you will be able to: “What’s today’s date?” is one of the most common questions you can ask (usually when signing a document or worrying about whether you should have started studying for your next astronomy exam). Long before the era of digital watches, smartphones, and fitness…

  • Keeping Time

    Learning Objectives By the end of this section, you will be able to: The measurement of time is based on the rotation of Earth. Throughout most of human history, time has been reckoned by positions of the Sun and stars in the sky. Only recently have mechanical and electronic clocks taken over this function in…

  • The Seasons

    Learning Objectives By the end of this section, you will be able to: One of the fundamental facts of life at Earth’s midlatitudes, where most of this book’s readers live, is that there are significant variations in the heat we receive from the Sun during the course of the year. We thus divide the year…

  • Earth and Sky

    Learning Objectives By the end of this section, you will be able to: In order to create an accurate map, a mapmaker needs a way to uniquely and simply identify the location of all the major features on the map, such as cities or natural landmarks. Similarly, astronomical mapmakers need a way to uniquely and…

  • Thinking Ahead

    If Earth’s orbit is nearly a perfect circle (as we saw in earlier chapters), why is it hotter in summer and colder in winter in many places around the globe? And why are the seasons in Australia or Peru the opposite of those in the United States or Europe? The story is told that Galileo, as…

  • Collaborative Group Activities

  • For Further Exploration

    For Further Exploration Articles Brahe and Kepler Christianson, G. “The Celestial Palace of Tycho Brahe.” Scientific American (February 1961): 118. Gingerich, O. “Johannes Kepler and the Rudolphine Tables.” Sky & Telescope (December 1971): 328. Brief article on Kepler’s work. Wilson, C. “How Did Kepler Discover His First Two Laws?” Scientific American (March 1972): 92. Newton Christianson, G. “Newton’s Principia: A Retrospective.” Sky &…

  • Gravity with More Than Two Bodies

    Learning Objectives By the end of this section, you will be able to: Until now, we have considered the Sun and a planet (or a planet and one of its moons) as nothing more than a pair of bodies revolving around each other. In fact, all the planets exert gravitational forces upon one another as…

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