Earth & Space Science

Earth & Space Science

  • About This Project
    • Preface/About
    • Author/Contributors
    • For Investors/Donors
    • Teaching Guide
  • Ch 1 – Our Place in the Universe
    • Chapter Introduction
    • 1.1 Our Cosmic Address
    • 1.1.1 Overview
    • 1.1.2 What do we mean when we say “Earth is a planet”?
    • 1.1.3 What is our solar system?
    • 1.1.4 What is a galaxy?
    • 1.1.5 What is the universe?
    • 1.1 Review: Our Cosmic Address
    • 1.2 The Scale of Space
    • 1.2.1 Overview
    • 1.2.2 How Big is the Earth–Moon System?
    • 1.2.3 How Big is our Solar System?
    • 1.2.4 How far are the stars?
    • 1.2.5 How big is the Milky Way Galaxy?
    • 1.2.6 How big is the universe?
    • 1.2 Review: The Scale of the Universe
    • 1.3 Spaceship Earth
    • 1.3.1 How is Earth moving in our solar system?
    • 1.3.2 How is our solar system moving in the Milky Way Galaxy?
    • 1.3.3 How does our galaxy move relative to other galaxies in the universe?
    • 1.3 Review
  • Ch 2 – Understanding the Sky
    • Chapter Introduction
    • 2.1 Our Everyday View of the Universe
    • 2.1.1 What do we see in the local sky?
    • 2.1.2 What is the celestial sphere?
    • 2.1.3 Why do stars rise and set?
    • 2.1.4 Why do we see different constellations at different times of year?
    • 2.1 Review
    • 2.2 Seasons
    • 2.2.1 What causes the seasons?
    • 2.2.2 How do seasons differ around the world?
    • 2.2.3 Does the orientation of Earth’s axis ever change?
    • 2.2 Review
    • 2.3 Viewing the Moon: Phases and Eclipses
    • 2.3.1 Why do we see phases of the Moon?
    • 2.3.2 When do we see different phases of the Moon in our sky?
    • 2.3.3 Why do we always see the same face of the Moon?
    • 2.3.4 What are eclipses?
    • 2.3 Review
    • 2.4 Planets in the Night Sky
    • 2.4.1 How do we recognize planets in the sky?
    • 2.4.2 Why do the planets “wander”?
    • 2.4 Review
  • Ch 3 – How Science Discovered the Earth
    • Chapter Introduction
    • 3.1 The Ancient View of Earth
    • 3.1.1 How did the ancient Greeks learn that Earth is round?
    • 3.1.2 Why didn’t the ancient Greeks realize that Earth orbits the Sun?
    • 3.1 Review
    • 3.2 The Copernican Revolution
    • 3.2.1 How did the idea of Earth as a planet gain favor?
    • 3.2.2 How did Galileo seal the case for Earth as a planet?
    • 3.2 Review
    • 3.3 The Nature of Modern Science
    • 3.3.1 How does science work?
    • 3.3.2 What is a “theory” in science?
    • 3.3.3 What is the value of science?
    • 3.3 Review
    • 3.4 The Fact and Theory of Gravity
    • 3.4.1 What is gravity?
    • 3.4.2 How does gravity hold us to the ground and make objects fall?
    • 3.4.3 Why does gravity make planets round?
    • 3.4.4 How does gravity govern motion in the universe?
    • 3.4 Review
  • Chapter 4 – Planet Earth
    • Chapter Introduction
    • 4.1 A Planetary Overview
    • 4.1.1 What does Earth look like on the outside?
    • 4.1.2 What does Earth look like on the inside?
    • 4.1.3 How has Earth changed through time?
    • 4.1.4 How do we study the Earth?
    • 4.1 Review
    • 4.2 Earth System Science
    • 4.2.1 What are Earth’s four major systems?
    • 4.2.2 What drives Earth system changes?
    • 4.2.3 What IS energy and how do we measure it?
    • 4.2 Review
    • 4.3 Earth In the Context of Other Worlds
    • 4.3.1 How does Earth compare to other worlds of our solar system?
    • 4.3.2 Could there be life on other worlds?
  • Chapter 5 – Earth Through Time
    • Chapter Introduction
    • 5.1 Learning from Rocks and Fossils
    • 5.1.1 How do rocks form?
    • 5.1.2 What are fossils?
    • 5.1.3 How do we learn the ages of rocks and fossils?
    • 5.1 Review
    • 5.2 Shaping Earth’s Surface
    • 5.2.1 How do continents differ from oceans?
    • 5.2.2 What processes shape continents?
    • 5.2.3 What dangers do geological changes pose?
    • 5.2 Review
    • 5.3 Plate Tectonics — The Unifying Theory of Earth’s Geology
    • 5.3.1 What evidence led to the idea that continents move?
    • 5.3.2 How does the theory of plate tectonics explain Earth’s major features?
    • 5.3 Review
    • 5.4 A Brief Geological History of Earth
    • 5.4.1 What major changes mark Earth’s fossil record?
    • 5.4.2 What killed the dinosaurs?
    • 5.4.3 Have we humans started a new geological epoch?
    • 5.4 Review
  • Chapter 6 – Air and Water
    • Chapter Introduction
    • 6.1 Atmosphere and Hydrosphere
    • 6.1.1 What exactly is the atmosphere?
    • 6.1.2 How is water distributed on Earth?
    • 6.1.3 How does water cycle through the hydrosphere and atmosphere?
    • 6.1 Review
    • 6.2 Global Winds and Currents
    • 6.2.1 What drives global winds and currents?
    • 6.2.2 What is the general pattern of winds on Earth?
    • 6.2.3 What is the general pattern of ocean currents?
    • 6.2 Review
    • 6.3 Weather and Climate
    • 6.3.1 What is the difference between weather and climate?
    • 6.3.2 How and why does climate vary around the world?
    • 6.3.3 How do we measure and predict the weather?
  • Chapter 7 – Human Impact on the Climate
    • Chapter Introduction
    • 7.1 The Basic Science of Global Warming
    • 7.1.1 What is the greenhouse effect?
    • 7.1.2 How is human activity strengthening Earth’s greenhouse effect?
    • 7.1.3 How do we know that global warming is really happening and is human-caused?
    • 7.1.4 How does human-caused climate change compare to natural climate change?
    • 7.1 Review
    • 7.2 Consequences of Global Warming
    • 7.2.1 What are the major consequences of global warming?
    • 7.2.2 How do scientists predict future consequences of global warming?
    • 7.2.3 How will climate changes affect you and others around the world?
    • 7.2 Review
    • 7.3 Solutions to Global Warming
    • 7.3.1 What existing technologies could solve the problem of global warming?
    • 7.3.2 What future technologies might help even more?
    • 7.3.3 What does it take to implement a solution?
    • 7.3.4 What will your world look like AFTER we solve global warming?
    • 7.3 Review

I was wondering...

Is there a name for the shortest path on a sphere?

The shortest path between two points on a flat surface or in space follows a straight line, and we therefore say that the path itself is a “line segment” (because segment means “a piece of”). But on a sphere like the Earth, the shortest path is curved, not straight, because it is a portion of a great circle. So what do we call it? The answer is that it is called a geodesic. In fact, the term geodesic can be used to describe the shortest path between two points on any surface, whether it is a sphere, a plane, or something else. For example, if you draw the shortest path between two points on a lamp shade, it will be curved in a different way from the shortest path on a sphere, but the path is still called a geodesic.

These illustrations show geodesics — meaning the shortest path between two points — for both a sphere and a lamp shade.

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