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10.12: Solar Energy on Earth

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    Just how important is this star?

    Almost all energy at Earth's surface comes from the Sun. The Sun’s energy warms the planet and the air around it. This causes the atmosphere to move and create weather. Sunlight also powers photosynthesis and life on Earth.

    The Sun's Energy

    Most of the energy at Earth's surface comes from the Sun. Solar energy travels in tiny packets that move in waves. The waves have different wavelengths. Waves with different wavelengths carry different amounts of energy.

    Photons of Energy

    The Sun gives off energy in tiny packets called photons. Photons travel in waves. These waves make up electromagnetic radiation. The image below models a wave of light (Figure below). Notice the wavelength in the figure. Waves with shorter wavelengths have more energy.

    Diagram of a wave

    This curve models a wave. Based on this figure, how would you define wavelength?

    Electromagnetic Spectrum

    Energy from the Sun has a wide range of wavelengths. The total range of energy is called the electromagnetic spectrum (Figure below).

    The electromagnetic spectrum

    Compare the wavelengths of radio waves and gamma rays. Which type of wave has more energy?

    Visible light is the only light that humans can see. Different wavelengths of visible light appear as different colors. Radio waves have the longest wavelengths. They also have the least amount of energy. Infrared light has wavelengths too long for humans to see, but we can feel them as heat. The atmosphere absorbs the infrared light. Ultraviolet (UV) light is in wavelengths too short for humans to see. The most energetic UV light is harmful to life. The atmosphere absorbs most of this UV light from the Sun. Gamma rays have the highest energy, and they are the most damaging rays. Fortunately, gamma rays don’t penetrate Earth’s atmosphere.


    • Gamma rays have the most energy of any photons emitted by the sun while radio waves have the least. This range and the radiations within it make up the electromagnetic spectrum.
    • Solar energy travels in photons. Photons travel in waves, which make up electromagnetic radiation.
    • Visible light is the wavelengths of light humans can see.


    1. What is a photon? How does energy travel as photons?
    2. What is visible light? What has longer wavelengths than visible light? Shorter wavelengths?
    3. What is the electromagnetic spectrum?

    Explore More

    Use the resource below to answer the questions that follow.

    1. What is the electromagnetic spectrum?
    2. Which waves have the longest wavelengths?
    3. What has the shortest wavelengths?
    4. Why is the visible spectrum important?
    5. Stars are far away yet astronomers can tell when they are made of hydrogen. How?

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