• This photograph of a rust-colored sunset was taken from Emerald Isle, part of the famous "Outer Banks" of North Carolina. Emerald Isle's island geography is at least partly responsible for the sunset's brilliant orange hue.

    The sun emits "white" light. White light is actually a combination of all the colors of the rainbow: red, orange, yellow, green, blue, indigo, and violet. Scientists and artists often use the acronym Roy G. Biv to remember these colors of the visible light spectrum. All colors have different wavelengths, from the very long (Roy) to the very short (Biv).

    The sun's white light is scattered by billions of tiny molecules as it filters through Earth's atmosphere. Light with short wavelengths (Biv) scatters much more easily than light with long wavelengths. Because of this, the sky usually appears blue as the sun shines down through the atmosphere during the day.

    As the sun rises and sets, however, its light passes through much more of Earth's atmosphere before reaching our eyes. Blue and violet light are scattered away. Only the long, reddish wavelengths can go the distance.

    What does all of this scattering have to do with brightly colored island sunsets? It comes down to what does the scattering.

    Earth's atmosphere—air—is mostly nitrogen and oxygen. Those molecules are pretty evenly spread out and do most of the sunlight-scattering around the world. Islands, however, are very close to the ocean. The air above them is filled with many more water and salt molecules than air further inland. All these "extra" molecules scatter even more blue light, leaving even more red light to reach our eyes.

    1. This is a sunset, viewed from the Outer Banks of North Carolina. Using this information, which direction is the photographer facing?

      The sun always rises in the east and sets in the west, no matter what your position on Earth. A person viewing a sunset is always facing west.

    2. Why would an orange-colored sunset like this be less likely to occur in Boulder, Colorado?

      The orange color is partly a result of the unique, humid atmosphere above the ocean. Boulder is landlocked, thousands of kilometers from the coast. The air around Boulder does not have the "extra" molecules of salt and water to scatter sunlight and produce bright orange sunsets.

    3. Particles of water and salt, in addition to nitrogen and oxygen, scatter light in the atmosphere. What other molecules do you think scatter light in the atmosphere, leading to dramatic, orange sunsets?

      Answers will vary. Molecules of dust, sand, volcanic ash, and air pollution (such as smog) all scatter light to create orange or red sunsets.

  • Term Part of Speech Definition Encyclopedic Entry
    air Noun

    the layer of gases surrounding Earth.

    Encyclopedic Entry: air
    atmosphere Noun

    layers of gases surrounding a planet or other celestial body.

    Encyclopedic Entry: atmosphere
    emit Verb

    to give off or send out.

    filter Verb

    to remove particles from a substance by passing the substance through a screen or other material that catches larger particles and lets the rest of the substance pass through.

    geography Noun

    study of places and the relationships between people and their environments.

    Encyclopedic Entry: geography
    island Noun

    body of land surrounded by water.

    Encyclopedic Entry: island
    molecule Noun

    smallest physical unit of a substance, consisting of two or more atoms linked together.

    nitrogen Noun

    chemical element with the symbol N, whose gas form is 78% of the Earth's atmosphere.

    ocean Noun

    large body of salt water that covers most of the Earth.

    Encyclopedic Entry: ocean
    Outer Banks Noun

    barrier islands off the coast of the U.S. state of North Carolina.

    oxygen Noun

    chemical element with the symbol O, whose gas form is 21% of the Earth's atmosphere.

    rainbow Noun

    multicolored arc produced by sunlight striking raindrops.

    Encyclopedic Entry: rainbow
    Roy G. Biv Noun

    device used to remember the colors of the visible spectrum: red, orange, yellow, green, blue, indigo, violet.

    scatter Verb

    to disperse or distribute without a clear pattern.

    sunset Noun

    time when the sun descends behind the horizon.

    visible light spectrum Noun

    light and colors that can be seen by human beings.

    wavelength Noun

    the distance between the crests of two waves.

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